Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools


[Document Version: 2.07] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools

Author: Samuel M. Goldwasser
Corrections/suggestions: | Email

Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

Chapter 2) Introduction

  2.1) Where do you keep your dead appliances?

If you have ever tried to get a small household appliance or portable power
tool repaired, you understand why all that stuff is likely to be gathering
dust in your attic or basement closet or junk box.  It does not pay!  This
may be partially by design.  However, to be fair, it may take just as much
time to diagnose and repair a problem with a $20 toaster as a $300 VCR and
time is money for a repair shop.  It is often not even economical to repair
the more expensive equipment let alone a $40 electric heater.  The cost
of the estimate alone would probably buy at least one new unit and possibly
many more.

However, if you can do the repair yourself, the equation changes dramatically
as your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.  The educational aspects may also be
appealing.  You will learn a lot in the process.  Many problems can be
solved quickly and inexpensively.  Fixing an old vacuum cleaner to keep
in the rec room may just make sense after all.

This document provides maintenance and repair information for a large number
of small household appliances and portable power tools.  The repair of
consumer electronic equipment is dealt with by other documents in the
"Notes on the Troubleshooting and Repair of..." series.  Suggestions for
additions (and, of course, correction) are always welcome.

You will be able to diagnose problems and in most cases, correct them as
well.  Most problems with household appliances are either mechanical (e.g.,
dirt, lack of or gummed up lubrication, deteriorated rubber parts, broken
doohickies) or obvious electrical (e.g., broken or corroded connections,
short circuits, faulty heating elements) in nature.  With minor exceptions,
specific manufacturers and models will not be covered as there are so many
variations that such a treatment would require a huge and very detailed text.
Rather, the most common problems will be addressed and enough basic principles
of operation will be provided to enable you to narrow the problem down and
likely determine a course of action for repair.  In many cases, you will
be able to do what is required for a fraction of the cost that would be
charged by a repair center - or - be able to revive something that would
otherwise have gone into the dumpster - or remained in that closet until
you moved out of your house (or longer)!

Since so many appliances are variations on a theme - heating, blowing,
sucking, rotating, etc. - it is likely that even if your exact device does
not have a section here, a very similar one does.  Furthermore, with your
understanding of the basic principles of operation, you should be able to
identify what is common and utilize info in other sections to complete a

Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair (recommended), alt.home.repair,
or misc.consumers.house.  It will also be easier to do further research using
a repair textbook.  In any case, you will have the satisfaction of knowing you
did as much as you could before finally giving up or (if it is worthwhile
cost-wise) taking it in for professional repair.  With your newly gathered
knowledge, you will have the upper hand and will not easily be snowed by a
dishonest or incompetent technician.

Chapter 3) Some Tidbits

You may not realize the following:

* Virtually any table lamp can be restored to a like-new condition
  electrically for less than $5 in parts.

* The cause of a vacuum cleaner that starts blowing instead of sucking
  is likely a dirt clog somewhere.  It is virtually impossible for the
  motor to spin in the wrong direction and even if it did, the vacuum
  would still have some suction due to the type of blower that is commonly

* Many diagnoses of burned out motors are incorrect.  Very often motor
  problems are actually something else - and minor.  A truly burned out
  motor will often have died spectacularly and under adverse conditions.
  It will likely be smelly, charred, or may have created lots of sparks,
  tripped a circuit breaker or blew a fuse.  A motor that just stopped
  working may be due to worn (carbon) brushes, dirt, or a fault elsewhere
  in the appliance like a bad connection or switch or circuit - or the AC
  outlet might be bad.

* Fluorescent lamps use only 1/3 to 1/2 of the power of an incandescent lamp
  of similar light output.  With all the lighting used in an average household,
  this can add up particularly for high power ceiling fixtures.  However,
  fluorescent light color and quality may not be as aesthetically pleasing
  and fixtures or lamps may produce Radio Frequency Interference (RFI) causing
  problems with TV or radio reception.  Dimmers can usually not be used
  unless they are specifically designed for fluorescent fixtures.  Compact
  fluorescent lamps do indeed save energy but they can break just like any
  other light bulb!

* The initial inrush current to an incandescent bulb may be 10 times the
  operating current.  This is hard on switches and dimmers and is part of
  the reason behind why bulbs tend to burn out when switched on and not
  while just sitting there providing illumination.  Furthermore, an erratic
  switch or loose connection can shorten the life of an incandescent bulb
  due to repeated thermal shock.  And, these are not due to short circuits
  but bad intermittent connections.  True short circuits are less common
  and should result in a blown fuse or tripped circuit breaker.

* Bulb Savers and other devices claiming to extend the life of incandescent
  light bulbs may work but do so mostly by reducing power to the bulb at the
  expense of some decrease in light output and reduced efficiency.  It is
  estimated that soft start alone (without the usual associated reduction in
  power) does not prolong the life of a typical bulb by more than a few hours.

  Thus, in the end, these device increase costs if you need to use more or
  larger bulbs to make up for the reduced light output.  The major life cycle
  expense for incandescent lighting is not the cost of the bulbs but the cost
  of the electricity - by a factor of 25 to 50!  For example, it costs about
  $10 in electricity to run a 100 W bulb costing 25 cents over the course of
  its 1000 hour life.  However, these devices (or the use of 130 V bulbs) may
  make sense for use in hard-to-reach locations.  Better yet, consider compact
  or normal fluorescent bulbs or fixtures which last much longer and are much
  more efficient than incandescents (including halogen).

* Smart bulbs are legitimate technology with built in automatic off, dimmers,
  blink capability, and other 'wizzy' features but they burn out and break just
  like ordinary bulbs.  Thus, it hardly makes sense to spend $5 to $10 for
  something that will last 1000 to 1500 hours.  Install a proper dimmer,
  automatic switch, or external blinker instead.

* A Ground Fault Circuit Interrupter (GFCI) protects people against shock
  but does not necessarily protect appliances from damage due to electrical
  faults.  This is the function of fuses, circuit breakers, and thermal
  protectors. A GFCI *can* generally be installed in place of a 2-wire
  ungrounded outlet to protect it and any outlets downstream.  Check your
  local electrical Code to be sure if this is permitted.

* Don't waste your money on products like the 'Green Plug', magnetic water
  softeners, whole house TV antennas that plug into the wall socket, and
  other items of the "it sounds too good to be true' variety.  These are very
  effective only at transferring money out of your wallet but rarely work as

  - The Green Plug will not achieve anywhere near the claimed savings and may
    actually damage or destroy certain types of appliances like, guess what?:
    refrigerators and other induction motor loads.  Ever seen the demo?

    The Green Plug is supposed to reduce reactive power (V and I out of phase
    due to inductive or capacitive loads) but residential users don't pay for
    reactive power anyway, only the real power they use.  In addition, this is
    a minor concern for modern appliances.

    The demo you see in the store that shows a utility meter slowing down
    substantially when the Green Plug is put in the circuit is bogus for two
    reasons: (1) The motor being powered is totally unloaded resulting in a
    high ratio of reactive to real power.  Under normal use with a motor
    driving a load, the reduction in electricity use would be negligible.
    (2) The meter is wired to include reactive power in its measurement which,
    as noted above, is not the case with residential customers.

  - Magnetic and radio frequency water softeners are scams - pure and simple.
    They cloak absolutely useless technology in so much 'technobabble' that
    even Ph.D. scientists and engineers have trouble sorting it all out.
    The latest wrinkle adds advanced microprocessor control optimized for
    each potential mineral deposit.  Yeh, sure.

    Mention the word 'magnetism' and somehow, people will pay $300 for $2
    worth of magnets that do nothing - and then be utterly convinced of their
    effectiveness.  They forget that perhaps the instruction manual suggested
    changes in their water use habits - which was the true reason for any
    improvement.  Perhaps the magnets can be used to stick papers on the
    refrigerator once you discover they don't do anything for the water.

    BTW, the same goes for magnetic wine flavor enhancers :-).

  - Whole house TV antennas are great for picking up signals with ghosts,
    noise, and other distorting effects.  The premise that 'more is better'
    is fundamentally flawed when it comes to TV reception.  In rare cases
    they may produce a marginally viewable picture in an otherwise unfavorable
    location but these are the exceptions.  A pair of set-top rabbit ears will
    generally be superior.

  I will be happy to revise these comments if someone can provide the results
  of evaluations of any of these devices conducted by a recognized independent
  testing laboratory.  However, I won't hold my breath waiting.

Chapter 4) Basic Appliance Theory

  4.1) What is inside an appliance?

There isn't much rocket science in the typical small appliance (though that
is changing to some extent with the use of microcomputer and fuzzy logic
control).  Everything represents variations on a relatively small number
of basic themes:

* Heating - a resistance element similar to what you can see inside a
  toaster provides heat to air, liquids, or solids by convections,
  conduction, or direct radiant (IR) heat.

* Rotation, blowing, sucking - a motor provides power to move air as in
  a fan or vacuum cleaner, water as in a sump pump, or provide drive as
  in an electric pencil sharpener, food mixer, or floor polisher.

* Control - switches and selectors, thermostats and speed regulators,
  and microcomputers determine what happens, when, how much, and assure
  safe operation.

  4.2) Basic electrical principles

Relax! This is not going to be a tutorial on computer design.  Appliances
are simple devices.  It is possible to repair many appliance faults without
any knowledge beyond 'a broken wire is probably a problem' or 'this part
is probably bad because it is charred and broken in half'.  However, a
very basic understanding of electrical principles will enable you to more
fully understand what you are doing.  Don't worry, there will be no heavy
math.  The most complicated equations will be variations on Ohm's law:
V=I*R and P=V*V/R.

  4.3) Voltage, current, and resistance

If you have any sort of background in electricity or electronics, then
you can probably skip the following introductory description - or have
some laughs at my expense.

The easiest way to explain basic electrical theory without serious math
is with a hydraulic analogy.  This is of the plumbing system in your house:

Water is supplied by a pipe in the street from the municipal water company
or by a ground water pump.  The water has a certain pressure trying to
push it through your pipes.  With electric circuits, voltage is the analog
to pressure.  Current is analogous to flow rate.  Resistance is analogous
the difficulty in overcoming narrow or obstructed pipes or partially open

Intuitively, then, the higher the voltage (pressure), the higher the
current (flow rate).   Increase the resistance (partially close a valve or
use a narrower pipe) and for a fixed voltage (constant pressure), the
current (flow rate) will decrease.

With electricity, this relationship is what is known as linear: double the
voltage and all other factors remaining unchanged, the current will double
as well.  Increase it by a factor of 3 and the current will triple.  Halve
the resistance and for a constant voltage source, the current will double.
(For you who are hydraulic engineers, this is not quite true with plumbing
as turbulent flow sets in, but this is just an analogy, so bear with me.)

Note: for the following 4 items whether the source is Direct Current (DC)
such as a battery or Alternating Current (AC) from a wall outlet does not
matter.  The differences between DC and AC will be explained later.

The simplest electrical circuit will consist of several electrical
components in series - the current must flow through all of them to flow
through any of them.  Think of a string of Christmas lights - if one burns
out, they all go out because the electricity cannot pass through the broken
filament in the burned out bulb.

Note the term 'circuit'.  A circuit is a complete loop.  In order for
electricity to flow, a complete circuit is needed.

                          Switch (3)
               _____________/ ______________
              |                             |
              | (1)                         | (4)
      +-------+--------+                +---+----+
      |  Power Source  |                |  Load  |
      +-------+--------+                +---+----+
              |            Wiring (2)       |
1. Power source - a battery, generator, or wall outlet.  The hydraulic
   equivalent is a pump or dam (which is like a storage battery).  The
   water supply pipe in the street is actually only 'wiring' (analogous
   to the electric company's distribution system) from the water company's
   reservoir and pumps.

2. Conductors - the wiring.  Similar to pipes and aqueducts.  Electricity
   flows easily in good conductors like copper and aluminum.  These are like
   the insides of pipes.  To prevent electricity from escaping, an insulator
   like plastic or rubber is used to cover the wires.  Air is a pretty
   good insulator and is used with high power wiring such as the power
   company's high voltage lines but plastic and rubber are much more
   convenient as they allow wires to be bundled closely together.

3. Switch - turns current on or off.  These are similar to valves which
   do not have intermediate positions, just on and off.  A switch is not
   actually required in a basic circuit but will almost always be present.

4. Load - a light bulb, resistance heater, motor, solenoid, etc.  In
   true hydraulic systems such as used to control the flight surfaces of
   an aircraft, there are hydraulic motors and actuators, for example.

   With household water we usually don't think of the load.

Here are 3 of the simplest appliances:

* Flashlight: battery (1), case and wiring (2), switch (3), light bulb (4).

* Table lamp: wall outlet (1), line cord and internal wiring (2), power
  switch (3), light bulb (4).

* Electric fan, vacuum cleaner, garbage disposer: wall outlet (1), line
  cord and internal wiring (2), power switch (3), motor (4).

Now we can add some simple control devices:

5. Thermostat - a switch that is sensitive to temperature.  This is like an
   automatic water valve which shuts off if a set temperature is exceeded.
   Most thermostats are designed to open the circuit when a fixed or variable
   temperature is exceeded.  However, airconditioners, refrigerators, and
   freezers do the opposite - the thermostat switches on when the temperature
   goes too high.  Some are there only to protect against a failure elsewhere
   due to a bad part or improper use that would allow the temperature to
   go too high and start a fire.  Others are adjustable by the user and
   provide the ability to control the temperature of the appliance.

With the addition of a thermostat, many more appliances can be constructed
including (this is a small subset):

* Electric space heater (radiant), broiler, waffle iron: wall outlet (1),
  line cord and internal wiring (2), power switch (3) and/or thermostat (5),
  load (heavy duty heating element).

* Electric heater (convection), hair dryer: wall outlet (1), line cord
  and internal wiring (2), power switch (3) and/or thermostat (5), loads (4)
  (heating element and motor).

Electric heaters and cooking appliances usually have adjustable thermostats.

Hair dryers may simply have several settings which adjust heater power and
fan speed (we will get into how later).  The thermostat may be fixed and
to protect against excessive temperatures only.

That's it!  You now understand the basic operating principle of nearly all
small appliances.  Most are simply variations (though some may be quite
complex) on these basic themes.  Everything else is just details.

For example, a blender with 38 speeds just has a set of buttons (switches)
to select various combinations of motor windings and other parts to give
you complete control (as if you need 38 speeds!).  Toasters have a timer
or thermostat activate a solenoid (electromagnet) to pop your bread at
(hopefully) the right time.

5. Resistances - both unavoidable and functional.  Except for superconductors,
   all materials have resistance.  Metals like copper, aluminum, silver, and
   gold have low resistance - they are good conductors.  Many other metals
   like iron or steel are fair but not quite as good as these four.  One,
   NiChrome - an alloy of nickel and chromium - is used for heating elements
   because it does not deteriorate (oxidize) in air even at relatively high

   A significant amount of the power the electric company produces is lost
   to heating of the transmission lines due to resistance and heating.

   However, in an electric heater, this is put to good use.  In a flashlight
   or table lamp, the resistance inside the light bulb gets so hot that it
   provides a useful amount of light.

   A bad connection or overloaded extension cord, on the other hand, may
   become excessively hot and start a fire.

The following is more advanced - save for later if you like.

6. Capacitors - energy storage devices.  These are like water storage tanks
   (and similar is some ways to rechargeable batteries).

   Capacitors are not that common in small appliances but may be used with
   some types of motors and in RFI - Radio Frequency Interference - filters
   as capacitors can buffer - bypass - interference to ground.  The energy
   to power an electronic flash unit is stored in a capacitor, for example.
   Because they act like reservoirs - buffers - capacitors are found in the
   power supplies of most electronic equipment to smooth out the various
   DC voltages required for each device.

7. Inductors - their actual behavior is like the mass of water as it flows.
   Turn off a water faucet suddenly and you are likely to hear the pipes
   banging or vibrating.  This is due to the inertia of the water - it tends
   to want to keep moving.  Electricity doesn't have inertia but when wires
   are wound into tight coils, the magnetic field generated by electric
   current is concentrated and tends to result in a similar effect.  Current
   tends to want to continue to flow where inductance is present.

   The windings of motors and transformers have significant inductance but
   the use of additional inductance devices is rare in home appliances
   except for RFI - since inductance tends to prevent current from changing,
   it can also be used to prevent interference from getting in or out.

8. Controls - rheostats and potentiometers allow variable control of current
   or voltage.  A water faucet is like a variable resistor which can be
   varied from near 0 ohms (when on fully) to infinite ohms (when off).

  4.4) Ohm's Law

The relationships that govern the flow of current in basic circuits (without
capacitance or inductance - which is the case with many appliances) are
contained in a very simple set of equations known an Ohm's Law.

The simplest of these are:

                    V = I * R (1)
                    I = V / R (2) 
                    R = V / I (3)


     V is Voltage in Volts (or millivolts - mV or kilovolts - KV).
     I is current in amperes (A) or milliamps (mA) 
     R is resistance in Ohms (ohms), kilo-Ohms (K Ohms), or mega-Ohms (M Ohms).

Power in watts (W) is equal to voltage times current in a resistive circuit
(no capacitance or inductance).  Therefore, rearranging the equations above,
we also obtain:

                    P = V * I      (4)
                    P = V * V / R  (5)
                    P = I * I * R  (6)

For example:

* For a flashlight with a pair of Alkaline batteries (3 V) and a light bulb
  with a resistance of 10 ohms, we can use (2) to find that the current
  is I = (3 V) / (10 ohms) = .3 A.  The from (4) we find that the power
  is: P = (3 V * .3 A) = .9 W.

* For a blow-dryer rated at 1000 W, the current drawn from a 120 V line
  would be: I = P / V (by rearranging (4) = 1000 W / 120 V = 8.33 A.

As noted above:

* Increase voltage -> higher current.  (If the water company increases the
  pressure, your shower used more water in a given time.)

* Decrease resistance -> higher current.  (You have a new wider pipe installed
  between the street and your house.  Or, you open the shower valve wider.)

(Note that the common use of the term 'water pressure' is actually not
correct.  The most likely cause of what is normally described as low
water pressure is actually high resistance in the piping between your
residence and the street.  There is a pressure drop in this piping just
as there would be a voltage drop across a high value resistor.)

  4.5) DC and AC

While electricity can vary in any way imaginable, the most common forms
for providing power are direct current and alternating current:

A direct current source is at a constant voltage.  Displaying the voltage
versus time plot for such a source would show a flat line at a constant
level.  Some examples:

  * Alkaline AA battery - 1.5 V (when new).
  * Automotive battery - 12 V (fully charged).
  * Camcorder battery - 7.2 V (charged).
  * Discman AC adapter - 9 VDC (fully loaded).
  * Electric knife AC adapter - 3.6 VDC.

An Alternating Current (AC) source provides a voltage that is varying
periodically usually at 60 Hz (U.S.) or 50 Hz (many other countries).
Note that 1 Hz = 1 cycle per second.  Therefore, a 60 Hz AC voltage
goes through 60 complete cycles in each second.  For power, the shape
of the voltage is a sinusoid which is the smoothest way that anything
can vary periodically between two levels.

The nominal voltage from an AC outlet in the U.S. is around 115 VAC.  This
is the RMS (Root Mean Square) value, not the peak (0 to maximum).  In simple
terms, the RMS value of an AC voltage and the same value of a DC voltage
will result in identical heating (power) to a resistive load.  For example,
115 VAC RMS will result in the same heat output of a broiler as 115 VDC.

Direct current is used for many small motor driven appliances particularly
when battery power is an option since changing DC into AC requires some
additional circuitry.  All electronic equipment require various DC voltages
for their operation.  Even when plugged into an AC outlet, the first thing
that is done internally (or in the AC adapter in many cases) is to convert
the AC to various DC voltages.

The beauty of AC is that a very simple device - a transformer - can
convert one voltage into another.  This is essential to long distance
power distribution where a high voltage and low current is desirable to
minimize power loss (since it depends on the current).  You can see
transformers atop the power poles in your neighborhood reducing the
2,000 VAC or so from a local distribution transformer to your 115 VAC
(actually, 115-0-115 were the total will be used by large appliances like
electric ranges and clothes dryers).  That 2,000 VAC was stepped down
by a larger transformer from around 12,000 VAC provided by the local
substation.  This, in turn, was stepped down from the 230,000 VAC or
more used for long distance electricity transmission.  Some long distance
lines are over 1,000,000 volts (MV).

When converting between one voltage and another with a transformer, the
amount of current (amps) changes in the inverse ratio.  So, using 230 KV
for long distance power transmission results in far fewer heating losses
as the current flow is reduced by a factor of 2,000 over what it would
be if the voltage was only 115 V, for example.  Recall that power loss
from P=I*I*R is proportional to the square of the current and thus in
this example is reduced by a factor of 4,000,000!

Many small appliances include power transformers to reduce the 115 VAC
to various lower voltages used by motors or or electrical components.
Common AC adapters - often simply called transformers or wall warts -
include a small transformer as well.  Where their output is AC, this
is the only internal component other than a fuse or thermal fuse for
protection.  Where their output is DC, additional components convert
the low voltage AC from the transformer to DC and a capacitor smoothes
it out.

  4.6) Series and parallel circuits

Up until now, we have been dealing with the series circuit - all parts
are in a single line from power source, wiring, switches, load, and
anything else.  In a series circuit, the current must be the same
through all components.  The light bulb and switch in a flashlight
pass exactly the same value of amperes.  If there were two light bulbs
instead of one and they were connected in series - as in a Christmas
tree light set - then the current must be equal in all the bulbs but
the voltages across each one would be reduced.

The loads, say resistance heating elements, are now drawn with the
schematic symbol (as best as can be done using ASCII) for a resistor.

               _____________/ __________________
              |                 I -->           |
              |                        ^    ^   |
              |                        |    |   / R1
              |                        |   V1   \ Load 1
      +-------+--------+               |    |   /
      |  Power Source  |                    v__ |
      +-------+--------+              V(S)  ^   |
              |                             |   / R2
              |                        |   V2   \ Load 2
              |                        |    |   /
              |                        v    v   |

The total resistance, R(T), of the resistors in this series circuit is:

                    R(T) = R1 + R2                (7)

The voltage across each of the resistors would be given by:

                    V1 = V(S) * R1 / (R1 + R2)    (8)
                    V2 = V(S) * R2 / (R1 + R2)    (9)

The current is given by:

                    I = V(S)  / (R1 + R2)        (10)

However, another basic configuration, is also possible.  With a parallel
circuit, components are connected not one after the other but next to
one another as shown below:

               _____________/ ___________________________
              |                      I -->  |            |
              |                 ^           |            |
      +-------+--------+        |           / R1         / R2
      |  Power Source  |       V(S)         \ Load 1     \ Load 2
      +-------+--------+        |           /            /
              |                 v           |v I(1)      |v I(2)

Now, the voltages across each of the loads is necessarily equal but the
individual currents divide according to the relative resistances of each

The total resistance, R(T), of the parallel resistors in this circuit is:

                    R(T) = (R1 * R2) / (R1 + R2)  (11)

The currents through each of the loads would be given by:

                    I1 = V(S)/R1                  (12)
                    I2 = V(S)/R2                  (13)

The total current is given by:

                    I = I1 + I2                   (14)

Many variations on these basic arrangements are possible but nearly all can
be reduced systematically to a combination of series or parallel circuits.

Chapter 5) Appliance Troubleshooting

  5.1) SAFETY

Appliances run on either AC line power or batteries.  In the latter case,
there is little danger to you except possibly from burns due to short circuits
and heating effect or irritation from the caustic chemicals from old leaky

However, AC line power can be lethal.  Proper safety procedures must be
followed whenever working on live equipment (as well as devices which may
have high energy storage capacitors like TVs, monitors, and microwave
ovens).  AC line power due to its potentially very high current is actually
considerably more dangerous than the 30 KV found in a large screen
color TV!

These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.

Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart.  Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage - there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.

  5.2) Safety myths

For nearly all the appliances we will be covering, there is absolutely
no danger of electrical shock once the unit is unplugged from the wall
socket (not, however, just turned off, but unplugged).

You may have heard warnings about dangers from unplugged appliances.
Perhaps, these were passed down from your great great grandparents or
from local bar room conversation.

Except for devices with large high voltage capacitors connected to the
line or elsewhere, there is nothing inside an appliance to store a
painful or dangerous charge.  Even these situations are only present
in microwave ovens, fluorescent lamps and fixtures with electronic
ballasts, universal power packs for camcorders or portable computers,
or appliances with large motors.  Other than these, once an appliance
is unplugged all parts are safe to touch - electrically that is.  There
may still be elements or metal brackets that are burning hot as metal
will tend to retain heat for quite a while in appliances like toasters
or waffle irons.  Just give them time to cool.  There are often many
sharp edges on sheetmetal as well.  Take your time and look before you
leap or grab anything.

  5.3) Safety guidelines

The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions.  Appliance repair can be
both rewarding and economical.  Just be sure that it is also safe!

* Don't work alone - in the event of an emergency another person's presence
  may be essential.

* Always keep one hand in your pocket when anywhere around a powered
  line-connected or high voltage system.

* Wear rubber bottom shoes or sneakers.

* Wear eye protection - large plastic lensed eyeglasses or safety goggles.

* Don't wear any jewelry or other articles that could accidentally contact
  circuitry and conduct current, or get caught in moving parts.

* Set up your work area away from possible grounds that you may accidentally

* Know your equipment: small appliances with 2 prong plugs do not use any
  part of the outside case for carrying current.  Any metal parts of the
  case will either be totally isolated or possibly connected to one side
  of the line through a very high value resistor and/or very low value
  capacitor.  However, there may be exceptions.  And, failures may occur.
  Appliances with 3 prong plugs will have the case and any exposed metal
  parts connected to the safety ground.

* If circuit boards or other subassemblies need to be removed from their
  mountings, put insulating material between them and anything they may
  short to.  Hold them in place with string or electrical tape.  Prop them
  up with insulation sticks - plastic or wood.

* Parts of heating appliances can get very hot very quickly.  Always carefully
  test before grabbing hold of something you will be sorry about later.

* If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 2 W or greater
  resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor
  use a 50 K ohm resistor).  The only places you are likely to find large
  capacitors in small appliance repair are in induction motor starting or
  running circuitry or the electronic ballasts of fluorescent fixtures.

* Connect/disconnect any test leads with the equipment unpowered and
  unplugged. Use clip leads or solder temporary wires to reach cramped
  locations or difficult to access locations.

* Perform as many tests as possible with the device unplugged.  Even with
  the power switch supposedly off, if the unit is plugged into a live outlet,
  line voltage may be present in unexpected places or probing may activate
  a motor due to accidentally pressing a microswitch.  Most parts in
  household appliances and power tools can be can be tested using only
  an ohmmeter or continuity checker.

* If you must probe live, put electrical tape over all but the last 1/16"
  of the test probes to avoid the possibility of an accidental short which
  could cause damage to various components.  Clip the reference end of the
  meter or scope to the appropriate ground return so that you need to only
  probe with one hand.

* Use an isolation transformer if there is any chance of contacting line
  connected circuits.  A Variac(tm) is not an isolation transformer!

  The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
  good idea but will not protect you from shock from many points in a line
  connected TV or monitor, or the high voltage side of a microwave oven, for
  example.  (Note however, that, a GFCI may nuisance trip at power-on or at
  other random times due to leakage paths (like your scope probe ground) or
  the highly capacitive or inductive input characteristics of line powered
  equipment.)  A fuse or circuit breaker is too slow and insensitive to provide
  any protection for you or in many cases, your equipment.  However, these
  devices may save your scope probe ground wire should you accidentally connect
  it to a live chassis.

* Don't attempt repair work when you are tired.  Not only will you be more
  careless, but your primary diagnostic tool - deductive reasoning - will
  not be operating at full capacity.

* Finally, never assume anything without checking it out for yourself!
  Don't take shortcuts!

  5.4) Should I unplug appliances when not in use?

There is no hard and fast rule.  Personally, I do unplug heating appliances
when I am done with them.  The quality of internal construction is not always
that great and this is a minor annoyance to avoid a possible fire hazard
should something fail or should such an appliance accidentally be left on.

BTW, electronic equipment should always be unplugged during lightning
storms since it may be very susceptible to power surge and lightning
damage.  Don't forget the telephones and computer modems as well.
This is not as much of a problem with small appliances that do not
include electronic controllers as except for direct lightning strikes,
the power switch will provide protection.

  5.5) Troubleshooting tips

Many problems have simple solutions.  Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures.  For a dead appliance, the most likely cause might just be
a bad line cord or plug!  Try to remember that the problems with the most
catastrophic impact on operation (an appliance that blows fuses) usually
have the simplest causes (a wire shorting due to frayed insulation).

If you get stuck, sleep on it.  Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution.  Don't work when you are really tired - it is both
dangerous and mostly non-productive (or possibly destructive - especially
with AC line powered appliances).

Whenever working on precision equipment, make copious notes and diagrams.
Yes, I know, a toaster may not exactly be precision equipment, but trust me.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always.  Apparently identical screws may be of differing
lengths or have slightly different thread types.  Little parts may fit in
more than one place or orientation.  Etc.  Etc.

Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly.

Select a work area which is well lighted and where dropped parts can
be located - not on a deep pile shag rug.  Something like a large plastic
tray with a slight lip may come in handy as it prevents small parts from
rolling off of the work table.  The best location will also be relatively
dust free and allow you to suspend your troubleshooting to eat or sleep or
think without having to pile everything into a cardboard box to eat dinner.

  5.6) Basic hand tools

A basic set of precision hand tools will be all you need to work on
most appliances.  These do not need to be really expensive but poor quality
tools are worse than useless and can cause damage.  Stanley and Craftsman
tools are fine.  Needed tools include a selection of Philips and straight
blade screwdrivers, socket drivers, open end or adjustable wrenches of various
sizes, needlenose pliers, wire cutters, tweezers, and dental picks.

An electric drill or drill press with a set of small (1/16" to 1/4") high
quality high speed drill bits is handy for some types of restoration where
new holes need to be provided.  A set of machine screw taps is also useful
at times.

A medium power soldering iron and rosin core solder (never never use
acid core solder or the stuff for sweating copper pipes on electrical
or electronic repairs!) will be required if you need to make or replace any
soldered connections.  A soldering gun is desirable for any really beefy
soldering.  See the section: "Soldering techniques".

A crimping tool and an assortment of solderless connectors often called
'lugs' will be needed to replace damaged or melted terminals in small
appliances.  See the section: "Solderless connectors".

Old dead appliances can often be valuable sources of hardware and sometimes
even components like switches and heating elements.  While not advocating
being a pack rat, this does have its advantages at times.

  5.7) Soldering techniques

Soldering is a skill that is handy to know for many types of construction
and repair.  For modern small appliances, it is less important than it once
was as solderless connectors have virtually replaced solder for internal

However, there are times where soldering is more convenient.  Use of the
proper technique is critical to reliability and safety.  A good solder
connection is not just a bunch of wires and terminals with solder dribbled
over them.  When done correctly, the solder actually bonds to the surface
of the metal (usually copper) parts.

Effective soldering is by no means difficult but some practice may be needed
to perfect your technique.

The following guidelines will assure reliable solder joints:

* Only use rosin core solder (e.g., 60/40 tin/lead) for electronics work.
  A 1 pound spool will last a long time and costs about $10.  Suggested
  diameter is .030 to .060 inches for appliances.  The smaller size is
  preferred as it will be useful for other types of precision electronics
  repairs or construction as well.  The rosin is used as a flux to clean
  the metal surface to assure a secure bond.  NEVER use acid core solder
  or the stuff used to sweat copper pipes!  The flux is corrosive and
  it is not possible to adequately clean up the connections afterward to
  remove all residue.

* Keep the tip of the soldering iron or gun clean and tinned.  Buy tips that
  are permanently tinned - they are coated and will outlast countless normal
  copper tips.  A quick wipe on a wet sponge when hot and a bit of solder
  and they will be as good as new for a long time.  (These should never be
  filed or sanded).

* Make sure every part to be soldered - terminal, wire, component leads -
  is free of any surface film, insulation,  or oxidation.  Fine sandpaper or
  an Xacto knife may be used, for example, to clean the surfaces.  The secret
  to a good solder joint is to make sure everything is perfectly clean
  and shiny and not depend on the flux alone to accomplish this. Just make
  sure the scrapings are cleared away so they don't cause short circuits.

* Start with a strong mechanical joint.  Don't depend on the solder to
  hold the connection together.  If possible, loop each wire or component
  lead through the hole in the terminal.  If there is no hole, wrap them
  once around the terminal.  Gently anchor them with a pair of needlenose

* Use a properly sized soldering iron or gun: 20-25 W iron for fine circuit
  board work; 25-50 W iron for general soldering of terminals and wires
  and power circuit boards; 100-200 W soldering gun for chassis and large
  area circuit planes.  With a properly sized iron or gun, the task will be
  fast - 1 to 2 seconds for a typical connection - and will result in little
  or no damage to the circuit board, plastic switch housings, insulation,
  etc.  Large soldering jobs will take longer but no more than 5 to 10
  seconds for a large expanse of copper.  If it is taking too long, your
  iron is undersized for the task, is dirty, or has not reached operating
  temperature.  For appliance work there is no need for a fancy soldering
  station - a less than $10 soldering iron or $25 soldering gun as
  appropriate will be all that is required.

* Heat the parts to be soldered, not the solder.  Touch the end of the solder
  to the parts, not the soldering iron or gun.  Once the terminal, wires,
  or component leads are hot, the solder will flow via capillary action, fill
  all voids, and make a secure mechanical and electrical bond.  Sometimes,
  applying a little from each side will more effectively reach all nooks
  and crannies.

* Don't overdo it.  Only enough solder is needed to fill all voids.  The
  resulting surface should be concave between the wires and terminal, not
  bulging with excess solder.

* Keep everything absolutely still for the few seconds it takes the solder
  to solidify.  Otherwise, you will end up with a bad connection - what is
  called a 'cold solder joint'.

* A good solder connection will be quite shiny - not dull gray or granular.
  If your result is less than perfect reheat it and add a bit of new solder
  with flux to help it reflow.

Practice on some scrap wire and electronic parts.  It should take you about
3 minutes to master the technique!

  5.8) Desoldering techniques

Occasionally, it will be necessary to remove solder - either excess or
to replace wires or components.  A variety of tools are available for
this purpose.  The one I recommend is a vacuum solder pump called
'SoldaPullet' (about $20).  Cock the pump, heat the joint to be cleared,
and press the trigger.  Molten solder is sucked up into the barrel of the
device leaving the terminal nearly free of solder.  Then use a pair of
needlenose pliers and a dental pick to gently free the wires or component.
Other approaches that may be used in place of or in addition to this:
Solder Wick which is a copper braid that absorbs solder via capillary
action; rubber bulb type solder pumps, and motor driven vacuum solder
rework stations (pricey).

See the document: "Troubleshooting and Repair of Consumer Electronics
Equipment" for additional info on desoldering of electronic components.

  5.9) Soldering pins in plastic connectors

The thermoplastic used to mold many common cheap connectors softens or
melts at relatively low temperatures.  This can result in the pins popping
out or shifting position (even shorting) as you attempt to solder to them
to replace a bad connection, for example.

One approach that works in some cases is to use the mating socket to stabilize
the pins so they remain in position as you solder.  The plastic will still
melt - not as much if you use an adequately sized iron since the socket will
act as a heat sink - but will not move.

An important consideration is using the proper soldering iron.  In some
cases, a larger iron is better - you get in and out more quickly without
heating up everything in the neighborhood.

  5.10) Solderless connectors

Most internal connections in small appliances are made using solderless
connectors.  These include twist on WireNuts(tm) and crimped terminal lugs
of various sizes and configurations.

WireNuts allow multiple wires to be joined by stripping the ends and then
'screwing' an insulated thimble shaped plastic nut onto the grouped ends
of the wires.  A coiled spring (usually) inside tightly grips the bare
wires and results in a mechanically and electrically secure joint.  For
appliance repair, the required WireNuts will almost always already be
present since they can usually be reused.  If you need to purchase any,
they come in various sizes depending on the number and size of the wires
that can be handled.  It is best to twist the individual conductor strands
of each wire together and then twist the wires together slightly before
applying the WireNut.

Crimped connectors, called lugs, are very common in small appliances.  One
reason is that it is easier, faster, and more reliable, to make connections
using these lugs with the proper crimping equipment than with solder.

A lug consists of a metal sleeve which gets crimped over one or more wires,
an insulating sleeve (usually, not all lugs have these), and a terminal
connection: ring, spade, or push-on are typical.

Lugs connect one or more wires to the fixed terminals found on switches,
motors, thermostats, and so forth.

There are several varieties:

* Ring lugs - the end looks like an 'O' and must be installed on a threaded
  terminal of similar size to the opening in the ring.  The screw or nut must
  be removed to replace a ring lug.

* Spade lugs - the end looks like a 'U' and must be installed on a threaded
  terminal of similar size to the opening in the spade.  These can be slipped
  on and off without entirely removing the screw or nut.

* Push-on lugs - called 'FastOns' by one manufacturer.  The push-on terminal
  makes a tight fit with a (usually) fixed 'flag'.  There may also be a latch
  involved but usually just a pressure fit keeps the connection secure.
  However, excessive heat over time may weaken these types of connections,
  resulting in increased resistance, additional heating, and a bad connection
  or melt-down.

The push-on variety are most common in small appliances.

In the factory, the lugs are installed on the wires with fancy expensive
equipment.  For replacements, an inexpensive crimping tool and an assortment
of lugs will suffice.  The crimping tool looks like a pair of long pliers
and usually combines a wire stripper and bolt cutter with the crimping
function.  It should cost about $6-10.

The crimping tool 'squashes' the metal sleeve around the stripped ends of the
wires to be joined.  A proper crimp will not come apart if an attempt is made
to pull the wires free - the wires will break somewhere else first.  It is
gas-tight - corrosion (within reason) will not affect the connection.

Crimping guidelines:

* Use the proper sized lug.  Both the end that accepts the wire(s) and the
  end that screws or pushes on must be sized correctly.  Easiest is to
  use a replacement that is identical to the original.  Where this is not
  possible, match up the wire size and terminal end as closely as possible.
  There will be a minimum and maximum total wire cross sectional area that
  is acceptable for each size.  Avoid the temptation to trim individual
  conductor strands from wires that will not fit - use a larger size lug.
  Although not really recommended, the bare wires can be doubled over to
  thicken them for use with a lug that is slightly oversize.

* For heating appliances, use only high temperature lugs.  This will assure
  that the connections do not degrade with repeated temperature cycles.
* Strip the wire(s) so that they fit into the lug with just a bit showing
  out the other (screw or push-on) end.  Too long and your risk interference
  with the terminals and/or shorting to other terminals.  Too short and it
  is possible that one or more wires will not be properly positioned, will
  not be properly crimped, and may pull out or make a poor connection.  The
  insulation of the wires should be within the insulating sleeve - there
  should be no bare wire showing behind the lug.

* Crimp securely but don't use so much force that the insulating sleeve
  or metal sleeve is severed.  Usually 1 or 2 crimps for the actual wire
  connection and 1 crimp to compress the insulating sleeve will be needed.

* Test the crimp when complete - there should be no detectable movement of
  the wires.  If there is, you didn't crimp hard enough or the lug is
  too large for your wires.

  5.11) Wire stripping

In order to make most connections, the plastic or other insulating covering
must be removed to expose the bare copper conductors inside.  The best
way to do this is with a proper wire stripper which is either adjustable
or has dedicated positions for each wire size.  It is extremely important
that the internal conductor (single wire or multiple strands) are undamaged.
Nicks or loss of some strands reduces the mechanical and electrical integrity
of the connection.  In particular, a seriously nicked wire may break off
at a later time - requiring an additional repair or resulting in a safety
hazard or additional damage.  The use of a proper wire stripper will greatly
minimize such potential problems.

A pen knife or Xacto knife can be used in a pinch but a wire stripper is
really much much easier.

  5.12) Attaching wires to screw terminals

Screw terminals are often seen in appliances.  In most cases, lugs are
used to attach one or more wires to each terminal and when properly done,
this usually is the best solution.  However, in most cases, you can attach
the wire(s) directly if a lug is not available:

1. The best mechanical arrangement is to put the wire under a machine screw
   or nut, lock washer, and flat washer.  However, you will often see just
   the screw or nut (as in a lamp switch or wall socket).  For most
   applications, this is satisfactory.

2. Avoid the temptation to put multiple wires around a single terminal
   unless you separate each one with a flat washer.

3. Strip enough of the wire to allow the bare wire to be wrapped once around
   the terminal.  To much and some will poke out and might short to something;
   too little and a firm mechanical joint and electrical connection may be

4. For multistranded wire, tightly twist the strands of stripped wire together
   in a clockwise direction as viewed from the wire end.

5. Wrap the stripped end of the wire **clockwise** around the terminal post
   (screw or stud) so that it will be fully covered by the screw head, nut,
   or flat washer.  This will insure that the wire is grabbed as the screw
   or nut is tightened.  A pair of small needlenose pliers may help.

6. Hold onto the wire to keep it from being sucked in as the screw or nut
   is tightened.  Don't overdo it - you don't need to sheer off the head
   of the screw to make a secure reliable connection.

7. Inspect the terminal connection: the bare wire should be fully covered
   by the head of the screw, nut, or flat washer.  Gently tug on the wire
   to confirm that it is securely fastened.

  5.13) Test equipment

Very little test equipment is needed for most household appliance repair.

First, start with some analytical thinking.  Many problems associated
with household appliances do not require a schematic.  Since the internal
wiring of many appliances is so simple, you will be able to create your
own by tracing the circuits in any case.  However, for more complex
appliances, a schematic may be useful as wires may run behind and under
other parts and the operation of some custom switches may not obvious.
The causes for the  majority of problems will be self evident once you gain
access to the interior - loose connections or broken wires, bad switches,
open heating element, worn motor brushes, dry bearings.  All you will need
are some basic hand tools, a circuit and continuity tester, light oil and
grease, and your powers of observation (and a little experience).  Your
built in senses and that stuff between your ears represents the most
important test equipment you have.

The following will be highly desirable for all but the most obvious problems:

1. Circuit tester (neon light) - This is used to test for AC power or confirm
   that it is off.  For safety, nothing can beat the simplicity of a neon
   tester.   Its use is foolproof as there are no mode settings or range
   selections to contend with.  Touch its two probes to a circuit and if it
   lights, there is power.  (This can also take the place of an Outlet
   tester but it is not as convenient (see below).  Cost: $2-$3.

2. Outlet tester (grounds and miswiring) - This will confirm that a 3 prong
   outlet is correctly wired with respect to Hot, Neutral, and Ground.  While
   not 100% assured of correct wiring if the test passes, the screwup would
   need to be quite spectacular.  This simple device instantly finds missing
   Grounds and interchanged Hot and Neutral - the most common wiring mistakes.
   Just plug it into an outlet and if the proper two neon light are lit at
   full brightness, the outlet is most likely wired correctly.  Cost: about $6.

   These are just a set of 3 neon bulbs+resistors across each pair of wires.
   If the correct bulbs light at full brightness - H-N, H-G - then the
   circuit is likely wired correctly.  If the H-G light is dim or out or
   if both the H-G and G-N are dim, then you have no ground.  If the N-G
   light is on and the H-G light is off, you have reversed H and N, etc.

   What it won't catch: Reversed N and G (unlikely unless someone really
   screwed up) and marginal connections (since the neon bulbs doesn't use much
   current).  It also won't distinguish between 110 VAC and 220 VAC circuits
   except that the neon bulbs will glow much brighter on 220 VAC but without
   a direct comparison, this could be missed.

   For something that appears to test for everything but next week's weather:

   (From: Bill Harnell (bharne@adss.on.ca)).

   Get an ECOS 7105 tester! (ECOS Electronics Corporation, Oak Park, Illinois,
   708-383-2505).  Not cheap, however.  It sold for $59.95 in 1985 when I
   purchased somewhere around 600 of them for use by our Customer Engineers
   for safety purposes!

   It tests for:

   Correct wiring, reversed polarity, open Ground, open Neutral, open Hot,
   Hot & Ground reversed, Hot on neutral, Hot unwired, other errors,
   over voltage (130 VAC+), under voltage (105 VAC-), Neutral to Ground short,
   Neutral to Ground reversal, Ground impedance test (2 Ohms or less ground
   impedance - in the equipment ground conductor).

   Their less expensive 7106 tester performs almost all of the above tests.

   FWIW, I have no interest in the ECOS Corporation of any kind. Am just a
   very happy customer.

3. Continuity tester (buzzer or light) - Since most problems with appliances
   boil down to broken connections, open heating elements, defective switches,
   shorted wires, and bad motor windings, a continuity tester is all that
   is needed for most troubleshooting.  A simple battery operated buzzer or
   light bulb quickly identifies problems.  If a connection is complete, the
   buzzer will sound or the light will come on.  Note that a dedicated
   continuity tester is preferred over a similar mode on a multimeter because
   it will operate only at very low resistance.  The buzzer on a multimeter
   sounds whenever the resistance is less than about 200 ohms - a virtual open
   circuit for much appliance wiring.

   A continuity tester can be constructed very easily from an Alkaline
   battery, light bulb or buzzer, some wire, and a set of test leads with
   probes.  All of these parts are available at Radio Shack.

                     AA, C, or D cell    1.5 V flashlight bulb or buzzer
                            +|  -             +------------------+
   Test probe 1  o-----------| |--------------|  Bulb or buzzer  |-------+ 
                             |                +------------------+       |
   Test probe 2  o-------------------------------------------------------+

   CAUTION: Do not use this simple continuity tester on electronic equipment
   as there is a slight possibility that the current provided by the battery
   will be too high and cause damage.  It is fine for most appliances.

4. GFCI tester - outlets installed in potentially wet or outdoor areas should
   be protected by a Ground Fault Circuit Interrupter (GFCI).  A GFCI is now
   required by the NEC (Code) in most such areas.  This tester will confirm
   that any outlets protected by a GFCI actually will trip the device if there
   is a fault.  It is useful for checking the GFCI (though the test button
   should do an adequate job of this on its own) as well as identifying or
   testing any outlets downstream of the GFCI for protection.

   Wire a 3 prong plug with a 15 K ohm 1 W resistor between H and G.  Insulate
   and label it!  This should trip a GFCI protected outlet as soon as it is
   plugged in since it will produce a fault current of about 7 mA.

   Note that this device will only work if there is an actual Safety Ground
   connection to the outlet being tested.  A GFCI retrofitted into a 2 wire
   installation without a Ground cannot be tested in this way since a GFCI
   does not create a Ground.  However, jumpering this rig between the H and
   and a suitable earth ground (e.g., a cold water in an all copper plumbing
   system) should trip the GFCI.  Therefore, first use an Outlet Tester
   (above) to confirm that there is a Safety Ground present.

   The test button works because it passes an additional current through the
   sense coil between Hot and Neutral tapped off the wiring at the line side
   of the GFCI and therefore doesn't depend on having a Ground.

5. Multimeter (VOM or DMM) - This is necessary for actually measuring
   voltages and resistances.  Almost any type will do - even the $14.95
   special from Sears.  Accuracy is not critical for household appliance
   repair but reliability is important - for your safety if no other
   reason.  It doesn't really matter whether it is a Digital MultiMeter (DMM)
   or analog Volt Ohm Meter (VOM).  A DMM may be a little more robust should
   you accidentally put it on an incorrect scale.  However, they both serve
   the same purpose.  A cheap DMM is also not necessarily more accurate than
   a VOM just because it has digits instead of a meter needle.  A good quality
   well insulated set of test leads and probes is essential.  What comes with
   inexpensive multimeters may be too thin or flimsy.  Replacements are
   available.  Cost: $15-$50 for a multimeter that is perfectly adequate for
   home appliance repair.

   Note: For testing of household electrical wiring, a VOM or DMM can indicate
   voltage between wires which is actually of no consequence.  This is due to
   the very high input resistance/impedance of the instrument.  The voltage
   would read zero with any sort of load.  See the section: "Phantom voltage
   measurements of electrical wiring".

Once you get into electronic troubleshooting, an oscilloscope, signal
generator, and other advanced (and expensive) test equipment will be useful.
For basic appliance repair, such equipment would just gather dust.

  5.14) Getting inside consumer electronic equipment

Yes, you will void the warranty, but you knew this already.

Appliance manufacturers seem to take great pride in being very mysterious
as to how to open their equipment.  Not always, but this is too common
to just be a coincidence.

A variety of techniques are used to secure the covers on consumer
electronic equipment:

1. Screws.  Yes, many still use this somewhat antiquated technique.
   Sometimes, there are even embossed arrows on the case indicating
   which screws need to be removed to get at the guts.  In addition to
   obvious screw holes, there may be some that are only accessible when a
   battery compartment is opened or a trim panel is popped off.

   These are almost always of the Philips variety though more and more
   appliances are using Torx or security Torx type screws.  Many of these
   are hybrid types - a slotted screwdriver may also work but the Philips
   or Torx is a whole lot more convenient.

   A precision jeweler's  screwdriver set including miniature Philips
   head drivers is a must for repair of miniature portable devices.

2. Hidden screws.  These will require prying up a plug or peeling off
   a decorative decal.  It will be obvious that you were tinkering - it
   is virtually impossible to put a decal back in an undetectable way.
   Sometimes the rubber feet can be pryed out revealing screw holes.  For
   a stick-on label, rubbing your finger over it may permit you to locate
   a hidden screw hole.  Just puncture the label to access the screw as this
   may be less messy then attempting to peel it off.

3. Snaps.  Look around the seam between the two halves.  You may (if you are
   lucky) see points at which gently (or forcibly) pressing with a screwdriver
   will unlock the covers.  Sometimes, just going around the seam with a butter
   knife will pop the cover at one location which will then reveal the
   locations of the other snaps.

4. Glue.  Or more likely, the plastic is fused together.  This is particularly
   common with AC adapters (wall warts).  In this case, I usually carefully
   go around the seam with a hacksaw blade taking extreme care not to go
   through and damage internal components.  Reassemble with plastic electrical

5. It isn't designed for repair.   Don't laugh.  I feel we will see more
   and more of this in our disposable society.  Some devices are totally
   potted in Epoxy and are 'throwaways'.  With others, the only way to open
   them non-destructively is from the inside.

Don't force anything unless you are sure there is no alternative - most
of the time, once you determine the method of fastening, covers will
come apart easily.  If they get hung up, there may be an undetected
screw or snap still in place.

When reinstalling the screws, first turn them in a counter-clockwise direction
with very slight pressure. You will feel them "click" as they fall into the
already formed threads.  Gently turn clockwise and see if they turn easily.
If they do not, you haven't hit the previously formed threads - try again.
Then just run them in as you normally would. You can always tell when you
have them into the formed threads because they turn very easily for nearly
the entire depth.  Otherwise, you will create new threads which will quickly
chew up the soft plastic.  Note: these are often high pitch screws - one turn
is more than one thread - and the threads are not all equal.

The most annoying (to be polite) situation is when after removing the
18 screws holding the case together (losing 3 of them entirely and mangling
the heads on 2 others), removing three subassemblies, and two other circuit
boards, you find that the adjustment you wanted was accessible through a
hole in the case just by partially peeling back a rubber hand grip! (It
has happened to me).

When reassembling the equipment make sure to route cables and other wiring
such that they will not get pinched or snagged and possibly broken or have
their insulation nicked or pierced and that they will not get caught in
moving parts.  This is particularly critical for AC line operated appliances
and those with motors to minimize fire and shock hazard and future damage
to the device itself.  Replace any cable ties that were cut or removed during
disassembly and add additional ones of your own if needed.  Some electrical
tape may sometimes come in handy to provide insulation insurance as well.
As long as it does not get in the way, additional layers of tape will not
hurt and can provide some added insurance against future problems.  I often
put a layer of electrical tape around connections joined with WireNuts(tm)
as well just to be sure that they will not come off or that any exposed wire
will not short to anything.

  5.15) Getting built up dust and dirt out of a equipment

This should be the first step in any inspection and cleaning procedure.

Appliances containing fans or blowers seem to be dust magnets - an incredible
amount of disgusting fluffy stuff can build up in a short time - even with
built-in filters.

Use a soft brush (like a new cheap paint brush) to remove as much dirt,
dust, and crud, as possible without disturbing anything excessively.  Some
gentle blowing (but no high pressure air) may be helpful in dislodged
hard to get at dirt - but wear a dust mask.

Don't use compressed air on intricate mechanisms, however, as it might
dislodge dirt and dust which may then settle on lubricated parts and 
contaminating them.  High pressure air could move oil or grease from where
it is to where it should not be.  If you are talking about a shop air
line, the pressure may be much much too high and there may be contaminants
as well.

A Q-tip (cotton swab) moistened with politically correct alcohol can be used
to remove dust and dirt from various hard to get at surfaces.

  5.16) Lubrication of appliances and electronic equipment

The short recommendation is: Don't add any oil or grease unless you are
positively sure it is needed.  Most parts are lubricated at the factory and do
not need any further lubrication over their lifetime.  Too much lubrication is
worse then too little.  It is easy to add a drop of oil but difficult and time
consuming to restore a tape deck that has taken a swim.

NEVER, ever, use WD40!  WD40 is not a good lubricant despite the claims on the
label.  Legend has it that the WD stands for Water Displacer - which is one of
the functions of WD40 when used to coat tools for rust prevention.  WD40 is
much too thin to do any good as a general lubricant and will quickly collect
dirt and dry up.  It is also quite flammable and a pretty good solvent - there
is no telling what will be affected by this.

A light machine oil like electric motor or sewing machine oil should be
used for gear or wheel shafts.  A plastic safe grease like silicone grease
or Molylube is suitable for gears, cams, or mechanical (piano key) type
mode selectors.  Never use oil or grease on electrical contacts.

One should also NOT use a detergent oil.  This includes most automotive
engine oils which also have multiple additives which are not needed and are
undesirable for non-internal combustion engine applications.

3-In-One(tm) isn't too bad if that is all you have on hand and the future of
the universe depends on your fan running smoothly.  However, for things that
don't get a lot of use, it may gum up over time.  I don't know whether it
actually decomposes or just the lighter fractions (of the 3) evaporate.

Unless the unit was not properly lubricated at the factory (which is quite
possible), don't add any unless your inspection reveals the specific need.
Sometimes you will find a dry bearing, motor, lever, or gear shaft.  If
possible, disassemble and clean out the old lubricant before adding fresh
oil or grease.

Note that in most cases, oil is for plain bearings (not ball or roller)
and pivots while grease is used on sliding parts and gear teeth.

In general, do not lubricate anything unless you know there is a need.
Never 'shotgun' a problem by lubricating everything in sight!  You might
as well literally use a shotgun on the equipment!

  5.17) Common appliance problems

Despite the wide variety of appliances and uses to which they are put,
the vast majority of problems are going to be covered in the following
short list:

1. Broken wiring inside cordset - internal breaks in the conductors of
   cordsets or other connecting cords caused by flexing, pulling, or
   other long term abuse.  This is one of the most common problem with
   vacuum cleaners which tend to be dragged around by their tails.

   Testing: If the problem is intermittent, (or even if it is not), plug
   the appliance in and turn it on.  Then try bending or pushing the wire
   toward the plug or appliance connector end to see if you can make the
   internal conductors touch at least momentarily.  Ii the cordset is
   removable, test between ends with a continuity checker or multimeter
   on the low ohms scale.  If it is not detachable, open the appliance to
   perform this test.

2. Bad internal connections - broken wires, corroded or loosened terminals.
   Wires may break from vibration, corrosion, poor manufacturing, as
   well as thermal fatigue.  The break may be in a heating element or
   other subassembly.  In many cases, failure will be total as in
   when one of the AC line connections falls off.  At other times,
   operation will be intermittent or erratic - or parts of the appliance
   will not function.  For example, with a blow dryer, the heating element
   could open up but the fan may continue to run properly.

   Testing: In many cases, a visual inspection with some careful flexing
   and prodding will reveal the location of the bad connection.  If it is
   an intermittent, this may need to be done with a well insulated stick
   while the appliance is on and running (or attempting to run).  When
   all else fails, the use of a continuity checker or multimeter on the
   low ohms scale can identify broken connections which are not obviously
   wires visibly broken in two.  For testing heating elements, use the
   multimeter as a continuity checker may not be sensitive enough since
   the element normally has some resistance.

3. Short circuits.  While much less frequent than broken or intermittent
   connections, two wires touching or contacting the metal case of an
   appliance happens all too often.  Partially, this is due to the shoddy
   manufacturing quality of many small appliances like toaster ovens.  These
   also have metal (mostly) cabinets and many metal interior parts with
   sharp edges which can readily eat through wire insulation due to repeated
   vibrations, heating and cooling cycles, and the like.  Many appliances
   are apparently designed by engineers (this is being generous) who do not
   have any idea of how to build or repair them.  Thus, final assembly, for
   example, must sometimes be done blind - the wires get stuffed in and covers
   fastened - which may end up nicking or pinching wires between sharp metal
   parts.  The appliance passes the final inspection and tests but fails down
   the road.

   A short circuit may develop with no operational problems - but the case
   of the appliance will be electrically 'hot'.  This is a dangerous situation.
   Large appliances with 3 wire plugs - plugged into a properly grounded 3 wire
   circuit - would then blow a fuse or trip a circuit breaker.  However, small
   appliances like toaster, broilers, irons, etc., have two wire plugs and
   will just set there with a live cabinet.

   Testing: Visually inspect for bare wires or wires with frayed or worn
   insulation touching metal parts, terminals they should not be connected
   to, or other wires.  Use a multimeter on the high ohms scale to check
   between both prongs of the AC plug and any exposed metal parts.  Try all
   positions of any power or selector switches.  Any resistance measurement
   less than 100K ohms or so is cause for concern - and further checking.
   Also test between internal terminals and wires that should not be connected

   Too many people like to blame everything from blown light bulbs to
   strange noises on short circuits.  A 'slight', slow, or marginal short
   circuit is extremely rare.  Most short circuits in electrical wiring
   between live and neutral or ground (as opposed to inside appliances
   where other paths are possible) will blow a fuse or trip a breaker.  Bad
   connections (grounds, neutral, live), on the other hand, are much much
   more common.

4. Worn, dirty, or broken switches or thermostat contacts.  These will
   result in erratic or no action when the switch is flipped or thermostat
   knob is turned.  In many cases, the part will feel bad - it won't have
   that 'click' it had when new or may be hard to turn or flip.  Often,
   however, operation will just be erratic - jiggling the switch or knob
   will make the motor or light go on or off, for example.

   Testing: Where there is a changed feel to the switch or thermostat with
   an associated operational problem, there is little doubt that the part
   is bad and must be replaced.  Where this is not the case, label the
   connections to the switch or thermostat and then remove the wires.  Use
   the continuity checker or ohmmeter across each set of contacts.  They
   should be 0 ohms or open depending on the position of the switch or knob
   and nothing in between.  In most cases, you should be able to obtain
   both readings.  The exception is with respect to thermostats where room
   temperature is off one end of their range.  Inability to make the contacts
   open or close (except as noted above) or erratic intermediate resistances
   which are affected by tapping or jiggling are a sure sign of a bad set of

5. Gummed up lubrication, or worn or dry bearings.  Most modern appliances
   with motors are supposedly lubricated for life.  Don't believe it!  Often,
   due to environmental conditions (dust, dirt, humidity) or just poor quality
   control during manufacture (they forgot the oil), a motor or fan bearing
   will gum up or become dry resulting in sluggish and/or noisy operation
   and overheating.  In extreme cases, the bearing may seize resulting in
   a totally stopped motor.  If not detected, this may result in a blown
   fuse (at the least) and possibly a burnt out motor from the overheating.

   Testing: If the appliance does not run but there is a hum (AC line
   operated appliances) or runs sluggishly or with less power than you 
   recall when new, lubrication problems are likely.  With the appliance
   unplugged, check for free rotation of the motor(s).  In general, the
   shaft sticking out of the motor itself should turn freely with very
   little resistance.  If it is difficult to turn, the motor bearings
   themselves may need attention or the mechanism attached to the motor
   may be filled with crud.  In most cases, a thorough cleaning to remove
   all the old dried up and contaminated oil or grease followed by relubing
   with similar oil or grease as appropriate will return the appliance to
   good health.  Don't skimp on the disassembly - total cleaning will be
   best.  Even the motor should be carefully removed and broken down to
   its component parts - end plates, rotor, stator, brushes (if any) in
   order to properly clean and lubricate its bearings.  See the appropriate
   section of the chapter: "Motors 101" for the motor type in your appliance.

6. Broken or worn drive belts or gears - rotating parts do not rotate
   or turn slowly or with little power even through the motor is revving
   its little head off.  When the brush drive belt in an upright vacuum
   cleaner breaks, the results are obvious and the broken belt often falls
   to the ground (to be eaten by the dog or mistaken for a mouse tail - Eeek!)
   However, there are often other belts inside appliances which will result
   in less obvious consequences when they loosen with age or fail completely.

   Testing: Except for the case of a vacuum cleaner where the belt is readily
   accessible, open the appliance (unplugged!).  A good rubber belt will be
   perfectly elastic and will return to its relaxed length instantly when
   stretched by 25 percent and let go.  It will not be cracked, shiny, hard,
   or brittle.  A V-type belt should be dry (no oil coating), undamaged (not
   cracked, brittle, or frayed), and tight (it should deflect 1/4" to 1/2"
   when pressed firmly halfway between the pulleys).

   Sometimes all that is needed is a thorough cleaning with soap and water
   to remove accumulated oil or grease.  However, replacement will be required
   for most of these symptoms.  Belts are readily available and an exact
   match is rarely essential.

7. Broken parts - plastic or metal castings, linkages, washers, and other
   'doodads' are often not constructed quite the way they used to be.  When
   any of these fail, they can bring a complicated appliance to its knees.
   Failure may be caused by normal wear and tear, improper use (you tried
   to vacuum nuts and bolts just like on TV), accidents (why was your 3
   year old using the toaster oven as a step stool?), or shoddy manufacturing.

   Testing: In many cases, the problem will be obvious.  Where it is not,
   some careful detective work - putting the various mechanisms through
   their paces - should reveal what is not functioning.  Although replacement
   parts may be available, you can be sure that their cost will be excessive
   and improvisation may ultimately be the best approach to repair.  See
   the section: "Fil's tips on improvised parts repair".

8. Insect damage.  Many appliance make inviting homes for all sort of multi-
   legged creatures.  Evidence of their visits or extended stays will be
   obvious including frayed insulation, short circuits caused by bodily
   fluids or entire bodies, remains of food and droppings.  Even the smallest
   ventilation hole can be a front door.

   The result may be any of the items listed in (1) to (7) above.  Once the
   actual contamination has been removed and the area cleaned thoroughly,
   inspect for damage and repair as needed.  If the appliance failed while
   powered, you may also have damage to wiring or electronic components due
   to any short circuits that were created by the intruders' activities.

Chapter 6) Types of Parts Found in Small Appliances

  6.1) So many, so few

While there are an almost unlimited variety of small appliances and power
tools, they are nearly all constructed from under two dozen basic types
of parts.  And, even with these, there is a lot of overlap.

The following types of parts are found in line powered appliances:

        * Cordsets - wire and plug.
        * Internal wiring - cables and connectors.
        * Switches - power, mode, or speed selection.
        * Relays - electrically activated switches for power or control.
        * Electrical overload protection devices - fuses and circuit breakers.
        * Thermal protection devices - thermal fuses and thermal switches.
        * Controls 1 - adjustable thermostats and humidistats.
        * Controls 2 - rheostats and potentiometers.
        * Interlocks - prevent operation with case or door open.
        * Light bulbs - incandescent and fluorescent.
        * Indicators - incandescent or neon light bulbs or LEDs.
        * Heating elements - NiChrome coils or ribbon, Calrod, Quartz.
        * Solenoids - small and large.
        * Small electronic components - resistors, capacitors, diodes.
        * Motors - universal, induction, DC, timing.
        * Fans and Blowers - bladed or centrifugal.
        * Bearings and bushings.
        * Mechanical controllers - timing motors and cam switches.
        * Electronic controllers - simple delay or microprocessor based.

Battery and AC adapter powered appliance use most of the same types of
parts but they tend to be smaller and lower power than their line powered
counterparts.  For example, motors in line powered devices tend to be
larger, more powerful, and of different design (universal or induction
compared to permanent magnet DC type).  So, we add the following:

        * Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-acid.
        * AC adapters and chargers - wall 'warts' with AC or DC outputs.

The only major category of devices that these parts do not cover are gas
discharge lamps and lighting fixtures (fluorescent, neon, mercury, and
sodium), which we will discuss in a separate chapters.

  6.2) Cordsets - wire and plug

A 'cordset' is a combination of the cord consisting of 2 or 3 insulated wires
and a plug with 2 or 3 prongs.  Cord length varies from 12 inches (or less)
for some appliances like toasters to 25 feet or more for vacuum cleaners.
Most common length is 6-8 feet.  The size of the wire and type of insulation
also are important in matching a replacement cordset to an appliance.

Most plug-in appliances in the U.S. will have one of 3 types of line cord/plug

1. Non-polarized 2 prong.  The 2 prongs are of equal width so the plug
   may be inserted in either direction.  These are almost universal
   on older appliances but may be found on modern appliances as well 
   which are double insulated or where polarity does not matter.  (Note:
   it **must** not matter for user safety in any case.  The only time it can
   matter otherwise is with respect to (1) possible RFI (Radio Frequency
   Interference) generation or (2) service safety (this would put the
   center contact of a light bulb socket or internal switch and fuse on
   the Hot wire).

2. Polarized 2 prong.  The prong that is supposed to be plugged into
   the Neutral slot of the outlet is wider.  All outlets since sometime
   around the 1950s (???) have been constructed to accept polarized plugs
   only one way.  While no appliance should ever be designed where the
   way it is plugged in can result in a user safety hazard, a lamp socket
   where the shell - the screw thread part - is plugged into Neutral is
   less hazardous when changing a light bulb.  In addition, when servicing
   a small appliance with the cover removed, the Hot wire with a polarized
   plug should go to the switch and fuse and thus most of the circuitry will
   be disconnected with the switch off or fuse pulled.

3. Grounded 3 prong.  In addition to Hot and Neutral, a third grounding
   prong is provided to connect the case of the equipment to safety Ground.
   This provides added protection should internal wiring accidentally short
   to a user accessible metal cabinet or control.  In this situation, the
   short circuit will (or is supposed to) blow a fuse or trip a circuit
   breaker or GFCI rather than present a shock hazard.  DO NOT just cut
   off the third prong if your outlet does not have a hole for it.  Have
   the outlet replaced with a properly grounded one (which may require
   pulling a new wire from the service panel).  As a short term solution,
   the use of a '3 to 2' prong adapter is acceptable IF AND ONLY IF the
   outlet box is securely connected to safety Ground already (BX or Romex
   cable with ground).  Grounding also is essential for surge suppressors
   to operate properly (to the extent that they ever do) and may reduce
   RFI susceptibility and emissions if line filters are included (as with
   computer equipment and consumer electronics).  Power conditioners require
   the Ground connection for line filtering as well.

Each of these may be light duty (less than 5 Amps or 600 Watts), medium
duty (8 A or 1000 W) or heavy duty (up to 15 A or 1800 W).  The rating is
usually required to be stamped on the cord itself or on a label attached
to the cord.  Thickness of the cord is not a reliable indication of its
power rating!  (Note: U.S. 115 VAC 15 amp circuits are assumed throughout
this document unless otherwise noted.)

Light duty cordsets are acceptable for most appliances without high power
heating elements or heavy duty electric motors.  These include table lamps,
TVs, VCRs, stereo components, computers, dot matrix and inkjet printers,
thermal fax machines, monitors, fans, can openers, etc.  Electric blankets,
heating pads, electric brooms, and food mixers are also low power and light
duty cordsets are acceptable.  The internal wires used is #18 AWG which is
the minimum acceptable wire size (highest AWG number) for any AC line powered

Medium or heavy duty cordsets are REQUIRED for heating appliances like
electric heaters (both radiant and convection), toasters, broilers, steam and
dry irons, coffee makers and electric kettles, microwave and convection ovens,
laser printers, photocopiers, Xerographic based fax machines, canister and
upright vacuum cleaners and shop vacs, floor polishers, many portable and
most stationary power tools.  The internal wires used will be #16 AWG (medium
duty) or #14 AWG (heavy duty).

For replacement, always check the nameplate amps or wattage rating and use
a cordset which has a capacity at least equal to this.  The use of an
inadequate cordset represents a serious fire hazard.

Three prong grounded cordsets are required for most computer equipment,
heavy appliances, and anything which is not double insulated and has metal
parts that may be touched in normal operation (i.e., without disassembly).

The individual wires in all cordsets except for unpolarized types (e.g., lamp
cord) will be identified in some way.  For sheathed cables, color coding is
used.   Generally, in keeping with the NEC (Code), black will be Hot, white
will be Neutral, and green will be Safety Ground.  You may also find brown for
Hot, blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances and
electronic equipment.

For zip cord with a polarized plug, one of the wires will be tagged with with
a colored thread or a ridge on the outer insulation to indicate which is the
Neutral wire.  For unpolarized types like lamp cord, no identification is
needed (though there still may be some) as the wires and prongs of the plug are

In general, when replacement is needed, use the same configuration and
length and a heavy duty type if the original was heavy duty.  Substituting
a heavy duty cordset for a light duty one is acceptable as long as the
additional stiffness is acceptable in terms of convenience.  A shorter
cord can usually be used if desired.  In most cases, a longer cord (within
reason) can be substituted as well.  However, performance of heavy duty
high current high wattage appliances may suffer if a really long cord (or
extension cord) is used voltage drop from the wire resistance.  For a modest
increase in length, use the next larger wire size (heavy duty instead of
medium duty, #14 instead of #16, for example).

Before disconnecting the old cord, label connections or make a diagram and
then match the color code or other wire identifying information.  In all cases,
it is best to confirm your final wiring with a continuity tester or multimeter
on the low ohms scale.  Mistakes on your part or the manufacturer of the new
cord are not unheard of!

Common problems: internal wiring conductors broken at flex points (appliance
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a broken connection.

Testing: Appliance cordsets can always be tested with a continuity checker or
multimeter on a the low ohms scale.

* Squeeze, press, spindle, fold, mutilate the cord particularly at both ends
  as while testing to locate intermittent problems.

* If you are too lazy to open the appliance (or this requires the removal of
  29 screws), an induction type of tester such as used to locate breaks in
  Christmas tree light strings can be used to confirm continuity by plugging
  the cord in both ways and checked along its length to see if a point of
  discontinuity can be located.

  (From: Brian Symons (brians@mackay.net.au)).

  A permanent bench setup with a pair of outlets (one wired with reverse
  polarity marked: FOR TESTING ONLY) can be provided to facilitate connecting
  to either of the wires of the cordset when using an induction type tester.

Note: broken wires inside the cordset at either the plug or appliance end
are among the most common causes of a dead vacuum cleaner due to abuse
it gets - being tugged from the outlet, vacuum being dragged around by
the cord, etc.  Many other types of appliances suffer the same fate.
Therefore, checking the cord and plug should be the first step in
troubleshooting any dead appliance.

If the cord is broken at the plug end, the easiest thing to do is to
replace just the plug.  A wide variety of replacement plugs are available
of three basic types: clamp-on/insulation piercing, screw terminals,
and wire compression.

Clamp-on/insulation piercing plugs are installed as follows:  First, the
cord is cleanly cut but not stripped and inserted into the body of the
plug.  A lid or clamping bar is then closed which internally pierces the
insulation and makes contact with the prongs.  When used with the proper
size wire, these are fairly reliable for light duty use - table lamps
and other low power appliances.  However, they can lead to problems of
intermittent or bad connections if the wire insulation thickness does not
precisely match what the plug expects.

Plugs with screw terminals make a much more secure robust connections but
require a bit more time and care in assembly to assure a proper connection
and avoid stray wire strands causing short circuits or sticking out and
representing a shock hazard.  Tightly twist the strands of the stripped
wire together before wrapping around the screw in a clockwise direction
before tightening.  Don't forget to install the fiber insulator that is
usually supplied with the plug.

The best plugs have wire clamp terminals.  The stripped end of the wire
is inserted into a hole and a screw is tightened to clamp the wire in
place.  Usually, a molded plastic cover is then screwed over this assembly
and includes a strain relief as well.  These are nearly foolproof and
consequently are used in the most demanding industrial and medical
applications.  They are, not surprisingly, also typically the most

Where damage is present at the appliance end of the cord, it may be possible
to just cut off the bad portion and reinstall what remains inside of the
appliance.  As long as this is long enough and a means can be provided for
adequate strain relief, this is an acceptable alternative to replacement of
the entire cordset.

  6.3) Appliance cord gets hot

This applies to all high current appliances, not just space heaters though
these are most likely to be afflicted since they are likely to be run for
extended periods of time.

Of course, if the problem is with an *extension* cord, then either it is
overloaded or defective.  In either case, the solution should be obvious.

Some cords will run warm just by design (or cheapness in design using
undersized conductors).

However, if it is gets hot during use, this is a potential fire hazard.

If it is hot mainly at the plug end - get a heavy duty replacement plug - one
designed for high current appliances using screw terminals - at a hardware
store, home center, or electrical supply house.  Cut the cord back a couple
of inches.

If the entire cord gets warm, this is not unusual with a heater.  If it
gets hot, the entire cord should be replaced.  Sometimes with really old
appliance, the copper wires in the cord oxidize even through the rubber
insulation reducing their cross section and increasing resistance.  This
leads to excessive power dissipation in the cord.  Replacement *heavy duty*
cordsets are readily available.

  6.4) Extension cords

We treat extension cords too casually - abusing them and using underrated
extension cords with heavy duty appliances.  Both of these are serious
fire and shock hazards.  In addition, the use of a long inadequate
extension will result in reduced voltage due to resistive losses at the
far end.  The appliance may not work at full capacity and in some cases
may even be damaged by this reduced voltage.

Extension cord rules of use:

1. The capacity must be at least equal to the SUM of the wattages or amperages
   of all the appliances plugged in at the far end.  Larger is fine as well
   and is desirable for long extensions.  Check the rating marked on the cord
   or a label attached to the cord.  Thickness of the outside of the cord is
   not a reliable indication of power rating.

2. Use a type which is the most restrictive of any appliances that will be
   plugged in (e.g., 3 prong if any are of this type, 2 prong polarized
   otherwise unless your outlets are non-polarized (old dwellings).

3. Use only as long an extension as required.  For very long runs, use
   a higher capacity extension even if the power requirements are modest.

4. NEVER run extensions under carpeting as damage is likely and this will
   go undetected.  Never run extensions inside walls.  Add new outlets where
   needed with properly installed building wire (Romex).  This must be done
   in such a way that it meets the National Electric Code (NEC) in your area.
   It may need to be inspected if for no other reason than to guarantee that
   your homeowner's insurance won't give you a hard time should any 'problems'
   arise.  Surface mount outlets and conduit are available to extend the reach
   of existing outlets with minimal construction if adding new ones is
   difficult or too costly.

5. Don't use heavy duty extensions as a long term solution if possible.
   Similarly, don't use extensions with 'octopus' connections - install
   an outlet strip.

Extension cords of any type, capacity, and length can be easily constructed
from components and wire sold at most hardware stores and home centers.  This
is rarely economical for light duty polarized types as these are readily
available and very inexpensive.  However, for heavy duty 3 prong extensions,
a custom constructed one is likely to save money especially if an unusual
length is required.  Making up a heavy duty extension with a 'quad' electrical
box with a pair of 15 amp duplex outlets is a very rugged convenient
alternative to a simple 3 prong socket.

Common problems: internal wiring conductors broken at flex points (socket
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a bad or intermittent

Testing: Extension cords can always be tested with a continuity checker or
multimeter on a the low ohms scale.

  6.5) Determining the location of a break in an extension cord

This isn't worth the time it would take to describe for a $.99 6 foot K-Mart
special but it might make sense for a 100 foot heavy duty outdoor type.  If
the problem is near one end, a couple of feet can be cut off and a new plug
or socket installed.  If more towards the middle, the wires can be cut and
spliced or two smaller cords could be made from the pieces.

But, how do you locate the break?

* Use a Time Domain Reflectometer (TDR).  Oops, don't have one?  And, you
  probably don't even know what this means!  (Basically, a TDR sends a pulse
  down a wire and measures how long it takes for a reflected pulse to return
  from any discontinuities.  The delay is a measure of distance.)  Don't
  worry, there are alternatives :-).

* If there is no obvious damage - you didn't attempt to mow the cord by
  accident - the most likely location is at the end where the plug of socket
  strain relief joins the wire.  Squeezing, squishing, pushing, etc., with the
  cord plugged into a live outlet and lamp or radio plugged into the other end
  may reveal the location by a momentary flash or blast of sound.  

* Try a binary search with a probe attached to a straight pin.  This works
  best with a cord where the wires are easily located - not the round double
  insulated type.  Attach one probe of your multimeter to the prong of the
  plug attached to the broken wire.  Start at the middle with your pin probe.
  If there is continuity move half the distance to the far end.  If it is
  open, move half the distance toward near end.  Then 1/4, 1/8, and so forth.
  It won't take long to located the break this way.  Of course, there will be
  pin holes in the insulation so this is not recommeded for outdoor extension
  cords unless the holes are sealed.

* You may be able to use one of those gadgets for testing Christmas Tree light
  sets - these inexpensive devices sense the AC field in proximity to its
  probe.  Plug the cord in so that the Hot of your AC line is connected to one
  of the wires you know is broken (from testing with an ohmmeter) and run the
  device along the cord until the light changes intensity.

  This also works for appliance cords where you are too lazy to go inside to
  check continuity.  You may need to try both wires in the cord to locate the
  broken one.

* If you have some real test equipment (but not a TDR!) attach the output of
  a frequency generator to the prong of the plug for the wire you know is
  broken.  Use an oscilloscope as a sensor - run the probe along the cord
  until the detected signal abruptly drops in intensity.

  An AM or multiband radio may also be suitable as a detector.

  (From: Asimov (Asimov@juxta.mn.pubnix.ten)).

  Try a capacitance ratio method. Simply measure the capacitance between the
  wires at both ends. The break should be at approximately the same distance
  ratio as that of the two measured capacitances.

  6.6) Internal wiring - cables and connectors

Wiring isn't super glamorous but represents the essential network of roads
that interconnect all of the appliance's internal parts and links it to the
outside world.

Inside the appliance, individual wires (often multicolored to help identify
function) or cables (groups of wires combined together in a single sheath
or bundle) route power and control signals to the various components.  Most
are insulated with plastic or rubber coverings but occasionally you will
find bare, tinned (solder coated), or plated copper wires.  In high temperature
appliances like space heaters and toasters, the insulation (if present) will
be asbestos (older) or fiberglass.  (Rigid uninsulated wires are also commonly
found in such applications.)  Particles flaking off from either of these
materials are a health hazard if you come in contact, inhale, or ingest them.
They are also quite fragile and susceptible to damage which may compromise
their insulating properties so take care to avoid excessive flexing or
repositioning of wires with this type of insulation.  Fiberglass insulation
is generally loose fitting and looks like woven fabric.  Asbestos is light
colored, soft, and powdery.

Color coding will often be used to make keeping track of the wires easier
and to indicate function.  However, there is no standard except for the
input AC line.  Generally, black will be used for Hot, white will be used
for Neutral, and green or uninsulated wire will be used for Safety Ground.
While this is part of the NEC (Code) for electrical wiring (in the U.S.), it
is not always followed inside appliances.  You may also find brown for Hot,
blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances
and electronic equipment.

Where a non-polarized plug (cordset) is used, either AC wire can be Hot and
both wires will typically (but not always) be the same color.

Other colors may be used for switched Hot (e.g., red), thermostat control,
motor start, solenoid 1, etc.  Various combinations of colored stripes may
be used as well.  Unfortunately, in some cases, you will find that all the
wiring is the same color and tracing the circuit becomes a pain in the

Where multiple wires need to go from point A to point B along the same path,
they will often be combined into a single cable which is bundled using nylon
or cloth tie-wraps or run inside a single large flexible plastic sheath.  For
electronic interconnects and low voltage control and signal wiring, molded
flat cables are common (like those for the cables to the diskette and hard
drives of your PC).  These are quite reliable and can be manufactured at low
cost by fully automatic machines.

The thickness of the insulation of a wire or cable is not a reliable indication
of its capacity or voltage rating.  A fat wire may actually have a very skinny
central conductor and vice-versa.  In some cases, the wire conductor size and
voltage rating will be printed on the insulation but this not that common.
If replacement is needed, this information will be essential.  However, the
ampacity (maximum current) can be determined from the size of the metal
conductor and for any of the line powered appliances discussed in this
document, wire with a 600 V rating should be more than adequate.

The type of insulation is critical in appliances that generate heat - including
table lamps and other lighting fixtures.  There is special high temperature
insulated wire (fixture wire) which should be used when replacement is needed.
For heating appliances like toasters, hair dryers, and deep friers, fiberglass
or high temperature silicone based rubber insulated wire or insulating sleeves
must be used should the original wiring need replacement.  An appliance repair
motor rebuilding shop would be the most likely source - common electronics
distributors may not carry this stuff (especially if you only need a couple

Connections between individual wires and between individual wires and other
components are most often made by crimp or screw terminals, welding, or
press-in contacts.  For cables, actual multipin and socket connectors may
be used.

Common problems: internal wiring conductors broken, corroded, or deteriorated
due to heat or moisture.  Dirty, corroded, weakened, or damaged connector
contacts are common requiring cleaning and reseating or replacement.  Damage
to insulation from vibration, heat, movement, or even improper manufacture or
design is also possible.  Careless reassembly during a previous repair could
result in pinched broken wires or insulation as well as short circuits between
wires, or wiring and sharp sheet metal parts.

Testing: Inspect for obvious breaks or wires that have pulled out of their
terminations.  Integrity of wiring can be determined with a continuity checker
or multimeter on a the low ohms scale.  Flexing and wiggling wires especially
at connections while observing the meter will identify intermittents.

  6.7) Switches - power, mode, or speed selection

Most appliances have at least one switch to turn the appliance on and off.
In some cases, this may be combined with a thermostat or other control.
However, switches serve a variety of functions as well.

* Power - Nearly all appliances that run on AC directly (no wall transformer)
  provide some means of completely disconnecting at least one side of the AC
  line when not in use.  This may be a rocker, slide, push-push, trigger,
  toggle, rotary, or other separate switch.  It may also be combined with
  another function like a speed control or thermostat.

* Selector, mode, function - these switches may be used to determine speed
  in a mixer or blender, or the heat or air-only setting on a blow-dryer,
  for example.

* Internal (not user accessible) - these perform functions like detecting
  the position of a mechanism (e.g., limit switch), cam operated timing,
  and other similar operations that are not directly performed by the user.

In all cases, the function of a switch is the same - to physically make (on)
or break (off) the circuit or connect one signal to another.

* The most common type of switches have a set of metallic contacts (special
  materials to resist arcing and corrosion) which are brought together as a
  result of mechanical motion of a rocker, lever, etc. to complete the circuit
  There is usually some sort of snap action to assure rapid make and break of
  the circuit to minimize deterioration due to arcing.

* Mercury switches - found in thermostats, silent wall switches, and a variety
  of other places, use a small quantity of mercury (a metal which is a liquid
  at room temperature) to complete the circuit.  Depending on the orientation
  of a glass or metal/insulator capsule, the mercury either contacts a set
  of terminals (on) or is separate from them (off).  Since any arcing occurs
  in the liquid mercury, there is virtually no deterioration of internal parts
  of a mercury switch.  Life is nearly infinite when used within its ratings.
  See the section: "About mercury wall switches".

Common problems with switches include: dirt, worn, or melted contacts, broken
plastic or fiber parts, bad connections to terminals.

Testing: Switches can always be tested with a continuity checker or a
multimeter on a low ohms scale.

WARNING: Mercury is a heavy metal and is poisonous.  I know it is fun to play
with beads and globs of the stuff (and I have done it) but do not recommend
it.  Dispose of any from broken mercury switches or thermometers safely.  If
you insist on keeping it, use a piece of paper as a scoop and put the mercury
in a bottle with a tightly sealed cap.

  6.8) About mercury wall switches

The types of mercury switches used for wall switches are quite clever and
provide in effect a snap action (called hysteresis) due to their construction
and the surface tension of the liquid mercury itself.  This despite the fact
that the motion of the toggle lever is totally smooth and silent.  It is not
possible to put the lever in such a position that there could be marginal
contact and random on-off cycles.  The mercury capsule inside such a switch
consists of a metallic shell with an insulating (glass or ceramic) spacer in
between the two halves.  Connection to the switch's wiring is made via sliding
contacts to the metal portion of the capsule.  There is a small hole toward
one side in the spacer.  Rotating the capsule results in the mercury flowing
through the hole to make contact:

* In the off position, the hole is above the level of the liquid mercury.

* In the on position, the hole is below the level of the liquid mercury.

* When turning the switch on, the hole is rotated below the surface and as
  soon as the mercury touches, surface tension quickly pulls it together.
  There is no 'contact bounce'.

* When turning the switch off, the mercury pulls apart as the capsule is
  rotated to raise the hole.  Eventually, surface tension is not sufficient to
  hold the two globs of mercury together and they part suddenly.

Problems are rare with these mercury switches.  In fact, GE mercury switches
used to carry a *50* year warranty!  I don't know if they still do.

In principle, these are also the safest type of switch since any sparking or
arcing takes place inside the sealed mercury capsule.  However, the contact
between the screw terminals and the capsule are via sliding contacts (the
capsule is press fit between the metal strips to which the screws are attached)
and with time, these can become dirty, worn, or loose.  For this reason, some
electricians do not like mercury switches, particularly for high current

  6.9) Relays - electrically activated switches for power or control

Relays are switches that are activated by an electrical signal rather
than a button or toggle.  They are used to switch power (as in an central
air conditioning system) or control signals (as in a telephone or modem).

* The most common relays are electromechanical - an electromagnet is used
  to move a set of contacts like those in a regular switch.

* Solid state relays have no moving parts.  They use components like thyristors
  or transistors to do the switching.

For more information on relays, see the document: "Notes on the Troubleshooting
and Repair of Audio Equipment and other Miscellaneous Stuff".

  6.10) Contact configurations

The arrangement of contacts on a switch is often abbreviated mPnT where:

* 'm' identifies the number of separate sets of contacts.

* 'P' stands for Poles or separate sets of contacts.

* 'n' identifies the number of contact positions.

* 'T' stands for Throw which means the number of contact positions.

In addition, you may see:

* NC (Normally Closed and NO (Normally Open) may be used to designate terminals
  when the switch is in the off or deactivated state.  This applies to power
  switches where OFF would be down or released and ON would be up or pushed in.
  It also applies to momentary pushbutton switches and relays.

* MBB (Make Before Break) and BBM (Break Before Make) designate how the
  connections behave as the switch is thrown.  Most switches found in small
  appliances will be of the BBM variety.

This also applies to relays except that the contact switching is activated
by an electrical signal rather than a finger.

The most common types are:

* SPST - Single Pole Single Throw.  Terminal (A) is connected to terminal (B)
  when the switch is on:

        A ______/ _______ B

  This is the normal light or power switch.  For electrical (house) wiring,
  it may be called a '2-way' switch.

* DPST - Double Pole Single Throw.  Terminal (A) is connected to terminal (B)
  and terminal (C) is connected to terminal (D) when the switch is on:

        A ______/ _______ B
        C ______/ _______ D

  This is often used as a power switch where both wires of the AC line are
  switched instead of just the Hot wire.

* SPDT - Single Pole Double Throw.  A common terminal (C) is connected to
  either of two other terminals:

                 _______ NC
       C ______/
                 _______ NO

  This is the same configuration as what is known as a '3-way' switch for
  electrical (house) wiring.  Two of these are used to control a fixture
  from separate locations.
* DPDT - Double Pole Double Throw.  Essentially 2 SPDT switches operated by
  a single button, rocker, toggle, or lever:

                 _______ NC1
      C1 ______/
               : _______ NO1
               : _______ NC2
      C2 ______/
                 _______ NO2

* SP3T, SP4T, etc. - Single Pole selector switch.  A common terminal (C) is
  connected to one of n contacts depending on position.  An SP5T switch is
  shown below:
               _________ 1
                 _______ 2
       C ______/  ______ 3
                 _______ 4
               _________ 5

  6.11) Electrical overload protection devices - fuses and circuit breakers

The purpose of fuses and circuit breakers is to protect both the wiring
from heating and possible fire due to a short circuit or severe overload
and to prevent damage to the equipment due to excess current resulting
from a failed component or improper use (using a normal carpet vacuum
to clear a flooded basement).

Fuses use a fine wire or strip (called the element) made from a metal which
has enough resistance (more than for copper usually) to be heated by current
flow and which melts at a relatively low well defined temperature.  When the
rated current is exceeded, this element heats up enough to melt (or vaporize).
How quickly this happens depends on the extent of the overload and the type
of fuse.

Fuses found in consumer electronic equipment are usually cartridge type -
1-1/4" mm x 1/4" or 20 mm x 5 mm, pico(tm) fuses that look like green 1/4 W
resistors, or other miniature varieties.  Typical circuit board markings are
F or PR.

Circuit breakers may be thermal, magnetic, or a combination of the two.
Small (push button) circuit breakers for appliances are nearly always
thermal - metal heats up due to current flow and breaks the circuit
when its temperature exceeds a set value.  The mechanism is often the
bending action of a bimetal strip or disc - similar to the operation of
a thermostat.  Flip type circuit breakers are normally magnetic.  An
electromagnet pulls on a lever held from tripping by a calibrated spring.
These are not usually common in consumer equipment (but are used at the
electrical service panel).

At just over the rated current, it may take minutes to break the circuit.
At 10 times rated current, the fuse may blow or circuit breaker may open
in milliseconds.

The response time of a 'normal' or 'rapid action' fuse or circuit breaker
depends on the instantaneous value of the overcurrent.

A 'slow blow' or 'delayed action' fuse or circuit breaker allows instantaneous
overload (such as normal motor starting) but will interrupt the circuit
quickly for significant extended overloads or short circuits.  A large thermal
mass delays the temperature rise so that momentary overloads are ignored.  The
magnetic type breaker adds a viscous damping fluid to slow down the movement
of the tripping mechanism.

Common problems: fuses and circuit breakers occasionally fail for no reason
or simply blow or trip due to a temporary condition such as a power surge.
However, most of the time, there is usually some other fault with the
appliance which will require attention like a bad motor or shorted wire.

Testing: Fuses and circuit breakers can be tested for failure with a
continuity checker or multimeter on the low ohms scale.  A fuse that tests
open is blown and must be replaced (generally, once the circuit problem is
found and repaired.)  Of course, if the fuse element is visible, a blown
fuse is usually easy to identify without any test equipment.  A circuit
breaker that tests open or erratic after the reset button is pressed, will
need replacement as well.

  6.12) Fuse postmortem

Quite a bit can be inferred from the appearance of a blown fuse if the
inside is visible as is the case with a glass cartridge type.  One
advantage to the use of fuses is that this diagnostic information is
often available!

* A fuse which has an element that looks intact but tests open may have just
  become tired with age.  Even if the fuse does not blow, continuous cycling
  at currents approaching its rating or instantaneous overloads results in
  repeated heating and cooling of the fuse element.  It is quite common for
  the fuse to eventually fail when no actual fault is present.

* A fuse where the element is broken in a single or multiple locations blew
  due to an overload.  The current was probably more than twice the fuse's
  rating but not a dead short.

* A fuse with a blackened or silvered discoloration on the glass where the
  entire element is likely vaporized blew due to a short circuit.

This information can be of use in directly further troubleshooting.

  6.13) Fuse or circuit breaker replacement

As noted, sometimes a fuse will blow for no good reason.  Replace fuse,
end of story.  In this situation, or after the problem is found, what are
the rules of safe fuse replacement?  It is inconvenient, to say the least,
to have to wait a week until the proper fuse arrives or to tromp out to
Radio Shack in the middle of the night.

Even with circuit breakers, a short circuit may so damage the contacts or
totally melt the device that replacement will be needed.

Five major parameters characterizes a fuse or circuit breaker:

1. Current rating - this should not be exceeded (you have heard about not
   putting pennies in fuse boxes, right?)  (The one exception to this rule
   is if all other testing fails to reveal which component caused the fuse to
   blow in the first place.  Then, and only then, putting a larger fuse in
   or jumpering across the fuse  **just for testing** will allow the faulty
   component to identify itself by smoking or blowing its top!)  A smaller
   current rating can safely be used but depending on how close the original
   rating was to the actual current, this may blow immediately.

2. Voltage rating - this is the maximum safe working voltage of the circuit
   (including any inductive spikes) which the device will safety interrupt.
   Thus, you may see fuses where the elements look like [|------|] versus
   [|==--==|].  It is safe to use a replacement with an equal or high voltage

3. AC versus DC - fuses rated for AC and DC may not be the same.  For a given
   voltage, a shorter gap can be used to reliably interrupt an AC circuit
   since the voltage passes through zero 120 (100) times a second.  For
   example, a fuse rated 32 VDC may look similar to one rated for 125 VAC.

4. Type - normal, fast blow, slow blow, etc.  It is safe to substitute
   a fuse or circuit breaker with a faster response characteristic but
   there may be consistent or occasional failure mostly during power-on.
   The opposite should be avoided as it risks damage to the equipment
   as semiconductors tend to die quite quickly.

5. Mounting - it is usually quite easy to obtain an identical replacement.
   However, as long as the other specifications are met, soldering a normal
   1-1/4" (3AG) fuse across a 20 mm fuse is perfectly fine, for example.
   Sometimes, fuses are soldered directly into an appliance.

  6.14) Thermal protection devices - thermal fuses and thermal switches

These devices protect against excessive temperature due to either a fault
in the appliance (locked motor overheating), improper use (blow dryer air

There are three typical types:

1. Thermal fuses.  This is similar to an electrical fuse but is designed
   to break the circuit at a specific temperature.  These are often found
   in heating appliances like slow cookers or coffee percolators or buried
   under the outer covering of motor windings or transformers.  Some also
   have an electrical fuse rating as well.  Like electrical fuses, these
   are one-time only parts.  A replacement that meets both the thermal and
   electrical rating (if any) is required.

   CAUTION: When replacing a thermal fuse, DO NOT SOLDER it if at all
   possible.  If the device gets too hot, it may fail immediately or be
   weakened.  Crimp or screw connections are preferred.  If you must solder,
   use a good heat sink (e.g., wet paper towels, little C-clamps) on the leads
   between the thermal fuse and the soldering iron, and work quickly!

2. Thermal switches or thermal protectors (strip type).  These use a strip of
   bimetal similar to that used in a thermostat.  Changes in temperature
   cause the strip to bend and control a set of contacts - usually to
   to break a circuit if the set temperature is exceeded.  Commonly found
   in blow dryers and other heating appliances with a fixed selection of
   heat settings.  They may also be found as backup protection in addition
   to adjustable thermostats.

3. Thermal switches or thermal protectors (disk).  These use a disk of bimetal
   rather than a strip as in most thermostats.  The disk is formed slightly
   concave and pops to the opposite shape when a set temperature is exceeded.
   This activates a set of contacts to break (usually) a circuit if the rated
   temperature is exceeded.  They may also be found as backup protection in
   addition to adjustable thermostats.  A typical thermal switch is a small
   cylindrical device (i.e., 3/4" diameter) with a pair of terminals and a
   flange that is screwed to the surface whose temperature is to be monitored.

In some applications, device types (2) and (3) may be used as the primary
temperature regulating controls where adjustment is not needed.

  6.15) More on thermal fuses

(From: Paul Grohe (grohe@galaxy.nsc.com)).

The following is From Microtemps' literature (`95 EEM Vol.B p1388):

"The active trigger mechanism of the thermal cutoff (TCO) is an electrically
 non-conductive pellet. Under normal operating temperatures, the solid pellet
 holds spring loaded contacts closed. When a pre-determined temperature is
 reached, the pellet melts, allowing the barrel spring to relax. The trip
 spring then slides the contact away from the lead and the circuit is opened.
 Once TCO opens a circuit, the circuit will remain open until the TCO is

Be very careful in soldering these. If the leads are allowed to get too hot, it
may "weaken" the TCO, causing it to fail prematurely. Use a pair of needle-nose
pliers as heat sinks as you solder it.

I have replaced a few of these in halogen desk lamp transformers.  The
transformers showed no signs of overheat or overload. But once I got it
apart, the TCO's leads had large solder blobs on them, which indicated
that the ladies that assembled the transformers must have overheated the
cutouts leads when they soldered them.

The NTE replacement package also comes with little crimp-rings, for high-temp
environments where solder could melt or weaken (or to avoid the possibility
of soldering causing damage as described above --- sam).

  6.16) Controls 1 - adjustable thermostats and humidistats

Thermostats are use to regulate the temperature in heating or cooling type 
appliances.  Common uses include heaters, airconditioners, refrigerators,
freezers, hair dryers and blow dryers, toaster ovens and broilers, waffle
irons, etc.  These are distinguished from the thermal switches discussed
above in that they usually allow a variable temperature setting.

Four types are typically found in appliances.  The first three of these
are totally mechanically controlled:

1. Bimetal strip.  When two metals with different coefficients of thermal
   expansion are sandwiched together (possibly by explosive welding), the
   strip will tend to bend as the temperature changes.  For example, if the
   temperature rises, it will curve towards the side with the metal of lower
   coefficient of expansion.

   In a thermostat, the bimetal strip operates a set of contacts which make
   or break a circuit depending on temperature.  In some cases the strip's
   shape or an additional mechanism adds 'hysteresis' to the thermostat's
   characteristics (see the section: "What is hysteresis?").

2. Bimetal disk.  This is similar to (1) but the bimetal element is in the
   shape of a concave disk.  These are not common in adjustable thermostats
   but are the usual element in an overtemperature switch (see the section:
   "Thermal protection devices - thermal fuses and thermal switches").

3. Fluid operated bellows.  These are not that common in small appliances
   but often found in refrigerators, airconditioners, baseboard heaters,
   and so forth.  An expanding fluid (alcohol is common) operates a bellows
   which is coupled to a set of movable contacts.  As with (1) and (2) above,
   hysteresis may be provided by a spring mechanism.

Other variations on these basic themes are possible but (1)-(3) cover the
vast majority of common designs.

Testing of mechanical thermostats: examine for visible damage to the
contacts.  Use a continuity checker or ohmmeter to confirm reliable
operation as the knob or slider is moved from end to end if it will
switch at room temperature.  Gently press on the mechanism to get the
contacts to switch if this is not possible.  Use an oven on low or a
refrigerator or freezer if needed to confirm proper switching based
on temperature.

4. Electronic thermostats.  These typically use a temperature variable
   resistance (thermistor) driving some kind of amplifier or logic circuit
   which then controls a conventional or solid state relay or thyristor.
Testing of electronic thermostats:  This would require a schematic to
understand exactly what they are intended to do.  If a relay is used, then
the output contacts could perhaps be identified and tested.  However,
substitution is probably the best approach is one of these is suspected
of being defective.

Humidistats, as their name implies, are used to sense relative humidity
in humidifiers and dehumidifiers.  Their sensing material is something
that looks kind of like cellophane or the stuff that is used for sausage
casings.  It contracts and expands based on the moisture content of the
air around it.  These are somewhat fragile so if rotating the control
knob on a humidifier or dehumidifier does not result in the normal 'click',
this material may have been damaged or broken.

Testing of mechanical humidistats: examine for visible damage to the
contacts.  Use a continuity checker or ohmmeter to confirm reliable
operation as the knob or slider is moved from end to end.  Gently press
on the mechanism to get the contacts to switch if this is not possible.
Gently exhale across the sensing strip to confirm that the switching point

  6.17) What is hysteresis?

An intuitive explanation of hysteresis is that it is a property of a
system where the system wants to remain in the state that it is in -
it has memory.

Examples of systems with hysteresis:

* Thermostats - without hysteresis your heater would be constantly
  switching on and off as the temperature changed.  A working thermostat
  has a few degrees of hysteresis.  As the temperature gradually increases,
  at some point the thermostat switches off.  However, the temperature then
  needs to drop a few degrees for it to switch on again.

* Toggle switches - the click of a toggle switch provides hysteresis to
  assure that small vibrations, for example, will not accidentally flip
  the switch.

Examples of systems which ideally have little or no hysteresis:

* Audio amplifiers - input vs. output.

* Pendulums on frictionless bearings - force vs. position.

Hysteresis is usually added thermostats by the use of a spring mechanism
which causes the mechanism to want to be in either the open or closed
position but not in between.  Depending on the appliance, there may be
anywhere from 0 hysteresis (waffle iron) to 5-10 degrees F (space heater).
Sometimes, the thermal mass of the heated device or room provides the
hysteresis since any change to the temperature will not take place
instantaneously since the heating element is separated from the thermostat
by a mass of metal.  Therefore, some overshoot - which in effect performs the
same function as a hysteresis mechanism - will take place.

  6.18) Controls 2 - rheostats and potentiometers

These controls are usually operated by a knob or a slide adjustment and
consist of a stationary resistance element and a wiper that can be moved
to determine where on the fixed element it contacts.  In some cases, they
are not actually user controls but are for internal adjustments.  In other
cases, they are operated by the mechanism automatically and provide a means
of sensing position or controlling some aspect of the operation.

* Rheostats provide a resistance that can be varied.  Usually, the range is
  from 0 ohms to some maximum value like 250 ohms.  They are used to
  control things like speed and brightness just by varying the current
  directly, or via an electronic controller (see the section:
  "Electronic controllers - simple delay or microprocessor based").

                 B o-------------+
                 A o--------/\/\/\/\/\-----
                         250 ohm rheostat

  In the diagram above, the resistance changes smoothly from 0 to 250 ohms
  as the wiper moves from left to right.

  Very often, you will see the following wiring arrangement:

                 B o-------------+------+
                                 |      |
                                 V      |
                 A o--------/\/\/\/\/\--+
                        250 ohm rheostat

  Electrically, this is identical.  However, should the most common failure
  occur with the wiper breaking or becoming disconnected, the result will be
  maximum resistance rather than an open circuit.  Depending on the circuit,
  this may be preferred - or essential for safety reasons.

  Testing: Disconnect at least one of the terminals from the rest of the
  circuit and then measure with an ohmmeter on the appropriate scale. The
  resistance should change smoothly and consistently with no dead spots or

* Potentiometers are either operated by a knob or a slide adjustment and
  implement a variable resistance between two end terminals as shown below.
  This can be used to form a variable voltage divider.  A potentiometer (or
  'pot' for short) can be used like a rheostat by simply not connecting one
  end terminal.  These are most often used with electronic controllers.

                 B o-------------+
                 A o--------/\/\/\/\/\--------o C
                       1K ohm potentiometer

  In the diagram above, the resistance between A and B varies smoothly from
  0 to 1K ohms as the wiper moves from left to right.  At the same time, the
  resistance between B and C varies smoothly from 1K to 0 ohms.  For some
  applications, the change is non-linear - audio devices in particular so that
  the perceived effect is more uniform across the entire range.

  Testing: Disconnect at least two of the terminals from the rest of the
  circuit and then measure with an ohmmeter on the appropriate scale.
  The resistance should change smoothly and consistently with no dead
  spots or dips.  Try between each end and the wiper.  Check the resistance
  across the end terminals as well - it should be close to the stamped
  rating (if known).

Rheostats and potentiometers come in all sizes from miniature circuit board
mounted 'trimpots' to huge devices capable of handling high power loads.
The resistance element may be made of fine wire ('wirewound') or a carbon
composition material which is silkscreened or painted on.

  6.19) Interlocks - prevent operation with case or door open

Most of these are simple switches mechanically activated by the case or door.
Sometimes, optical or magnetic interlocks are used (rare on small appliances
but common on things like printers).  Line cords that are firmly attached to
the case and disconnect automatically when the case is removed are another
example of an interlock.  Interlocks may be designed to prevent injury during
normal operation (e.g.. food processor blades will not start when cover is
removed) or during servicing (remove AC power to internal circuits with case

1. Interlock switches.  Various kinds of small switches may be positioned
   in such a way that they disconnect power when a door is opened or cover
   is removed.  These may fail due to electrical problems like worn or
   dirty contacts or mechanical problems like a broken part used to activate
   the interlock.

   Testing: Use an ohmmeter or continuity checker on the switches.  The reading
   should either be 0 ohms or infinite ohms.  Anything in between or erratic
   behavior is indication of a bad switch or cord.

2. Attached cordset.  Should the case be opened, the cord goes with the case
   and therefore no power is present inside the appliance.  To get around
   this for servicing, a 'cheater cord' is needed or in many cases the
   original can be easily unfastened and used directly.

   Testing: Use an ohmmeter or continuity check to confirm that both wires
   of the cord are connected to both AC plug and appliance connector.  Wiggle
   the cord where it connects to the appliance and at the plug end as well to
   see if there might be broken wires inside.

  6.20) Light bulbs - incandescent and fluorescent

Small incandescent light bulbs are often used in appliances for interior
lighting or spot illumination.  The common 'appliance bulb' is simply
a 'ruggedized' 40 W incandescent light bulb in a clear glass envelope.
Other types are found in vacuum cleaners, microwave overs, makeup mirrors,
and so forth.

Testing: visual inspection will often reveal a burnt out incandescent light
bulb simply because the filament will be broken.  If this is not obvious,
use an ohmmeter - an infinite resistance means that the bulb is bad.

Small fluorescent lamps are often found in makeup mirrors, plant lights, and
battery powered lanterns.

Testing: The best test for a bad fluorescent bulb is to substitute a known
good one.  Unfortunately, there is no easy go-no go test for a fluorescent
lamp.  Other parts of the lamp or fixture (like the ballast or starter) could
also be bad.

See the sections on the appropriate lamp type for additional information.

  6.21) Indicators - incandescent or neon light bulbs or LEDs

Whereas lighting fixtures using incandescent or fluorescent bulbs are designed
to illuminate a room or small area, an indicator is simply there to let you
know that an appliance is on or in a specific mode.

There are three common types of electrical indicator lights:

1. Incandescent bulbs.  Just like their larger cousins, an incandescent
   indicator or pilot light has a filament that glows yellow or white hot
   when activated by a usually modest (1.5-28 V) source.  Flashlight
   bulbs are very similar but usually have some mechanical method of
   keeping the filament positioned reasonably accurately so that the
   light can be focussed by a reflector or lens.  Since the light spectrum
   of incandescent indicators is quite broad, filters can be used to obtain
   virtually any colored light.  Incandescent indicator lamps do burn out
   just like 100 W bulbs if run near their rated voltage.  However, driving
   these bulbs at reduced voltage can prolong their life almost indefinitely.

   Incandescent indicator lamps are often removable using a miniature screw,
   bayonet, or sliding type base.  Some are soldered in via wire leads.  Others
   look like cartridge fuses.

   Testing: Visual inspection will often reveal a burnt out incandescent light
   bulb simply because the filament will be broken.  If this is not obvious,
   use an ohmmeter - an infinite resistance is means that the bulb is bad.

2. Neon lamps.  These are very common as AC line power indicators because
   they are easy to operate directly from a high voltage requiring only a
   high value series resistor.

   They are nearly all the characteristic orange neon color although other
   colors are possible and there is a nice bright green variety with an
   internal phosphor coating that can actually provide some illumination
   as well.  While neon bulbs do not often burn out in the same sense as
   incandescent lamps, they do darken with age and may eventually cease to
   light reliably so flickering of old Neon bulbs is quite common.

   Some Neon bulbs come in a miniature bayonet base.  Most are soldered
   directly into the circuit via wire leads.

   Testing: Inspect for a blackened glass envelope.  Connect to AC line
   (careful - dangerous voltage) through a series 100K resistor.  If glow
   is weak or absent, Neon bulb is bad.

3. Light Emitting Diodes (LEDs).  LEDs come in a variety of colors - red,
   yellow, and green are very common; blue is just appearing.  These run
   on low voltage (1.7-3 V) and relatively low currents (1-20 mA).  Thus,
   they run cool and are easily controlled by low voltage logic circuits.
   LEDs have displaced incandescent lamps in virtually all electronic
   equipment indicators and many appliances.  Their lifetime easily exceeds
   that of any appliance so replacement is rarely needed.

   LEDs are almost always soldered directly into the circuit board since they
   rarely need replacement.

   Testing: Use a multimeter on the diode test scale.  An LED will have a
   forward voltage drop of between 1.7 and 3 V.  If 0 or open, the LED is
   bad.  However, note: some DMMs may not produce enough voltage on the diode
   test scale so the following is recommended:  Alternative: Use a 6 to 9 V DC
   supply in series with a 470 ohm resistor. LED should light if the supply's
   positive output is on the LED's anode.  If in doubt, try both ways,  If the
   LED does not light in either direction, it is bad.

  6.22) Heating elements - NiChrome coils or ribbon, Calrod, Quartz

All heating elements perform the same function: convert electricity into
heat.  In this they have one other characteristic in common: they are all
nearly 100% efficient.  The only electrical energy which does not result in
heat is the slight amount of light (usually red-orange) that is produced
by a hot element.

There are 3 basic types of heating elements.  Nearly every appliance on
the face of the planet will use one of these:

1. NiChrome coil or ribbon.  NiChrome is an alloy of Nickel and Chromium
   which has several nice properties for use in heating appliances - First,
   it has a modest resistance and is thus perfect for use in resistance
   heating elements.  It is easily worked, is ductile, and is easily formed
   into coils of any shape and size.  NiChrome has a relatively high melting
   point and will pretty much retain its original shape and most importantly,
   it does not oxidize or deteriorate in air at temperatures up through the
   orange-yellow heat range.

   NiChrome coils are used in many appliances including toasters, convection
   heaters, blow-dryers, waffle irons and clothes dryers.

   The main disadvantage for our purposes is that it is usually not possible
   to solder this material due to the heating nature of its application.
   Therefore, mechanical - crimp or screw must be used to join NiChrome
   wire or ribbon to another wire or terminal.  The technique used in the
   original construction is may be spot welding which is quick and reliable
   but generally beyond our capabilities.

   Testing: Visual inspection should reveal any broken coil or ribbon.  If
   inspection is difficult, use a multimeter on the low ohms scale.  Check
   for both shorts to the metal chassis as well as an open element (infinite

2. Calrod(tm) enclosed element.  This encloses a fine coiled NiChrome wires
   in a ceramic filler-binder inside a tough metal overcoat in the form of a
   shaped rod with thick wire leads or screw or plug-in terminals.

   These are found in toaster oven/broilers, hot plates, coffee makers,
   crock pots and slow cookers, electric range surface elements, conventional
   and convection ovens and broilers.

   Testing: When these fail, it is often spectacular as there is a good
   chance that the internal NiChrome element will short to the outer casing,
   short out, and melt.  If there is no visible damage but the element does
   not work, a quick check with an ohmmeter should reveal an open element or
   one that is shorted to the outer casing.

3. Quarts incandescent tube.  These are essentially tubular high power
   incandescent lamps, usually made with a quartz envelope and thus their

   These are found in various kinds of radiant heaters.  By running a less
   than maximum power - more orange heat - the peak radiation is in the
   infra-red rather than visible range.

   Testing: Look for a broken filament.  Test with an ohmmeter just like
   an incandescent light bulb.

  6.23) Repair of broken heating elements

In appliances like waffle irons and toaster ovens, these are usually welded.
This is necessary to withstand the high temperatures and it is cheap and
reliable as well.  Welding is not normally an option for the doit yourselfer.  
However, if you are somewhat suicidal, see the section: "Improvised welding
repair of heating elements" for a more drastic approach.

I have used nuts and bolts, say 6-32, bolt, wire, washer, wire, washer,
lockwasher, nut.  Depending on how close to the actual really hot element
it is, this may work.  If you are connecting to the coiled element, leave
a straight section near the joint - it won't get as hot.

The use of high temperature solder or brazing might also work.

The best approach is probably to use high temperature crimp connectors:

(The following from: sad@garcia.efn.org (Stephen Dunbar))

You can connect heating element wires with high-temperature solderless
connectors that are crimped onto the wires. Be sure to get the special
high-temp connectors; the ordinary kind will rapidly oxidize and fall apart at
high temperatures. If you want to join two wires to each other, you'll need
either a butt splice connector (joins the wires end-to-end) or a parallel
splice connector (the wires go into the connector side-by-side). To fasten
a wire to a screw terminal you can use a ring or spade connector (though
as noted above, a screw, nut, and washer(s) should work fine --- sam). If your
waffle iron has quick disconnect terminals you'll need the opposite gender
disconnect (AKA Faston). These come in both .187" and .250" widths. 

Your best bet for getting these connectors in small quantity is probably a
local appliance parts outlet that caters to do-it-yourselfers. If you can't
find what you need there, try Newark Electronics (branches all over the
place). I have an old copy of their catalog which lists SPC Technology
Voltrex Brand High Temperature Barrel Terminals in several styles: ring,
spade, disconnect, and butt splice. The prices were around $10 to $12 per
100 (this catalog is a couple of years old) for wires in the 22-18 or
16-14AWG size ranges, almost twice that for the heftier wire gauges. (Be
sure to determine the wire gauge of your heating elements so you can get the
right size terminal.) 

You can spend a *lot* of money on crimp tools, but for occasional light use
you can probably get by with one of those $10 gadgets that crimp, strip &
cut wires, and cut bolts--the sort of thing you'd find in your local home
center or Radio Shack.

(From: Nigel Cook (diverse@tcp.co.uk)).

The thin stainless steel strip found spot welded to multicell NiCd batteries
make good crimps for joining breaks in heater resistance wire.  Form a small
length of this strip around a needle or something similar to make a tight
spiral with enough clearance to go over doubled-up heater wire.  Abraid or
file the cut ends of the broken wire.  Crimp into place with a double lever
action crimper.  If there is an area of brittle heating element around the
break then cut out and splice in a replacement section with two such crimps.
Such a repair to my hot-air paint stripper (indispensable tool in my
electronics tool-kit) has survived at least 50 hours.

(From: Dan Sternberg (steberg@erols.com)).

Another old trick for nichrome repair is to make a paste of Borax, twist the
two broken end together, and energize the circuit.  A form of bond welding
takes place.  I've have used this on electric clothes dryer heater elements
with good luck.

  6.24) Solenoids - small and large

Solenoids are actuators operated by electromagnets that are used to operate
valves, slide or engage various parts, eject or prevent opening of a door,
and other functions.  While shapes and sizes may vary, all electrically
operated solenoids use an electromagnet - AC or DC - to pull on a movable
piece called an armature which generally moves back and forth but rotary
motion is also possible.

Solenoids are usually two position devices - they are not used to provide
intermediate amounts of force or travel like motors.

Sizes ranges from small 1/2" long units providing a fraction of an ounce of
force and 1/8" travel to large 3" long units providing many pounds of force
with travels of 2" or more.

Testing: Inspect for free movement.  Use an ohmmeter to confirm that the
coil is intact.  There could be other problems like shorted turns in the
coil but these would be less common than lack of lubrication or an open
coil.  Check voltage on operating solenoid to determine whether drive power
is present.

  6.25) Small electronic components - resistors, capacitors, diodes

A variety of small electronic components may be found in appliances though
unlike true electronic equipment, these do not usually run the show.

Resistors - may be used in various ways to adjust the current flowing in
part of a circuit.  Many different types of resistors are possible - tiny
carbon or metal film types looking like small cylindrical objects often
with colored bands which indicate the value.

Power resistors - larger cylindrical or rectangular often ceramic coated.
These may get quite hot during operation.  Their resistance value and power
rating are usually printed on the resistor.

Capacitors - a variety of shapes and sizes.  Some may look like disks,
jelly beans, cylinders, boxes, etc.  Their value is often marked in uF or pF.

Diodes or rectifiers - solid state devices that permit electric current
to only flow in one direction (positive current in the direction of the
arrow when marked this way).  These are most often used in appliances to
change AC to DC or to cut the power to a motor or heater (by allowing only
half of the AC current to pass).

For more information on these types of components, see any good introductory
electronics text.

  6.26) Motors - universal, induction, DC, timing

A large part of the functionality of modern appliances is based on the
use of motors of one form or another.  We devote an entire chapter to
motors.  The following is just an introduction.

Motors come in all shapes and sizes but most found in small appliances
can be classified into 5 groups:

        1. Universal motors.
        2. Single phase induction motors
        3. Shaded pole induction motors.
        4. Small permanent magnet DC motors.
        5. DC brushless motors.
        6. Synchronous timing motors.

See the chapter: "Motors 101" for more detailed information on the common
types of motors found in small appliances.

  6.27) Fans and Blowers - bladed or centrifugal

The entire purpose of a particular appliance may be to move air or this
may simply be needed for cooling.  Obviously, portable and window fans
are an example of the former.  However, many appliances have built in fans
you may not even be aware of as part of the motor(s) or other rotating

There are two primary types of configurations:

1. Bladed fans - we are all familiar with the common desk or window fan.
   This uses a set of rotating blades - typically 3-5 to gather and direct
   air.  In the specific case of an oscillating desk fan, a gear drive
   linked to the motor also permits the general direction of air movement
   to be controlled in a back-and-forth motion.  I recently saw one where
   in addition to moving back and forth, the front grille can be set to
   rotate at an adjustable rate providing more variation in air flow.

   The direction of the air movement with respect to blade rotation is
   determined by the pitch - the tilt - of the blades.  Although reversing
   air direction is possible by reversing the motor, one direction is usually
   more effective than the other due to the curve of the blades.

2. Centrifugal blowers.  These use a structure that looks similar to a
   squirrel cage to suck air from the center and direct it out a plenum
   formed around the blower.  While these may be found in all sizes, the
   most common household application is in the vacuum cleaner.  Large
   versions of these blowers are used in central heating and airconditioning
   systems, window airconditioners, and oil burners.

   Direction of rotation of the blower motor does not change the direction
   of airflow.  However, one direction will be more effective than the
   other (where the blower is rotating in the same direction as the way exit
   port on the air plenum points.  Because of this, it is not possible for a
   vacuum cleaner to blow out the suction hose due to a reversed motor (which
   in itself is for all intents and purposes, impossible as well).  This is
   usually caused by back flow due to a blockage.

  6.28) Bearings and bushings

The shafts of rotating parts normally are mounted in such a way that friction
is minimized - to the extent needed for the application.  A bearing is any such
joint with more specific terms used to describe the typical types found in
small appliances - or lawnmower, automobile engines, or 100 MW turbines.

Plain bearings - these consist of an outer sleeve called a bushing in which
a polished shaft rotates.  The bushing may be made of a metal like brass or
bronze or a plastic material like Teflon(tm).  The shaft is usually made of
steel though other materials may be found depending on the particular needs.
Where a metal bushing is used, there must be means provided for lubrication.
This may take the form of oiling grooves or holes and an oil reservoir (usually
a saturated wad of felt) or the bushing itself may be sintered.   Metal
particles are compressed at high temperature and pressure resulting in a
very porous but strong material which retains the lubricating oil.

Under normal conditions, a plain bearing wears only during start and stop
cycles.  While the shaft is rotating at any reasonable speed, there is no
metal to metal contact and thus no wear.  With a properly designed and
maintained bearing of this type, a very thin oil film entirely supports
the shaft - thus the importance of clean oil.  Your automobile engine's
crankshaft is entirely supported by these types of bearings.

Eventually, even 'lubricated for life' bearings of this type may need to be
disassembled, cleaned, and lubricated.  The plain bearings in small appliances
must be lubricated using a proper light oil like electric motor or machine
oil - not automotive engine oil and NEVER NEVER WD40.

NEVER, ever, use WD40 as a lubricant (unless specifically recommended by the
manufacturer of the equipment, that is)!  WD40 is not a good lubricant despite
the claims on the label.  Legend has it that the WD actually is an abbreviation
for Water Displacer - which is one of the functions of WD40 when used to coat
tools.  WD40 is much too thin to do any good as a general lubricant and will
quickly collect dirt and dry up.  It is also quite flammable and a pretty good
solvent - there is no telling what will be affected by this.

WD40 has its uses but lubrication unless specifically recommended by the
manufacturer (of the equipment, that is) is not one of them.  Results initially
may be good with that instant gratification that comes from something returning
to life.  However, the lighter fractions of WD40 evaporate in a few days 

For very small metal-in-plastic types, the following might be useful:

(From: Frank MacLachlan (fpm@bach.n2.net)).

"I've had good luck with a spray lubricant called SuperLube.  It contains a
 solvent which evaporates and leaves a Teflon film which doesn't migrate
 or retain dust.  I spray some into a spray paint cap and then apply the
 solution with a toothpick, allowing the lubricant to wick into the bearing
 areas.  Worked great for some balky Logitech mice I purchased at a local
 swap meet."

Frictionless bearings are usually of the ball or roller variety.  An inner
ring called a race rotates supported by a series of balls or rollers inside
an outer race.  There is virtually no friction even at stand-still with these
bearings.  However, rolling metal to metal contact is maintained at all speeds
so they are not quite as wear free as a properly maintained and constantly
rotating plain bearing.  However, for all practical purposes in small
appliances, these will last a long time and are rarely a problem.

Sometimes, reworking an appliance to use a ball bearing instead of a plain
bearing is a worthwhile effort - I have done this with electric drills and
shop vacs.  They run smoother and quieter with ball bearings.  Not
surprisingly, higher-end models of these devices (which use ball bearings)
share parts with the cheaper versions and finding standard ball bearings
that would fit was not difficult.

  6.29) Mechanical controllers - timing motors and cam switches

While these are not that common on small appliances, they may be present
in washing machines, dryers, dishwashers. and refrigerator defrost timers.
They in themselves may be considered small appliances - and often can be
repaired or replaced easily.

Most of these are just small timing motors (synchronous motors running
off of the AC line) which rotate one or more cams (disks with bumps) which
activated one or more switches at appropriate times during the rotation
cycle.  Typical cycle times range from a minute or less to several hours
(refrigerator defrost timer).  Most like washing machine timers are in
the 1 hour range.  Sometimes, the motor is stopped during certain portions
of the cycle awaiting completion of some other operation (i.e., fill).

These controllers therefore consist of several parts:

* Timing motor.  A very small synchronous AC line operated motor with
  an integral gear train is most common.  Sometimes, the rotor and
  geartrain are in a sealed, easily replaceable unit - a little metal
  case that clamps within the pole pieces of the AC field magnet.  In
  other cases, it is a separate motor assembly or an integral part of
  the overall timer mechanism.

* Escapement (not present on all types).  This is a device which converts
  the continuous rotation of the timing motor to a rapid movement for each
  incremental cam position.  A common type is a movement every 45 seconds
  to the next position.  This assures that the make or break action of the
  switches is rapid minimizing arcing.

* Cam(s).  One or more cams made of fiber composite, plastic, or metal,
  are rotated on a common shaft.  There will be one set of switch contacts
  for each circuit that needs to be controlled.

* Switches.  These will either be exposed sets of contacts or enclosed
  'microswitches' which are operated by the cams.

Testing: If the controller is not working at all, check for power to the
motor. Listen for the sound of the motor parts rotating.  Check for gummed
up lubrication or broken parts.

If some of the circuits do not work, check the switches for dirty or worn
contacts or broken parts.

  6.30) Electronic controllers - simple delay or microprocessor based

These can range from a simple R-C (resistance-capacitance) circuit to
provide the time delay in a toaster to sophisticated microprocessor based
systems for programming of a coffee maker or microwave oven.

While generally quite reliable, bad solder connections are always a
possibility as well as failed parts due to operation in an environment
prone to temperature extremes.

Testing: Check for bad solder connections and connectors that need to
be cleaned and reseated.  Inspect for obviously broken or burned parts.
Test components for proper value.

For digital clock/programmers or  microprocessor based controllers, not
much else can be done without a schematic - which not likely to be easily

  6.31) Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-acid

More and more small appliances and power tools are cutting their
cords and going to battery power.  Although there are a large number
of battery types, the most common for power applications (as opposed
to hearing aids, for example) are:

* Alkaline - primary (non-rechargeable, for the most part), long shelf life,
  high energy density.

* Lithium - primary and secondary (rechargeable) available though most
  appliance applications (which are just beginning to develop) are not
  rechargeable.  Long shelf life, very high energy density.  Still quite

* Nickel Cadmium - most common rechargeable technology in cordless appliances
  and power tools.  However, relatively fast self discharge and on about
  half the capacity of a similar sized Alkaline.

* Lead-Acid - secondary type similar to the battery in your automobile
  but packaged in a totally sealed container which is virtually indestructible
  and leakproof.  Medium self discharge rate but will deteriorate if left
  discharged for an extended period of time.

See the chapter: "Batteries" for more information.

  6.32) AC adapters and chargers - wall 'warts' with AC or DC outputs

These wall adapters are used to power many small electronic devices and
appliances directly and/or to recharge their batteries.  They usually
plug directly into the wall socket and convert the 115 VAC (U.S.) to a
lower voltage - 3 V to 24 V AC or DC typical.  More sophisticated units
may actually be a switching power supply with smart electronic control of
battery charging and power management.   The following are typical types:

* AC output - 3 to 24 VAC (or more) at 50 mA to 3 A.  The only internal
  component is a power transformer which may include a thermal or ordinary
  fuse for protection.

* DC output - 3 to 24 VDC (or more, under load) at 50 mA to 1.5 A.  In
  addition to the power transformer, there is a rectifier, filter capacitor,
  and possibly a three terminal IC regulator (not that common).  Some type
  of protection will probably be built in as well.

* Universal/switching power supply - typically 6 to 18 VDC at .5 to 3 A.
  These will usually operate off of any voltage input from 90 to 240 VAC
  (or DC) and provide a well regulator output.  There will generally be 
  an internal fuse as well as overvoltage and overcurrent protection.

In some cases, a single adapter will put out multiple voltages.  See the
chapter: "AC Adapters and Transformers" for more information.

Chapter 7) AC Line and Battery Powered Household Appliances

  7.1) Table lamps

This is the most popular type of lighting for reading or general illumination.
The type described in this section takes normal 115 VAC light bulbs.

The common table lamp is just a light duty cordset, switch, and sockets
for one or more incandescent light bulbs.  In many cases, the switch and
socket are combined into one assembly.  In other designs, particularly
where more than one bulb can be lit independently (for example, a large
bulb up top and a night light in the base), a separate switch (rotary or
push-push) selects the light bulb(s) to be turned on.

For the most common combined switch and socket, there are several varieties
and these are all generally interchangeable.  Therefore, if you want to take
advantage of the added convenience of a 3-way bulb allowing low, medium, and
high illumination, it is a simple matter to replace the simple on-off
switch in your lamp with a 3-way switch (not to be confused with the 3-way
switches used in house wiring to control a single light fixture from 2 places).

Push-push, pull chain, and rotary switches are common for simple on-off
control.  The 3-way switches are usually of the rotary variety with
off-low-medium-high selected as the knob is rotated.  The 3-way bulb has
two filaments which can be switched on individually or in combination to
provide the 3 levels of illumination.

Dimmer sockets can often be substituted for the normal kind as long as
conventional incandescent bulbs (and not compact fluorescents) are to
be used.

Touch and even sound activated switch-sockets are also available though
my personal recommendation is to stay away from them.

Most common problems: burned out bulb, worn switch, bad plug or cord.
Where the light flickers, particularly if jiggling or tapping on the
switch has an effect, a bad switch is almost always the problem.  Switch
failure is more common when using high wattage bulbs but can occur just
due to normal wear and tear.

Replacements for most common switches and sockets are readily available at
large hardware stores, home centers, and electrical supply houses.  It is
best to take along the old switch so that an exact match (if desired) can
be obtained.  While the thread sizes for the screw on socket shells are
quite standard, some older lamps may have an unusual size.  For more
complicated switches with multiple sockets, label or otherwise record the
wiring.  If color coded, cut the wires so that the colors are retained
at both the lamp and switch ends.

  7.2) Rebuilding a basic table lamp

As noted in the Introduction, virtually any table lamp can be restored
to like-new electrical condition for a few dollars at most.  The following
is the detailed procedure for the majority of common table lamps found
in the U.S.

This is assumed to be the type of lamp which has a combination socket and
switch with a metal (brass-colored usually) outer shell.  It is your decision 
as to whether a simple on-off switch or a 3-way type is to be used - they are
usually interchangeable and a normal light bulb can be put into a 3-way socket
(two clicks of the knob will be needed to switch a normal light bulb on or off,
however).  You can also put a 3-way bulb into a normal socket but you will, of
course, only get one level of illumination (medium).  For lamps with lighted
bases, also see the section: "Lamps with night-light bulbs in their base".

You will need: (1) a new socket/switch of the appropriate type and (2) a
new cordset (if you want to replace this as well).  A polarized type plug
is desirable to minimize the possibility of shock when changing bulbs.  A
medium size straight blade screwdriver and wire strippers are the only
required tools.

First, remove and set aside any shade, frosted chimney, and other cosmetic

Unplug the lamp!!!

Examining the metal shell, you will note that it is in two pieces.  If you
look carefully, there will probably be indications of where firmly pressing
the top portion will allow it to be separated from the bottom part mounted
on the lamp.  These are usually near where the knob, button, or chain, enters
the switch.  Sometimes, a fine screwdriver blade will be useful to gently
pry the two halves apart.

With the top part removed, unscrew and disconnect two wires and remove
the switch.  If desired, loosen the set screw (if any) and unscrew the
bottom portion of the shell.  If you are simply replacing the switch, at
this point you would just attach the new one and reassemble in reverse
order.  Screw on the bottom of the new switch enough so that it is either
tight or until the threads are fully engaged but not pressing on or protruding
above the cardboard insulating disk in the bottom half of the shell.  If
the entire assembly is still loose, it should be possible to tighten hardware
on the bottom of the lamp to secure it against rotation.  Note: it is
important to do this to avoid eventual damage to the wires should the switch
move around significantly during normal use.

To replace the cordset, you may need to partially remove any felt pad
that may be glued to the base of the lamp.  Sometimes, it is possible to
cut off the old plug, attach the new cord to the end of these wires, and
pull it through.  However, in most cases, there will be a knot or other
strain relief in the original cord which will make this impossible (and
you will want to replicate this in the replacement as well).  Therefore,
if needed, carefully peel back the felt pad only enough to gain access to
the interior.  In some cases, just cutting a small X in the center will
allow sufficient access and this can be easily patched with a piece of
cloth tape.

Install the new cord in exactly the same way as the original with a knot
for a strain relief if needed.  If there was no strain relief to begin
with, adding a knot is a good idea if there is space for one in the base.
Snake the cord through to the top of the lamp.

Strip the ends of the wires to a length of about 1/2 inch and twist the
strands tightly together in a clockwise direction.  If you are using a
cordset with a polarized plug, identify the wire attached to the wide
prong (with a continuity checker or ohmmeter if it is not clearly marked
by a stripe on the insulation) and connect it to the silver colored screw.
Connect the wire attached to the narrow prong to the brass colored screw.
Always wrap in a clockwise direction.  See the section: "Attaching wires
to screw terminals".

Confirm that there are no loose wire strands and that the insulation is
nearly flush with the screw to avoid possible shorts.  Pop the shell top
with its insulating cardboard sleeve over the switch and press firmly onto
the base.  There should be a very distinct click as it locks in place.

If needed, adjust the strain relief at the base of the lamp so that pulling
on the cord does not apply any tension to the wires attached to the switch.
Tighten the nut in the base of the lamp holding the entire assembly in place
if the socket is still loose and rotates easily.  Don't overdo it - the
supporting structure is often just a glass jar or something similar.  Put
a drop of Loctite, nail polish, Duco cement, or something similar - or a
second nut - on the threads to prevent the nut from loosening.  Use some
household cement to reattach the felt pad you peeled back earlier.

  7.3) Lamps with night-light bulbs in their base

These are the types of lamps where either the normal bulb on top or a smaller
one in the base (or both) can be turned on using a turn-key or pull-chain.

This is a standard, if somewhat unusual socket.  It is basically the same
as a 3-way type but with the extra connection going to the bulb in the base
of the lamp.  In the old days when sockets were assembled with screws instead
of rivets, it might have been possible to modify a new 3-way socket to provide
the extra connection.

An electrical supply parts distributor or lamp store should have what you need
or be able to order it for you.

Take note of the connections as you remove the old socket to avoid mistakes.
When routing the wires to the bulb in the base, avoid allowing the hot bulb
from contacting the insulation - the plastic stuff might melt (for a 7 W or
less wattage bulb and high temperature insulation is probably not an issue,

  7.4) High intensity lamps

These include several types but they all use a transformer to reduce the
115 VAC to something lower like 12-24 V.

Tensor(tm) (and their clones) high intensity lamps have been around for
over 30 years and are essentially unchanged today.  They use a low voltage
transformer producing 12-24 VAC along with a special high output light bulb
that looks similar to an automotive tail light.  However, it uses substantially
more current for the same voltage and puts out a much more intense, whiter
light.  These are not halogen lamps though their spectral characteristics are
similar since the filaments run hotter than normal incandescents - and have
shorter lives.

Some will have multiple levels of illumination based on selecting taps on
the transformer.  Normal dimmers may not work (and should not be used) with
these due to their transformer design - damage to the dimmer or lamp may
result and this may be a fire hazard.

Problems with Tensor lamps tend to center around the socket and switch.
These may fail due to overheating as a result of the high temperature and
high current operation.  Replacements are available but they may take some
effort to locate.  A replacement lamp may be cheaper.  (I often find complete
Tensor lamps in perfect operating condition at garage sales for around $2.

  7.5) Halogen lamps and fixtures

Halogen lamps share many of the design characteristics of high intensity
lamps in that they are designed for local high intensity lighting and use a
transformer usually (though some may use solid state voltage conversion
instead).  While some halogen lamps come with dimmers, some of the advantages
of the halogen cycle are lost if the bulbs are not run at full power.  The
worst case is where they are operated just below full power - too cool for
the halogen cycle to take place but hot enough for substantial filament
evaporation to occur.

Should the dimmer portion of such a fixture fail or become unreliable, it may
a blessing in disguise since the lamp will either run at full intensity or can
be easily rewired to do so by bypassing the electronics and just using the
on/off switch!

WARNING: halogen bulbs run extremely hot and are a serious fire hazard and
burn hazard if not properly enclosed.  When changing a halogen bulb, wait
ample time for the old one to cool or use an insulated non-flammable glove
or pad to remove it.  When installing the new bulb, make sure power is off,
and do not touch it with your fingers - use a clean cloth or fresh paper
towel.  If you do accidentally touch it, clean with alcohol.  Otherwise,
finger oils may etch the quartz and result in early - possibly explosive
failure - due to weakening of the quartz envelope.

  7.6) Safety guidelines for use of halogen lamps

These guidelines were prompted by a number of fires including some fatalities
that have been linked to improper use of halogen lamps - in particular the
high power torchiere variety of floor lamps.  However, the guidelines apply
to many other types of halogen lamps including work-lights, desk lamps, slide
and overhead projectors, and other lamps or fixtures where the bulb is not
entirely enclosed and thermally insulated from the exterior.

(Source: The Associate Press except as noted).

Safety groups recommend the following precautions for owners of halogen
torchere lamps with tubular bulbs:

* Place the lamps where they cannot be tipped over by children, pets, or
  strong drafts (away from open windows, for example).

* Never use halogen lamps in children's bedrooms or playrooms where combustible
  objects like stuffed toys may be accidentally placed on top of or next to

* Never use a replacement bulb of a higher wattage or of a different type
  than specified by the manufacturer.  Avoid bulbs larger than 300 W.

* Never attempt to replace or discard a bulb that is too hot to touch.

  Do not touch the new bulb with your fingers as the oils and acids may make
  them more prone to exploding.  Clean the bulb thoroughly with isopropyl
  alcohol after any accidental contact (--- sam).

* Never drape cloth over the lamp.

* Operate the lamps at less than maximum wattage on a dimmer whenever possible.

  Note that this may not result in maximum life but will be safer due to the
  lower temperature of the bulb (--- sam).

* Keep lamps away from elevated beds like bunk beds where the bedding may get
  too close to the bulb.

* Never use unprotected halogen lamps in locations like bathrooms where water
  may splash resulting in the bulb exploding (--- sam).

* Never operate lamps with their thermal or UV shields removed (--- sam).

  7.7) What causes a lamp to flicker?

Many things can cause the light bulb in a table lamp to flicker:

* Loose bulb(s) :-).

* Bad switch.  These do wear out particularly if multiple high wattage bulbs
  are being used.  If gently jiggling the switch results in flickering this
  is the most likely cause.

* Bad connections.  These could be anywhere but the most likely locations
  (where only a single lamp is involved) would be either at the screw
  terminals on the switch or from a plug that isn't making secure contact in
  the outlet - check it.

* Voltage fluctuations.  Occasional flickering when high wattage appliances
  kick in is not unusual especially if they are on the same branch circuit but
  could also be a symptom of other electrical problems like a loose Neutral
  connection - see the section: "Bad Neutral connections and flickering lights
or worse".

  If a dimmer control is present, keep in mind that these are somewhat more
  sensitive to slight voltage fluctuations especially when set at low levels.
  You may simply not have noticed any flickering with a normal on/off switch.

  7.8) Touch lamp problems

Personally, I think touch lamps are one of the dumber uses of technology
to appear on this planet but that is just my opinion :-).

These are susceptible to damage from voltage surges or just plain old random
failures.  In addition, the current surge that often results at the instant
an incandescent bulb burns out (the bright flash) may blow the thyristor in
the electronics module.

If the lamp is stuck on, the thyristor is probably shorted.  The specific
part can be replaced but to be sure it is bad, some testing will be needed
and it is probably soldered in place.  However, if you have repaired an
ordinary lamp, you will be able to replace the entire module fairly easily.

If the lamp is stuck off, there could be a bad connection or bad bulb, or
the electronics module is defective.  Again, replacement is straightforward.

Erratic problems could be due to bad connections, dried up electrolytic
capacitors (especially if the electronics module is near the hot bulb), or
even external E/M interference (e.g., a dimmer or vacuum cleaner on the same

Some problems are of the following type:

"I have 2 touch lamps in the bed room and they are both plugged in to the
 same receptacle.  Every once in a while the lamps come on by themselves
 for no apparent reason.  Even more strange is that every so often just
 one lamp turns on by itself."

(From: Tim Moore (tmoore@interserf.net)).

These use a MOSFET type circuit to switch the lamps on and off. The circuit
is attached to the metal in the lamp base. When you touch it the impedance
changes ever so minutely but enough to change the MOSFET from off to on
and visa versa. My wife could never get our lamps to switch, she often
had to blow on her hand first to get it moist so it would make better
contact. Here is part of the problem. It takes a certain amount of
signal from the lamp base to switch the circuit. Electronic parts all
have acceptable ranges of operation and when put into identical circuits
they sometimes perform differently. One circuit might need a good hard
touch while the other might need only a slight touch. Power surges would
often switch one of my lamps, although it didn't happen often. A strong
radio signal could do it too. The bottom line is that these lamps are
not rocket science and can't be counted on as 100% reliable. Sorry,
that's the truth. You give up a little to get the convenience of just
having to touch them. I ended up removing mine - an electrical storm
wiped one out and wiped the other out a few years later. 

  7.9) Touch lamps and RF interference

While many people swear by touch lamps, nearly as many swear at them since in
addition to frequent failures (bulb burn-outs killing the triac, for example),
they can also be tempermental, cycling through their brightness settings
and/or turning on or off due to static electricity, power line transients
causing RFI, and stray pickup from the local ham rig.

(Portions from: John Evans - N0HJ (jaevans@codenet.net)).

Here is a fix my buddy, Ed, a fellow ham radio operator, has come up
with to solve this problem.

As usual it took 8 months and 10 minutes to fix.

Two parts: 1/4 watt, 1k Ohm resistor and 2.5 mH 1/2 watt size molded coil.
Connect in-line with the touch wire.

I send 2 or more watts from my rig.  My son works the CB.

You'll find it on when you get home.

So the darn thing is an oscillator which changes frequency when you touch it.
The circuit does the rest.  By adding the resistor/inductor pair, its
sensitivity is reduced and the problem disappears.

One more thing:  (Most important!), you won't hear interference FROM the
oscillator in the lamp anymore on your radio.

And don't open up the module inside the lamp base, you are wasting your time
there, and adding more work to glue the module back together.

Just Choke off the sense wire with the resistor and 2.5 mH choke.  You'll be

  7.10) Incandescent fixtures

A fixture is normally permanently mounted to a wall or ceiling.  However,
aside from not usually having a plug - being directly wired - they are
similar to table lamps in what is inside.

There will be one or more sockets for light bulbs - often all wired in
parallel so that all the bulbs come on at the same time.  For wall fixtures,
there may be a switch on the fixture though most often the switch is mounted
on the wall elsewhere.

Unlike table lamps where most of the heat rises from the bulb away from the
socket, mounting the sockets horizontally or inverted (base up) can result
in substantial heating and eventual deterioration of the socket and wiring.
Common problems relate to this type of problem - bad connections or brittle
wire insulation.  Replacement parts are generally available at home centers
and electrical supply houses.  Just make sure to kill power before working
on any fixture wired into your house's electrical system!

  7.11) Removing the base of a broken light bulb

Turn off power and double check!  Wear safety goggles to protect against
flying bits of glass.

Then use a pair of needlenose pliers or any other tool that will grip what
is left of the base to twist it free.  A piece of a raw potato may even work!

  7.12) Locating burnt out bulbs in series circuits

Christmas and other decorative lights are constructed as series strings
of low voltage light bulbs as shown below:

    Male o------O----O----O----O----O----O----O----O---+
    Plug                                               |

Or the following which permits several strings to be connected end-to-end:

            |             Bulbs                           |
    Male o--+---O----O----O----O----O----O----O----O---+  +--o Female
    Plug                                               |       Socket

Many variations on these are possible including multiple interleaved series
strings.  One of the bulbs in each circuit may be a flasher.  All newer light
sets must include a fuse as well.

In a series connected circuit, if one bulb burns out, all lights go out.  The
newer types include a device in each bulb which is supposed to mechanically
short out that bulb if it burns out.  However, these don't always work or you
may have a set that doesn't have this feature.

The following assumes a single series circuit - large light sets (e.g.,
perhaps 50 or more) will have multiple series strings so you will have
to identify the particular circuit that is bad.  If more than one bulb
is burnt out, this may further complicate matters.
To locate a burnt out bulb in a series string, you can use the binary search
approach: pull a bulb in the middle of the string.  Test the bulb and between
the power cord end and the middle for low resistance.  If these are ok, you
know the bad bulb is in the other half.  Then divide the 'bad' portion in half
and test one half of it and so forth.  For example, using this technique, you
will need to make at most 6 sets of measurements to locate a bad bulb in a 50
light set.

Sears, K-Mart, Radio Shack, among others sell inexpensive testers (e.g.,
Lite-Tester Plus, about $4).  These detect the electric field generated by
the (now floating) wire on the Hot side of the gap of the burnt out filament.
These will also locate open wires and blown fuses in the same manner.

I have also heard of bulb sets in which the individual bulbs are gas filled
in such a way that if the filament breaks, current flows across the gap
through the gas resulting in a faint glow in the burnt out bulb.  I don't
know if these things still exist.

WARNING: Do not be tempted to bypass a bad bulb with a wire.  This will reduce
the total resistance and increase the current to the remaining lamps shortening
their life.  Do this a few times, and the entire string will pop.  This is a
serious safety hazard especially on older light sets that may not have internal
fuses.  Some fuses look like lamps - replace only with an identical fuse - not
with a lamp!

  7.13) Comments on Christmas tree bulb/string repair

Original type of problem: No light but fuses are good and no obvious damage.

(From: Ken Bouchard (bouchard@ime.net)).

My advice, is trash them and go out and buy new ones.  After all, you can get
them typically around 5-10 bucks a set.

Then you have the old set to raid bulbs from, for the ones that blow out.

Quality control is not an issue when they build xmas lights.  One slight tug
of a wire, can break it, and the entire set goes dead.

First I assume you wiggled all the bulbs, often just a loose bulb causes this.
In the smaller type bulb sets the string is wired in sections, so one bulb
goes out, and every 4th or 5th one is dead.

The little bulbs were also designed, that if the filament breaks in the bulb
a piece of foil inside it shorts out that bulb so that the remaining lights
keep on working. This works up to a point, until more than 4-5 bulbs blow
out at once, then the remaining ones get too much voltage and blow out too.

Often the cheesy sockets get water in them and corrode, and/or the wires on
the bulb get twisted or broken.

They also use a cheap method of crimping the wiring together in these lights.
Most times you can find the broken wire, by inspecting, seeing where it goes
into the socket it pulls out easily.

Well avoid doing this when the set is live (heh...) unless you like the idea
of getting zapped.

  7.14) Controlling a fixture or outlet from multiple locations

Although the specific case of controlling a fixture or outlet from exactly
two locations is a special case of switches at more than 2 locations, each
is described separately since the former is much more common.

Should you care, these implement the multiple input XOR (exclusive OR) logic
function for controlling electrical devices.

Note: See the section: "Dimmer switches and light dimmers" if you would like
to have control of brightness of a lamp or fixture from multiple locations.

* For exactly two locations (say at the bottom and top of basement stairs), you
  will need a pair of what are known as 3-way switches.

  These are actually SPDT (Single Pole Double Throw) switches which look like
  ordinary wall switches but have 3 screws instead of 2.  Two of these screws
  will be the same color (usually brass) while the third will be different
  (darker copper or brown).  They may be marked as well.

  Note that a socket for a 3-way bulb for a lamp is not related to this - only
  the name is similar.

  Typical wiring for controlling a fixture or outlet from exactly two locations
  is as follows:

            Location 1         Location 2
             3-way SW     A     3-way SW          +---------+
                /o----------------o\              | Fixture |
    Hot o-----/                      \o-----------|   or    |--------o Neutral
                 o----------------o        Center | Outlet  | Shell
                          B               (brass) +---------+ (silver)

                                           /o---o                   o---o
  A 3-way switch connects either up  o---/         or down  o---o\        .
                                            o---o                  \o---o

  As usual, the brass screw on the fixture or outlet should be connected to
  the Hot side of the wiring and the silver screw to the Neutral side.

  Another common variation is shown below:

                                          Location 1           Location 2
                                           3-way SW    Rd :     3-way SW
                                    : Bk      /o------------------o\ 
        Hot o-------------------------------/          Wh :          \o---+
                                    :          o------------------o       |
                    +---------+     :                     :               |
                    | Fixture |     : Wh   Splice      Bk :               |
    Neutral o-------|   or    |---------------X---------------------------+
                    | Outlet  |     :     (Wirenut)       :
                    +---------+   14-2                  14-3

  Details may differ for your particular installation (like to which sides the
  Hot and Neutral are connected and/or particular wire colors used).

* For more than two locations (say at 3 doors to your dining room), you will
  need a combination of 3-way switches and 4-way switches.  Two of the 3-way
  type will be needed at the ends of the circuit (below) with 1 or more 4-way
  type in between.  Thus for 'n' switch locations, n-2 of the 4-way switches
  will be needed.

  4-way switches have 4 terminals arranged as two pairs.  In one position pair
  1 is connected to pair 2 straight through.  In the other position, the
  connections are interchanged.

  Typical wiring for controlling a fixture or outlet from 3 or more locations
  is as follows:

        Location 1     Location 2     Location 3
         3-way SW   A   4-way SW   A   3-way SW        +---------+
            /o------------o\ /o-----------o\           | Fixture |
  Hot o---/                 /               \o---------|   or    |---o Neutral
             o------------o/ \o-----------o    Center  | Outlet  | Shell
                    B              B           (brass) +---------+ (silver)

                                           o---o              o\ /o
  A 4-way switch connects either straight         or exchange   /   .
                                           o---o              o/ \o

  This can be extended to an arbitrary number of positions.

  As usual, the brass screw on the fixture or outlet should be connected to
  the Hot side of the wiring and the silver screw to the Neutral side.

  Note that a 4-way switch can be constructed from a DPDT (Double Pole Double
  Throw) type (e.g., toggle switch) as follows:

                    |              |
      A(in) o---------------+      |
                    |       |      |
                    +----o  o/ o-------+------o A(out)
                             :     |   |
                    +----o  o/ o---+----------o B(out)
                    |       |  DPDT    |
      B(in) o---------------+  toggle  |
                    |          switch  |

  For low voltage (non-house wiring) or panel mount applications, this may be
  easier than using actual 4-way switches (which are probably not available in
  small sizes).

The 3-way switches (at least the basic white, ivory, or brown toggle type)
can be found nearly anyplace that sells common electrical devices including
hardware stores and home centers.  You may have to look a little harder for
4-way switches as well as styles or colors to match your decor as these are
not as widely available.  However, a decent electrical supply house should
have all of these.

The wires marked A and B (sometimes called 'travelers') may be in a single
(Romex) cable and should be on the screws that are both the same color.

If you do use Romex with a black and white wire, put black tape on the
insulation at the ends of the white wire (or paint the ends black) to
indicate that this is a Hot wire and not a Neutral.  This is required by
Code but allows the use of this type of wire.

These diagrams represent one wiring arrangement.  Sometimes, there are other
slight variations.  For example, you might find the switches in the Neutral
instead of Hot portion of the wiring - however, this is not recommended.

  7.15) Identifying unmarked wiring for 3-way switch

(Also see the section: "Controlling a fixture or outlet from multiple locations".)

So you forgot to label the wires before you removed the old switch, huh? :-).

You have several options:

* It may be obvious from the way the box is wired as to which are the
  A/B pair.

* Use a tester to figure out which wire is which (see below).

* Interchange the different colored screw wire with one of the others.
  If this doesn't fix it, interchange the different colored screw wire
  with the other one.  As long as you have only touched the wires on the
  old switch, you cannot damage anything by doing this.

* Get an electrician.

Of course, kill power before touching or changing anything!

Here is one way to identify the proper wires more quickly than trial and error:

1. Identify the Hot wire.  With all 3 wires in each box disconnected and their
   ends exposed, use a tester between each one and the a earth ground (the
   box if metal and properly grounded).  With power on, only one of the 6
   wires will be live.

Now, turn off the power and confirm that it is off by retesting the hot wire
you identified above.

2. Connect the lone screw (the different or darker colored one) on one switch
   to this Hot wire.  Connect the same-color screws on the switch to the other
   two wires.  This should take care of one box.

3. With any luck, you should be able to connect the wires in the other
   box exactly the same way color wise.

(From: CodeElectric@Worldnet.att.net).

Check both boxes.  There will be a single Hot - that goes on the common of
the 3-way switch.  Put the other two wires on the other two screws.

Now, at the other switch, you will find one hot.  Put that on a screw, not
the common.  Switch the other switch, and you'll find another hot.  That is
the other traveler.  You've got one wire left,,, that's the other common.

In more detail:

First, shut off the power to the circuit.  Then remove the wires from the
switches.  Ignore the colors of the wires... there's too many combinations to
use so the colors won't mean anything.

Look closely at the switches.  You will find one screw different from the
other two.  It may be black, while the other 2 are gold, or may have the word
'common' printed near it.  This is, (duh!) the 'common' terminal.  The other
two are 'traveler' terminals.  Having identified the commons and travelers,
make sure your family knows you're working with live wires, and let them know
not to touch!!!!

Turn the power back on, and out of the six wires that came off of the two
switches, ONE of them will have power.        Once you find that one, turn the
power back off, and hook that one wire to the common terminal of a switch. 
Hook the other two wires in that box to the traveler terminals.  It doesn't
matter which one goes where.  Put the switch into the box, and place the
cover back on.        You're done with than switch.

Now turn the power back on, and check the remaining three wires.  One will be
hot.  Flip the first switch, and another will be hot.  These are your traveler
wires.  Turn the power back off, and hook those two wires to the two traveler
terminals on the second switch.  Again, it makes no difference which goes
where.  The final wire goes to the common terminal.  Button everything up, and
you should be done.

Turn the power back on, and you should be up and running.

  7.16) Dimmer switches and light dimmers

In the old days, a dimmer was a large high wattage rheostat put in series
with the light bulb.  These were both inefficient and producers of a lot
of heat.  Modern dimmers use a device called a triac (a type of thyristor)
which is a solid state switch to control illumination by turning the light
bulb on for only a part of each AC half-cycle (100 or 120 times a second
depending on where you live) as determined by the adjustment knob or slider.
Once switched on, it remains on for the remainder of the half-cycle:

* For low intensity, the current is switched on late in the half-cycle.

* For medium intensity, the current is switched on around the middle of the

* For high intensity, the current is switched on early in the half-cycle.

* For full intensity, the triac may be bypassed entirely.  There will probably
  be a detectable click position with the control set to full brightness if
  this is present.

Dimmers are available to replace standard wall switches and even for
use in place of the light bulb socket/switch in most table lamps.
However, nearly all of these are designed only for normal incandescent
light bulbs - not fluorescents, compact fluorescents, or high intensity
or halogen lamps (or any other type of lamp with a transformer).

(There are special dimmers for use with fluorescent lamps but these must
be specifically matched to the lamp type and wattage and their dimming
range is usually not very wide.  See: the fluorescent lamp information at
http://www.misty.com/~don/light.html for a discussion of dimming
techniques and details on several relatively simple approaches that may work
for your needs.)

Installation is generally very straightforward as there are only two wires
and polarity does not matter.  They simply replace the existing switch.

To assure long life, it is best to select a dimmer with a higher power rating
than your maximum load.  For example, if you are using four 100 W bulbs, a
600 W dimmer should be the minimum choice and one rated at 1000 W would be
better.  This is particularly true if halogen bulbs are used since these may
be harder on dimmers than normal types.  Further derating should be applied
where multiple dimmers are installed in the same outlet box resulting in
greater combined heating.  Higher wattage dimmer switches will have better
heat sinking as well which should result in the active components - the
thyristors - running cooler.  Dimmers are under the most stress and generate
the most heat when operating at about 50% output.

Dimmers may fail due to power surges, excess load, momentary fault (short)
at the instant of light bulb failure, or just plain old age.  A failed dimmer
will generally be stuck at full brightness since the thyristor will have
shorted out.  The mechanical on-off switch which is part of the dimmer
will probably still work.

* A power surge may result in a failed dimmer just like any other solid
  state device.

* Make sure you are nor overloading the circuit controlled by the dimmer.  Most
  common types are rated for 600 W maximum with heavy duty types up to 1200 W
  or more.  My advice is to not load them to more than 60-75% of their rating.

* When light bulbs burn out, there can be an instantaneous spike of high
  current due to the failure mechanism.  This may blow a fuse or trip a
  circuit breaker - but it may also blow out a dimmer control.

* Dimmers are not always of the highest quality design or construction and
  parts may run hot - ever touch the wall plate of a dimmer running at 50%
  power?  Long term reliability may not be that great.

It is not generally worth worrying about repair of a dimmer as they are so
inexpensive.  However, before replacement confirm that there is no actual
problem with the wiring (like a short circuit in the fixture) and that you
are not overloading the dimmer.

  7.17) Typical dimmer schematics

These are the type of common light dimmers (e.g., replacements for standard
wall switches) widely available at hardware stores and home centers.

While designed for incandescent or heating loads only, these will generally
work to some extent with universal motors as well as fluorescent lamps down
to about 30 to 50 percent brightness.  Long term reliability is unknown for
these non-supported applications.

CAUTION: Note that a dimmer should not be wired to control an outlet since it
would be possible to plug a device into the outlet which might be incompatible
with the dimmer resulting in a safety or fire hazard.

  7.18) Simplest dimmer schematic

The first schematic is of a normal (2-way) inexpensive dimmer - in fact this
contains just about the minimal number of components to work at all!

S1 is part of the control assembly which includes R1.

The rheostat, R1, varies the amount of resistance in the RC trigger circuit.
The enables the firing angle of the triac to be adjusted throughout nearly
the entire length of each half cycle of the power line AC waveform.  When
fired early in the cycle, the light is bright; when fired late in the cycle,
the light is dimmed.  Due to some unavoidable (at least for these cheap
dimmers) interaction between the load and the line, there is some hysteresis
with respect to the dimmest setting: It will be necessary to turn up the
control a little beyond the point where it turns fully off to get the light
to come back on again.

          Black o--------------------------------+--------+
                                                 |        |
                                              |  |        |
                                           R1 \  |        |
                                        185 K /<-+        |
                                              \  v CW     |
                                              |         __|__ TH1
                                              |         _\/\_ Q2008LT
                                              +---|>|   / |   600 V
                                              |   |<|--'  |
                                          C1 _|_  Diac    |
                                       .1 uF --- (part of |
                       S1                     |    TH1)   |
          Black o------/ ---------------------+-----------+

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/R1).

  7.19) 3-way dimmer schematics

There are at least two varieties of inexpensive 3-way style dimmer switches
which differ mainly in the switch configuration, not the dimmer circuitry.
You will probably have no reliable way of telling them apart without testing
or disassembly.

None of the simple 3-way dimmer controls permit totally independent dimming
from multiple locations.  With some, a dimmer can be installed at only one
switch location.  Fully electronic approaches (e.g., 'X10') using master
programmers and addressable slave modules can be used to control the intensity
of light fixtures or switch appliances on or off from anywhere in the house.
See the section: "True (electronic) 3-way (or more) dimmers".

However, for one simple, if inelegant, approach to independent dimming, see
the section: "Independent dimming from
two locations - kludge #3251".

  7.20) Simple 3-way dimmer schematic 1

The schematic below is of one that is essentially a normal 3-way switch with
the dimmer in series with the common wire.  Only one of these should be
installed in a 3-way circuit.  The other switch should be a normal 3-way
type.  Otherwise, the setting of the dimmer at one location will always
affect the behavior of the other one (only when the remote dimmer is at its
highest setting - full on - will the local dimmer have a full range and

Note that the primary difference between this 3-way dimmer schematic and
the normal dimmer schematic shown above is the addition of an SPDT switch -
which is exactly what is in a regular 3-way wall switch.  However, this
dimmer also includes a choke (L1) and capacitor (C2) to suppress Radio
Frequency Interference (RFI).  Operation is otherwise identical to that
of the simpler circuit.

This type of 3-way dimmer can be used at only one end of a multiple switch
circuit.  All the other switches should be conventional 3-way or 4-way types.
Thus, control of brightness is possible only from one location.  See the
section: "True (electronic) 3-way (or more) dimmers" for reasons for thistrue
restriction and for more flexible approaches.

   Red 1 o--------o
                 S1   o----+------------+-----------+
                           |            |           |
   Red 2 o--------o        |         R1 \  ^ CW     |
                           |      220 K /<-+        |
                           |            \  |        |
                           |            |  |        |
                           |            +--+        |
                           |            |           |
                           |         R2 /           |
                       C2 _|_      47 K \           |
                  .047 uF ---           /         __|__ TH1
                           |            |         _\/\_ SC141B
                           |            +---|>|   / |   200 V
                           |            |   |<|--'  |
                           |        C1 _|_   D1     |
                           |   .062 uF ---  Diac    |
                           |            |           |
   Black o-----------------+---CCCCCC---+-----------+
                         40 T #18, 2 layers
                       1/4" x 1" ferrite core 

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/R1).

  7.21) Simple 3-way dimmer schematic 2

The schematic below is of a 3-way dimmer with a slightly more complex
switching arrangement such that when the local dimmer is set to full on or
full off, it is bypassed.  (If you ignore the intermediate dimming range of
the control, it behaves just like a normal 3-way switch.)  With this scheme,
it is possible to have dimmers at both locations without the dimmer
circuitry ever being in series and resulting in peculiar behavior.

Whether this is really useful or not is another story.  The wiring would be
as follows:

              Location 1             Location 2
             3-way Dimmer      A    3-way Dimmer     +---------+
                  /o----------------------o\         |  Lamp   |
    Hot o------o/    Silver 1     Silver 2   \o------|   or    |-----o Neutral
           Brass   o----------------------o   Brass  | Fixture |
                     Silver 2  B  Silver 1           +---------+

(If dimming interacts, interchange the A and B wires to the silver screws at
one dimmer).

This one uses a toggle style potentiometer where the up and down positions
operate the switches.  Therefore, it has 3 states: Brass to Silver 1 (fully
up), dim between Brass and Silver 1 (intermediate positions), and Brass to
Silver 2 (fully down).

                        Br  /o---o            Br   o---o          Br/\/o---o
  3-way dimmer is up o---o/   S1   or down o---o\  S1    or Dim o---o  S1
                             o---o                \o---o               o---o
                              S2                   S2                  S2

However, it is still not possible to have totally independent control - local
behavior differs based on the setting of the remote dimmer (details left as
an exercise for the reader).

Like the previous circuit, this dimmer also includes a choke (L1) and
capacitor (C3) to suppress Radio Frequency Interference (RFI).  It is just
a coincidence (or a matter of cost) that the 3-way dimmers have RFI filters
and the 2-way type shown above does not.

  Silver 1 o---+----------------+--------------------+-----------+
               |                |                    |           |
               |                |                 R1 \  ^ Up     |
               |                |              150 K /<-+        |
               |                |                    \  |        |
               |                |                    |  |        |
               |                |          +---------+--+        |
               |                |          |         |           |
               |            C3 _|_         |      R2 /           |
               |               ---         |    22 K \           |
               |                |          |         /         __|__ TH1
               |                |      C2 _|_        |         _\/\_ 
               |                | .047 uF ---        +---|>|   / |   200 V
           Up \                 |          |         |   |<|--'  |
               |                |          |     C1 _|_   D1     |
               |                |          |.047 uF ---  Diac    |
               |                |          |         |           |
               |  Dim  o--------+---CCCC---+---------+-----------+
               |     /               L1
     Brass o---+---o               12T #18
                           1/4" x 1/2" ferrite core
                 Down  o         
  Silver 2 o-----------+

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/S2/R1).

  7.22) True (electronic) 3-way (or more) dimmers

The objective is to be able to control a single fixture from multiple locations
with the capability of dimming as well as just power on/off.

The simple type of 3-way dimmers are just a normal dimmer with a 3-way instead
of normal switch.  This allows dimming control from only one location.  The
other switches in the circuit must be conventional 3-way or 4-way type.

Connecting conventional dimmers in series - which is what such a hookup would
require - will not really work properly.  Only if one of the dimmers is set
for full brightness, will the other provide full range control.  Anywhere in
between will result in strange behavior.  The other dimmer may have a very
limited range or it may even result in oscillations - periodic or chaotic
variations in brightness.  The safety and reliability of such an arrangement
is also questionable.

True 3 way dimmers do exist but use a more sophisticated implementation
than just a normal dimmer and 3-way switch since this will not work with
electronic control of lamp brightness.  One approach is to have encoder knobs
(similar to those in a PC mouse) or up/down buttons at each location which
send pulses and direction info back to a central controller.  All actions
are then relative to the current brightness.  A low cost microcontroller or
custom IC could easily interface to a number, say up to 8 (a nice round
number) - of control positions.  The manufacturing costs of such a system
are quite low but due to its specialty nature, expect that your cost will
be substantially higher than for an equivalent non-dimmable installation.

If control of intensity at only one of the locations is acceptable, a
regular dimmer can be put in series with the common of one of the normal
3-way switches.  However, your brightness will be set by that dimmer alone.
See the section: "Typical dimmer schematics".

An alternative is to use X-10 technology to implement this sort of 
capability.  This would likely be more expensive than a dedicated
multi-way switch control but is more flexible as well.  X-10 transmits
control information over the AC lines to select and adjust multiple
addressable devices like lamps and appliances.

However, for the adventurous, see the section: "Independent dimming from
two locations - kludge #3251".

  7.23) Independent dimming from two locations - kludge #3251

Here is a scheme which will permit dimming with independent control from two
locations.  Each location will have a normal switch and a dimmer knob.  The
toggle essentially selects local or remote but like normal 3-way switches, the
actual position depends on the corresponding setting of the other switch:

                 Location 1       Location 2
           +--------+  4-way SW    3-way SW
Hot o--+---| Dimmer |----o\ /o--------o\            +---------+
       |   +--------+      /            \o----------| Fixture |------o Neutral
       |              +--o/ \o--------o      Center +---------+ Shell
       |              |                      (brass)           (silver)
       |              |            +--------+
       |              +------------| Dimmer |--+
       |                           +--------+  |

As usual, the brass screw on the fixture or outlet should be connected to the
Hot side of the wiring and the silver screw to the Neutral side.

The dimmers can be any normal knob or slide type with an off position.

Note that as drawn, you need 4 wires between switch/dimmer locations.
4-way switches are basically interchange devices - the connections
are either an X as shown or straight across.  While not as common as
3-way switches, they are available in your favorite decorator colors.

If using Romex type cable in between the two locations, make sure to tape or
paint the ends of the white wires black to indicate that they may be Hot as
required by Code.

And, yes, such a scheme will meet Code if constructed using proper wiring

No, I will not extend this to more than 2 locations!

Also see the section: "Controlling a fixture or outlet from multiple locations".

CAUTION: However, note that a dimmer should not be wired to control an
outlet since it would be possible to plug a device into the outlet which
might be incompatible with the dimmer resulting in a safety or fire hazard.

  7.24) How do touch dimmers work?

(From: Neil).

Touch dimmers work in a couple of different ways, depending on the IC used.
Simple ones, such as those in the cheap 'touch lamps' that you find for sale
on market stalls, etc. normally have three or four preset brightness levels
and an OFF setting, which are operated sequentially: touch once for full
brightness, again to dim slightly, again to dim a bit more, etc, until the OFF
setting is reached. The next touch will then bring the lamp to full

The better (and more expensive) units, such as the touch dimmer switches that
are sold as direct replacements for conventional light switches, are similar,
but have many more steps. A single touch will usually bring the lamp to full
brightness, while keeping your finger in contact with the touch plate will
slowly dim the lamp. You just remove your finger when the lamp is at the
required brightness level.

Both kinds of touch dimmer have three basic parts;

1. A touch sensor - this normally works by picking up mains hum from the
   touch plate, and rectifying it in a high-gain amplifier.

2. A ramp generator - normally in the form of a digital counter with DAC

3. A mains power control element - Generally a thyristor or triac. In some
   designs, this is encapsulated within the IC, while in others it is a
   discrete component.

Most touch dimmers can be operated by standard push-button switches as well as
a touch plate, and many can be adapted for remote control.

There are a number of specially designed IC's available for touch dimmers,
notably the HT7704B ,a four-step device for touch lamps as described above,
and the SLB0586A, which is the other kind, with facilities for remote control.

  7.25) Light dimmers and interference with radio or TV

Due to the sharp edges on the power supplied by a cheap light dimmer, Radio
Frequency Interference (RFI) may be conducted back down the wiring directly to
other appliances and/or radiated through space as well.  Effects will include
noise bars in the picture on some TV channels and/or a buzz in the audio
across portions of the AM radio band.

Better light dimmers will include a bypass capacitor (e.g., .01 uF, 1KV)
and a series inductor to suppress RFI but these components were often left
off in basic models.  The FCC has tightened up on their regulations around
1992 so replacing older dimmer switches with newer ones may be the easiest

Installing in-line power line filters may work but other options like
replacing all your house wiring with metal conduit, or only listening to FM
radio are probably not realistic!

  7.26) Can I use a dimmer to control transformer operated low voltage lighting?

It is very tempting to try using a common light dimmer to control devices
using power transformers.  Will this work?

There really is no definitive answer.  It is generally not recommended
but that doesn't mean it won't work perfectly safely in many instances.

However, in principle this may be dependent on what is on the secondary
side - a transformer appears more inductive when it is lightly loaded - and
on the design of your particular dimmer.

It could blow the dimmer or result in the dimmer simply getting stuck at
full power for some or all of the control range since the inductive load
will cause the current to continue flowing even after the voltage has gone
to zero and the thyristor should shut off.  If it works reliably in your
situations, then this is not a problem.  Again, it may be load dependent.

It probably will result in more audible noise from the transformer but this
is probably harmless except to your sanity.

The only safety issues I can think of and these relate to the transformer
running hotter than normal as a result of core saturation.  This might
happen at certain settings if the thyristor is not switching at the same
point on the positive and negative half cycles.  There would be a net DC
current flow through the transformer which is not good,  If the thyristor
were to fail in such a way that it only triggered on one half cycle, very
large DC current could flow.  However, a suitably rated fuse or circuit
breaker and thermal cutout should handle both these situations.

Note: If your dimmer uses an SCR instead of a triac, this will result in
immediate and catastrophic failure. An SCR results in a DC output.  However,
full range dimmers usually use triacs.

The bottom line: I cannot provide any guarantees.

  7.27) Flashlights and lanterns

Battery operated flashlights (torches for those on the other side of the Lake)
and lanterns are among the simplest of appliances.  We probably all have a box
or drawer full of dead flashlights.

The most common problem after dead batteries is very often damage due to
leaky batteries.  Even supposedly leak-proof batteries can leak.  Batteries
also tend to be prone to leaking if they are weak or dead.  Therefore,
it is always a good idea to remove batteries from any device if it is not
to be used for a while.  How to assure the batteries will be with the
flashlight?  Put them in separate plastic bags closed and fastened with
a twist tie.

Test the batteries with a multimeter - fresh Alkalines should measure 1.5 V.
Any cell that measures less than about 1.2 V or so should be replaced as they
will let you down in the end.  On a battery tester, they should read well into
the green region.

Check the bulb with a multimeter on the ohms scale - a bad bulb will test
open.  Bulbs may fail from use just like any other incandescent lamp or
from a mechanical shock - particularly when lit and hot.  Replacement bulbs
must be exactly matched to the number and type of batteries (cells).  A
type number is usually stamped on the bulb itself.  There are special
halogen flashlight bulbs as well - I do not really know how much benefit
they provide.

The switches on cheap flashlights are, well, cheaply made and prone to
unreliable operation or total failure.  Sometimes, bending the moving
metal strip a bit so it makes better contact will help.

Clean the various contacts with fine sandpaper or a nail file.

If a flashlight has been damaged as a result of battery leakage, repair
may be virtually impossible.

High quality flashlights are another matter.  Maglights(tm) and similar
units with machined casings and proper switches should last a long time
but the same comments apply to batteries - store them separately to avoid
the possibility of damage from leakage.  Keep a spare bulb with each of
these - the specialty bulbs may be harder to find than those for common
garbage - sorry - flashlights.

Rechargeable flashlights include a NiCd or lead-acid battery (one or more
cells in series) and the recharging circuitry either as part of the unit
itself or as a plug-in wall adapter or charging stand.  See the sections:
"Battery chargers" and "Typical rechargeable flashlight schematics" for more

  7.28) Typical rechargeable flashlight schematics

Here are circuit diagrams from several inexpensive rechargeable flashlights.
These all use very 'low-tech' chargers so battery life may not be as long as
possible and energy is used at all times when plugged into an AC outlet.

  7.29) First Alert Series 50 rechargeable flashlight schematic

This one is typical of combined all-in-one units using a lead-acid battery
that extends a pair of prongs to directly plug into the wall socket for

It is a really simple, basic charger.  However, after first tracing out the
circuit, I figured only the engineers at First Alert knew what all the diodes
were for - or maybe not :-).  But after some reflection and rearrangement of
diodes, it all makes much more sense:  C1 limits the current from the AC line
to the bridge rectifier formed by D1 to D4.   The diode string, D5 to D8 (in
conjunction with D9) form a poor-man's zener to limit voltage across BT1 to
just over 2 V.

The Series 50 uses a sealed lead-acid battery that looks like a multi-cell
pack but probably is just a funny shaped single cell since its terminal voltage
is only 2 V.

Another model from First Alert, the Series 15 uses a very similar charging
circuit with a Gates Cyclon sealed lead-acid single cell battery, 2 V, 2.5
A-h, about the size of a normal Alkaline D-cell.

WARNING: Like many of these inexpensive rechargeable devices with built-in
charging circuitry, there is NO line isolation.  Therefore, all current
carrying parts of the circuit must be insulated from the user - don't go
opening up the case while it is plugged in!

                                             2V LB1  Light
                                           1.2A +--+ Bulb    S1
                                       +--------|/\|----------o/ o----+
            _ F1   R3         D3       |        +--+                  |
   AC o----- _----/\/\---+----|>|--+---|----------------------+       |
          Thermal  15    |    D2   |   |                 4A-h |       |
           Fuse          | +--|>|--+   |         BT1 - |+ 2V  |       |
                         | |  D4       +--------------||------|-------+
                         +----|<|--+   |               |      |       |
                           |  D1   |   |  D8   D7   D6   D5   |  D9   |
          |        |                                                  |
          |        /                                                  |
         _|_ C1    \ R1                                               |
         --- 2.2uf / 100K                                             |
          |  250V  \                                                  |
          |        |               R2          L1  LED                |
   AC o---+--------+--------------/\/\-----------|<|------------------+
                                 39K 1W       Charging

  7.30) Black & Decker Spotlighter Type 2 rechargeable flashlight

This uses a 3 cell (3.6 V) NiCd pack (about 1 A-h).  The charging circuit is
about as simple as it gets!

         11.2 VRMS                                +---------------o/ o----+
  AC o-----+ T1       R1      LED1         D1     |  +| | | -             |
            )|| +----/\/\-----|>|---->>----|>|----+---||||||---+          |
            )||(      33    Charging     1N4002       | | |    |  KPR139  |
            )||(      2W                           BT1         |    LB1   |
            )||(                                   3.6V, 1 A-h |    +--+  |
            )|| +-------------------->>------------------------+----|/\|--+
  AC o-----+                                             Light Bulb +--+

        |<------- Charger ---------->|<---------- Flashlight ----------->|

I could not open the transformer without dynamite but I made measurements of
open circuit voltage and short circuit current to determine the value of R1.
I assume that R1 is actually at least in part the effective series resistance
of the transformer itself.

Similar circuits are found in all sorts of inexpensive rechargeable devices.
These have no brains so they trickle charge continuously.  Aside from wasting
energy, this may not be good for the longevity of some types of batteries (but
that is another can of worms).

  7.31) Brand Unknown (Made in China) rechargeable flashlight schematic

This is another flashlight that uses NiCd batteries.  The charger is very
simple - a series capacitor to limit current followed by a bridge rectifier.

There is an added wrinkle which provides a blinking light option in addition
to the usual steady beam.  This will also activate automatically should there
be a power failure while the unit is charging if the switch is in the 'blink'

With S1 in the blink position, a simple transistor oscillator pulses the light
with the blink rate of about 1 Hz determined by C2 and R5.  Current through R6
keeps the light off if the unit is plugged into a live outlet.  (Q1 and Q2 are
equivalent to ECG159 and ECG123AP respectively.)

            R1          D1                 R3   LED1
    AC o---/\/\----+----|>|-------+---+---/\/\--|>|--+    D1-D5: 1N4002
            33    ~|    D2        |+  |   150        |
           1/2W    +----|<|----+  |   |       R4     |  D5
                        D3     |  |   +------/\/\----+--|>|--+
              C1   +----|>|----|--+   |    33, 1/2W          |   LB1 2.4V
            1.6uF ~|    D4     |      |   | |                |   +--+ .5A
    AC o--+---||---+----|<|----+--+---|--||||--------------+-+---|/\|----+
          |  250V  |              |-  | - | |+             |     +--+    |
          +--/\/\--+              |   |   BT1      + C2 -  |      R5     |
              R2                  |   |  2.4V    +---|(----|-----/\/\----+
             330K                 |   |          |  22uF   |     10K     |
                                  |   |    R6    |       |/ E            |
                                  |   +---/\/\---+-+-----| Q1            |
                                  |       15K      |     |\ C  +---------+
                                  |                /  C327 |   |         |
                                  |             R7 \   PNP |   |   1702N |
                                  |           100K /       |   |   NPN |/ C
                                  |                \       +---|-------| Q2
                                  |      On        |           |       |\ E
                                  |   S1 o---------|-----------+         |
                                  +----o->o Off    |                     |
                                    Blink/Power Fail

  7.32) Makeup mirrors

There are a simple movable mirror with incandescent or fluorescent lighting
built in.

Replacing incandescent light bulbs can usually be done without disassembly.
The bulbs may be of the specialty variety and expensive, however.

When a unit using fluorescent bulbs will no longer come on, the most likely
cause is a bad bulb.  However, replacement may involve disassembly to fain
access.  Where two bulbs are used, either one or both might be bad.  Sometimes
it will be obvious which is bad - one or both ends might be blackened.  If
this is not the case, replacement or substitution is the only sure test.  These
**will** be expensive $7-10 is not uncommon for an 8 inch fluorescent bulb!

Other possible problems: plug, cord, switch, light bulb sockets.

  7.33) Chandeliers

A chandelier is simply an incandescent light fixture with multiple sockets.
No matter how fancy and expensive, the wiring is usually very simple - all
the sockets are connected in parallel to a cord which passes through the
chain to a ceiling mounted electrical box.

If none of the lights come on, check for a blown fuse or circuit breaker,
bad wall switch or dimmer, a bad connection in the ceiling box or elsewhere
in the house wiring, or a bad connection where the cord is joined to the
individual socket wires.

Where only one bulb does not light - and it is not a burned out bulb - a
bad socket, loose wire connection at the socket, or bad connection at the
point where the wires are joined (Wire Nuts(tm) or crimps) is likely.

  7.34) Portable fans and blowers

These consist of a cordset, switch, and AC motor.  Oscillating fans add
a gearbox to automatically swivel the fan to direct air in more than one
direction.  Most are of the bladed variety though some small types might
use a squirrel cage type centrifugal blower.

There are two kinds of problems: totally dead or stuck/sluggish.

A totally dead fan can be the result of several possible causes:

* Bad cord or plug - these get abused.  Test or substitute.

* Bad power switch - bypass it and see if the fan starts working or test
  with a continuity checker or multimeter.  Sometimes, just jiggling it
  will confirm this by causing the fan to go on and off.

* Open thermal fuse in motor - overheating due to tight bearings or a motor
  problem may have blown this.  Inspect around motor windings for buried
  thermal fuse and test with continuity checker or multimeter.  Replacement
  are available.  For testing, this can be bypassed with care to see if the
  motor comes alive.

* Burned out motor - test across motor with a multimeter on the low ohms
  scale.  The resistance should be a few Ohms.  If over 1K, there is a
  break in the motor winding or an open thermal fuse.  If there is no fuse
  or the fuse is good, then the motor may be bad.  Carefully inspect for fine
  broken wires near the terminals as these can be repaired.  Otherwise, a
  new motor will be needed.  If the motor smells bad, no further investigation
  may be necessary!

* Bad wiring - check for broken wires and bad connections.

As always, your continuity checker or multimeter on the low ohms scale
is your best friend and can be used to trace the wiring from the wall plug
through all components of the appliance.

Sluggish operation can be due to gummed up lubrication in the motor or any
gears associated with an automatic oscillating mechanism.  Disassemble,
thoroughly clean, and then lubricate the motor bearings with electric motor
oil.  Use light grease for the gearbox but this is rarely a problem.

A noisy fan may be due to dry motor or other bearings or loose hardware
or sheetmetal.  Disassemble, clean, and lubricate the motor or gearbox
as above.  Inspect for loose covers or other vibrating parts - tighten
screws and/or wedge bits of wood or plastic into strategic locations to
quiet them down.  

Damaged fan blades will result in excessive vibration and noise.  These
may be easily replaceable.  They will be attached to the motor shaft with
either a large plastic 'nut' or a setscrew.  However, locating a suitable
set of blades may be difficult as many cheap fans are not made by well
known companies.

  7.35) Computer power supply (and other) fans

Virtually all of these use brushless DC motors with stationary coils and a
rotating multipole magnet which is part of the blade assembly.  Most common
problems are gummed up lubrication or worn bearings - especially for the cheap
sleeve bearing variety found in most PCs.  Occasionally, an electronic failure
will result in a dead spot or other problem.

Ball bearing fans rarely fail for mechanical reasons but if the bearings
become hard to turn or seize up, replacement will usually be needed.  (Yes,
I have disassembled ball bearings to clean and relube THEM but this used only
as a last resort.)

WARNING: For power supply fans, be aware that high voltages exist inside the
power supply case for some time (perhaps hours) after the unit is unplugged.
Take care around the BIG capacitors.  If in doubt about your abilities, leave
it to a professional or replace the entire power supply!

The only type of repair that makes sense is cleaning and lubrication.  Else,
just replace the fan or power supply.  It isn't worth troubleshooting
electronic problems in a fan!

If you want to try to clean and lubricate the bearings, the blade assembly
needs to be removed from the shaft.  There should be a little clip or split
washer holding it on.  This is located under a sticker or plastic plug on the
center of the rotating blade hub.  Once this fastener has been removed, the
blades will slide off (don't lose the various tiny spacers and washers!)

Thoroughly clean the shaft and inside the bushings and then add just a couple
drops of light oil.  Also, add a few drops of oil to any felt washers that may
be present as an oil reservoir.

Reassemble in reverse order making sure the tiny washers and spacer go back
in the proper positions.

How long this lasts is a crap shoot.  It could be minutes or years.

Replacement fans are readily available - even Radio Shack may have one that
is suitable.  Nearly all run on 12 VDC but some small CPU fans may use 5 VDC.
While current ratings may vary, this is rarely an issue as the power supply
has excess capacity.  Air flow rates may also vary depending on model but are
usually adequate for use in PCs.

  7.36) Speed control of DC fans

The small fans used in computers and peripherals usually run on 5, 12 (most
common) or 24 VDC.  Most of the time, their speed and air flow are fine for
the application.  However, is it possible to vary it should the need arise?

Usually, the answer is a qualified 'yes'.  Except for some that are internally
regulated or thermostatically controlled, the speed is affected by input
voltage.  It is likely that the fan will run on anywhere from .5 to 1.25 times
the nominal input voltage though starting when it is near the low end of this
range may need some assistance.

A universal DC wall adapter, adjustable voltage regulator, or (variable)
series power resistor can provide this control.  For example:

                     25, 2 W        + +--------+ -
    +12 VDC o-----+---/\/\---+--------| DC FAN |----o Gnd
                  |   +      |        +--------+
                  +----|(----+      12 VDC, .25 A
                    10,000 uF
                      25 V

The 25 ohms power resistor should reduce the speed of this fan by about 25 to
30 percent.  The capacitor provides full voltage for a fraction of a second to
assure reliable starting.

  7.37) Speed control of small AC fans

The following comments should also apply to many other types of appliances
using small AC motors.

These small shaded pole fans will work just fine on a Variac.  Any speed you
want, no overheating, etc.  I had done this with all sorts of little computer
cooling fans as well as larger (remember those old DEC PDP-11 rack fans?).

Small triac based speed controls like those used for ceiling fans may also
work.  Even light dimmers will *probably* work for medium size fans or banks
of fans though I cannot guarantee the reliability or safety of these.  The
problem is that small induction motors represent a highly inductive loads for
the light dimmer circuitry which is designed for a resistive load.  I have
achieved a full range of speeds but over only about 1/4 to 1/2 of the rotation
of the control knob.  There is some buzz or hum due to the chopped waveform.

However, from my experiments, light dimmers may have problems driving a single
small fan.  If the load is too small, the result may be a peak in speed (but
still way less than normal) at an intermediate position and the speed actually
much lower when on full, or reduced speed even on full.  In this case, adding
a resistive load in parallel with the motor - a light bulb for example - may
improve its range.  It adds a sort of quaint look as well! :-)

If you do opt for a solid state speed control, make sure you include a fuse
in the circuit.  A partial failure of the triac can put DC through the motor
which would result in a melt-down, lots of smoke, or worse.

The reason these simple approaches will work for these AC motors is that they
are high slip to begin with and will therefore have a high range of speed vs.
input voltage.  The only concern is overheating at some range of lower speeds
due to reduced air flow.  However, since these fans are normally protected even
against stall conditions, I wouldn't expect overheating to be a problem - but
confirm this before putting such fans into continuous service.

If all you need to do is provide a fixed, reduced speed for a bank of similar
AC fans, try rewiring them as two sets of parallel connected fans in series.
The result will be 1/2 the normal line voltage on each fan motor which may
provide exactly the speed you want!  The extension to more than 2 sets of fans
is left as an exercise for the student :-).

  7.38) Ceiling fans

While the original slow rotating ceiling mounted fan predates the widespread
use of airconditioning, there is a lot to be said for the efficiency,
effectiveness, and silence of this technology - not to mention the ambiance.

A ceiling fan is just an induction motor driving a set of blades.  Multiple
taps on the motor windings in conjunction with a selector switch provides
speed control for most inexpensive fans.  Better units include a solid state
motor speed control.

The light often included with the fan unit is usually just an incandescent
fixture with 1-5 bulbs and a switch.  This may be a simple on-off type,
a selector to turn on various combinations of bulbs, or a dimmer with
continuous or discrete control of illumination.

WARNING:  Always check mechanical integrity of fan mounting when installing
or servicing a ceiling fan.  Original design and construction is not always 
as fail-safe as one might assume.  Double check for loose nuts or other
hardware, adequate number of threads holding fan to mounting, etc.  These
have fallen without warning.  Only mount in ceiling boxes firmly anchored
to joists - not just hanging from the ceiling drywall!  Check that the
fan is tight periodically.  The constant vibration when running, slight as
it is, can gradually loosen the mounting hardware.  Furthermore, if pull
chain type switches are used for the fan or light, constant tugging can also
tend to loosen the entire fan.

Failures of ceiling fans can be divided into electrical and mechanical:


* No power - Use a circuit tester to determine if power is reaching the
  fan.  Check the fuse or circuit breaker, wall switch if any, and wire
  connections in ceiling box.

* Bad switch in fan - with power off, check with a continuity tester.  If
  wiring is obvious, bypass the switch and see if the fan comes alive.
  Jiggle the switch with power on to see if it is intermittent.  For
  multispeed fans, exact replacements may be required.  For single speed
  fans, switches should be readily available at hardware stores, home
  centers, or electrical supply houses.

* Bad or reduced value motor start/run capacitor.  This might result in
  slower than normal speed or lack of power, a fan that might only start
  if given some help, or one that will not run at all.

  For an existing installation that suddenly stopped working, a bad cap is
  a likely possibility.  An induction motor that will not start but will
  run once started by hand usually indicates a loss of power to the starting
  (phase) winding which could be an open or reduced value capacitor.

  This is probably a capacitor-run type of motor where the capacitor provides
  additional torque while running as well.  Therefore, even starting it
  by hand with the blades attached might not work.  With the blades removed,
  it would probably continue to run.  Of course, this isn't terribly useful!

* Bad motor - if all speeds are dead, this would imply a bad connection
  or burned winding common to all speeds.  There might be an open thermal
  fuse - examine in and around the motor windings.  A charred smelly
  motor may not require further testing.  A partially shorted motor may
  blow a fuse or trip a circuit breaker as well or result in a loud hum
  and no or slow operation as well.


* Noise and/or vibration - check that fan blades are tight and that any
  balance weights have not fallen off.  Check for worn or dry bearings.
  Check for sheetmetal parts that is loose or vibrating against other parts.
  Tighten screws and/or wedge bits of plastic or wood into strategic spots
  to quiet it down.  However, this may be a symptom of an unbalanced fan,
  loose fan blade, or electrical problems as well.  Check that no part of
  the rotating blade assembly is scraping due to a loose or dislodged

* Sluggish operation - blades should turn perfectly freely with power off.
  If this is not the case, the bearings are gummed up or otherwise defective.
  Something may be loose and contacting the casing.  (This would probably
  make a scraping noise as well, however).

  7.39) Lubricating ceiling fans

(From: Chris Chubb (cchubb@ida.org)).

I use synthetic transmission lube, 80-130 (manual gearbox, not automatic
transmission fluid which is very thin --- sam).  I imagine that any similar
lubricant, synthetic or not, would work as well, but the synthetic flows down
in better and works well.

Do not use WD-40, 3-in-1 oil or any other lightweight oil. Motor oil is good
as well, but it does not stick to the bearings as well.  DO NOT use automatic
transmission fluid - extremely thin.

Grease would be perfect, white lithium, divine!  But, getting the grease
down into the bearings would be very difficult.

Just about three or four drops should be all it takes. Getting it
on the lower bearings of the ceiling fan will be tough. I have an
oil can that I pump a drop to the tip of, then hold it against the 
bearings until they wick the oil inside. This is very slow. It takes
about 15 minutes per fan to oil, clean the top of the blades, oil
a little around the hanging ball, pull the globe off and clean 
the globe inside, and make sure everything is OK. 

  7.40) Variable speed ceiling fan on normal circuit

It is usually not possible to use a normal light dimmer to control the fan
as this uses an AC induction motor.  A dimmer can only be used on the built
in light if a separate wire is available to power it.

Doing this will likely result in a nasty hum or buzz at anything other than
full brightness (speed) or off.  This is both annoying and probably not good
for the fan motor as well.  A dimmer works by reducing the power to the
light by controlling when the voltage is applied on each cycle of the AC.  If
it is turned on half way through the cycle half the power is provided, for
example.  However, with cheap lamp dimmers, this results in sharp edges on
the waveform rather as peak voltage is applied suddenly rather than with the
nice smooth sinusoid.  It is these sharp edges causing the coils or other
parts of the fan to vibrate at 120 Hz that you are hearing.

Special speed controls designed for ceiling fans are available - check your
local home center or ceiling fan supplier.

Here is another alternative:

(From: Rick & Andrea Lang (rglang@radix.net)).

Here's a potential solution if you don't mind spending a little more for 
a ceiling fan (If you already have one in that location, perhaps you can put
it in another room).  Ceiling fans with remote control are now available. 
They only require power to the ceiling fan (2 wire) and a remote 
control. With the remote you can dim the lights, slow the fan or both. 
You can then use the existing new wall switch as a power ON/OFF switch 
also. If you choose this route, be careful of interference with garage 
door openers. Usually, the remotes have at least 4 frequency selections 
to help avoid interference with other remote systems. I put one in that 
three of the four frequencies opened the garage door. I lucked out on
the 4th one!

  7.41) Throbbing noise from ceiling fan

This could be due to a mechanical problem - bad bearings or blades out of
balance - or an electrical problem with the speed control.

(From: David Buxton (David.Buxton@tek.com)).

A quickie test.  Get the fan turning at a speed that demonstrates the 
throbbing noise.  Come up with a way to instantly remove power to the 
fan.  If the noise continues for a little bit until the fan has slowed 
down enough, then you know the noise is in the mechanical dynamics, 
perhaps blades out of balance.  If the noise quits instantly with power 
removal, then you need a better speed control better designed for fan 
motor control.

  7.42) Ceiling fan motor speed control and capacitor replacement

(From: Kevin Astir (kferguson@aquilagroup.com)).

Ceiling fans are normally multipole, capacitor-run  types.  They normally
run fairly close to stalled, the blades being big enough that the motor
never gets anywhere near synchronous speed.

Speed control in three speed types is by switching the value of the cap
in series with the quadrature windings. The caps normally have two
sections of 3 and 6 uF,  with a common connection between the two
sections allowing connections of 3, 6, or 9 (3 in parallel with 6) uF

I have seen some caps of slightly different value, but they should be
close, just translate my 3 and 6 to what you actually have in what

The higher the capacitance the higher the stall torque, so the faster
the fan runs against the non-linear (square-law) torque vs. speed
characteristic of the blades. (remember I said it is always pretty
much stalled)

If you miswired the cap, then you may be getting 3 or 6 and 2 (3 in
*series*  with 6 uF which would result in low speeds.  This *is* the
case if any 2 out of 3 speeds seem to be the same. The replacement caps
are usually marked with what terminal is which, but originals often are
not.  I don't know if there is a standard color code, but manufacturers
are under no obligation to adhere to it even if there was.  If you are
totally lost, there are only 6 possible ways to connect the capacitor.
2 of these will give you all 3 speeds (but one in wrong order).  So if
you keep good notes (essential here) then you could try all possibilities
in 20 minutes or so...yes, you're probably working with hands over head,
what you wanted easy too?

OK, here is how to get it in 3 tries max:

Identify the "common"  capacitor lead  (connects to both 3, and 6 uF
sections, hopefully your replacement is marked). It is currently
connected to the wrong place, so swap it with one of the other cap
wires.  If you now have three speeds in the correct order, then your
done.  If you have three speeds in the wrong order, then leave common
wire alone, but swap other two. (correct order is: off-hi-med-lo

If you *didn't* have three different speeds following the first wire
swap, then swap that common wire with the one wire you haven't moved
yet. Now you should have three speeds, now correct the order as
described, if needed.

If you currently have three speeds, but all are too slow, then it is
likely that your fan needed a higher value capacitor. another
explanation might be that the old cap was getting leaky when it
warmed up after start, and letting the fan have extra current, thus
giving extra speed.

In my experience, the three speed types should run from just slow
enough to follow with the eye, to fast, fairly noisy, and making a
fair amount of wobble on the mounting.

Continuously variable speed types put a  fixed 9 or 10 uF cap in
series with the quadrature winding, and regulate voltage to both
windings via lamp-dimmer style triac circuit.

  7.43) Mike's notes on ceiling fan installation

(From: morris@cogent.net (Mike Morris)).

Depending on what wiring you have and what new wiring needs to be installed,
I would install 14/3 cables for all ceiling lights. That way, you will be able
to control ceiling fan and light from two separate switches.

Each time a new light has to be installed in our house, I make sure a 14/3
wire is installed. For three-way switches, I make it two 14/3 wires, even
if I don't install a ceiling fan now. A 14/3 wire is not that much more
expensive, and 10 years down the road, it might be useful.

The local high-end lights-and-fans shops have a handout that recommends
that wherever a ceiling fan is to go have the following wiring:

1. Neutral

2. Ground (if local code requires it, good idea anyway)

3. Switched hot for the lights

4. Switched hot for the fan

5. An extra wire - some brands need 2 hots for the fan, and
   if your brand doesn't need it, an extra conductor doesn't hurt.

Why two switched hots?

* It allows to run the lights and fan separately. 

* You should not use a lamp dimmer as a motor speed control.  While it may
  work to some extent, the motor will likely hum and long term reliability
  and safety are questionable.

Note that this does not preclude using a fan with built-in controls - unused 
wire is just that. And pulling in 5 conductors during construction or 
remodeling costs just a little more that pulling in 2 or 3.

The handout sheet also point out that adding a extra brace to the ceiling 
during any remodeling or new construction sized for a 100 pound dead weight
is a good idea - it can be as simple as a couple of feet of 2x6" lumber and a 
couple of sheet metal fasteners. A wobbling fan can cause fatigue in a light 
duty metal brace rapidly.  The extra cost is minimal, and it can prevent a fan 
from landing in the middle of the bed! 

  7.44) Air cleaners

Simple air cleaners are just a motor driven fan and a foam or other filter
material.  HEPA (High Efficiency Particulate Air) types use higher quality
filters and/or additional filters and sealed plenums to trap particles down to
a specified size (.3 micron).  A clogged (neglected) filter in any air cleaner
is probably the most likely problem to affect these simple devices.  Failure
of the fan to operate can be a result of any of the causes listed above in the
section: "Portable fans and blowers".

Electronic air cleaners include a high voltage low current power supply and
oppositely charged grids in the air flow. A failure of the solid state high
voltage generator can result in the unit blowing air but not removing dust and
particulate matter as it should.  A typical unit might have 7.5 to 10 KV at
100 uA maximum (short circuit current, probably less at full voltage).  Actual
current used is negligible under normal conditions.  This voltage is
significant but the current would be just barely detectable, if at all.

The modules are usually quite simple: a transistor or other type of switching
circuit driving a step-up transformer and possibly a diode-capacitor voltage
multiplier.  See the sections: "Electronic air cleaner high voltage module
schematic" and "Auto air purifier schematic" for an example
of a typical circuit.

Where there is no high voltage from such a device, check the following:

* Make sure power is actually getting to the high voltage portion of the unit.
  Test the wall socket and/or AC adapter or other power supply for proper
  voltage with a multimeter.

* Excessive dirt/dust/muck/moisture or physical damage or a misplaced paper
  clip may be shorting it out or resulting in arcing or corona (a strong aroma
  of ozone would be an indication of this).  With such a small available
  current (only uA) it doesn't take much for contamination to be a problem.
  Thoroughly clean and dry the unit and check for shorts (with a multimeter
  between the HV electrodes and case) and then test it again.  Your problems
  may be gone!

* If this doesn't help and the unit is not fully potted (in which case,
  replacement is the only option), check for shorted or open components,
  especially the power semiconductors.

  7.45) Electronic air cleaner high voltage module schematic

At least I assume this cute little circuit board is for an electronic air
cleaner or something similar (dust precipitator, positive/negative ion
generator, etc.)!  I received the unit (no markings) by mistake in the mail.
However, I did check to make sure it wasn't a bomb before applying power. :-)

This module produces both positive and negative outputs when connected to 115
VAC, 60 Hz line voltage.  Each is about 5 KV at up to around 5 uA.

The AC line powered driver and HV multiplier are shown in the two diagrams,

                   D1                                            T1  o
  H o--------------|>|----+---+--------------------+                +-----o A
                 1N4007   |   |        Sidac     __|__ SCR1     |:|(
                          |   |   R3  D2 100 V   _\_/_ T106B2   |:|(
  AC                  C1  |   +--/\/\---|>|      / |   200 V    |:|(
 Line      Power  .15 uF _|_     1.5K   |<|--+--'  |   4 A    o |:|( 350 ohms
          IL1 LED   250V ---                _|_    |  +-------+ |:|(
        +--|<|---+        |              C2 ---    |  |        )|:|(
        |   R1   |   R2   |        .0047 uF  |     |  | .1 ohm )|:|(
  N o---+--/\/\--+--/\/\--+                  +-----+--+        )|:|(
           470      3.9K  |                                +--+     +--+--o B
           1 W      2 W   |                                |    R4     |

The AC input is rectified by D1 and as it builds up past the threshold of the
sidac (D2, 100 V), SCR1 is triggered dumping a small energy storage capacitor
(C1) through the primary of the HV transformer, T1.  This generates a HV pulse
in the secondary.  In about .5 ms, the current drops low enough such that the
SCR turns off.  As long as the instantaneous input voltage remains above about
100 V, this sequence of events repeats producing a burst of 5 or 6 discharges
per cycle of the 60 Hz AC input separated by approximately 13 ms of dead time.

The LED (IL1) is a power-on indicator. :-)

The transformer was totally potted so I could not easily determine anything
about its construction other than its winding resistances and turns ratio
(about 1:100).

                                            A o
                                     C3       |
          R5     R6      D3   |   D4     D5   |  D6     R7       R8
  HV- o--/\/\---/\/\--+--|>|--+--|>|--+--|>|--+--|>|---/\/\--+--/\/\--o HV+
         10M    10M   |      C4       |                220K  |  10M
                      +------||-------+                      |
       D3-D6: 10 KV, 5 mA            _|_                    _|_
       C3,C4: 200 pF, 10 KV          --- C5                 --- C6
       C5,C6: 200 pF, 5 KV            |                      |
                                 B o--+----------------------+

The secondary side consists of a voltage tripler for the negative output
(HV-) and a simple rectifier for the positive output (HV+).  This asymmetry is
due to the nature of the unidirectional drive to the transformer primary.

From my measurements, this circuit produces a total of around 10 KV between
HV+ and HV-, at up to 5 uA.  The output voltages are roughly equal plus and
minus when referenced to point B.

I assume the module would also operate on DC (say, 110 to 150 V) with the
discharges repeating continuously at about 2 KHz.  Output current capability
would be about 5 times greater but at the same maximum (no load) voltage.
(However, with DC, if the SCR ever got stuck in an 'on' state, it would be
stuck there since there would be no AC zero crossings to force it off.  This
wouldn't be good!)

  7.46) Auto air purifier schematic

Well, maybe :-).  This thing is about the size of a hot-dog and plugs
into the cigarette lighter socket.  It produces a bit of ozone and who knows
what else.  Whether there is any effect on air quality (beneficial or
otherwise) or any other effects is questionable but it does contain a nice
little high voltage circuit.

                                                                   DL1 +-+ |
                                                   o  T1 +-------+-----|o|
  +12 o---+--------+----------+---------------------+ ||(        |     +-+ |
          |        |          |                D 30T )||(        | DL2 +-+
          |        |        -_|_ 4.7uF           #30 )||(        +-----|o| |
          |        |         --- 50V         +------+ ||( 3000T  |     +-+
          |       _|_ C2    + |              |        ||( #44    | DL3 +-+ |
          |       --- 470pF   +--------------|------+ ||(        +-----|o|
          |        |          |              | F 30T )||(        |     +-+ |
        +_|_ C1    |          |       D1     |   #36 )||(        | DL4 +-+
         --- 33uF  +----------|---+---|<|----|------+ ||(        +-----|o| |
        - |  16V   |          |   | 1N4002   |     o     +--+          +-+
          |        /          /   |        |/ C           o |              | 
          |     R1 \       R2 \   +--------|Q1  TIP41       +--------------+
          |     1K /     4.7K /            |\ E             |            Grid
          |        \          \              |              |
          |        |          |              |              |
  GND o---+--------+----------+--------------+--------------+

T1 is constructed on a 1/4" diameter ferrite core.  The D (Drive) and F
(Feedback) windings are wound bifilar style (interleaved) directly on the
core.  The O (Output) winding is wound on a nylon sleeve which slips over
the core and is split into 10 sections with an equal number of turns (100
each) with insulation in between them.

DL1 to DL4 look like neon light bulbs with a single electrode.  They glow like
neon light bulbs when the circuit is powered and seem to capacitively couple
the HV pulses to the grounded grid in such a way to generate ozone.  I don't
know if they are filled with special gas or are just weird neon light bulbs.

  7.47) Bug zappers

You know the type - a purplish light with an occasional (or constant) Zap!
Zap! Zap!  If you listen real closely, you may be able to hear the screams of
the unfortunate insects as well :-).

The high-tech versions consist of a high voltage low current power supply and
fluorescent (usually) lamp selected to attract undesirable flying creatures.
(Boring low-tech devices may just use a fan to direct the insects to a tray of
water from which they are too stupid to be able to excape!)

However, these devices are not selective and will obliterate friendly and
useful bugs as well as unwanted pests.

Here is a typical circuit:

         S1        R1         C1            C2            C1-C4: .5 uF, 400 V
  H o----o/ o--+--/\/\--------||---+--------||---------+  D1-D5: 1N4007
               |  25K        D1    |   D2        D3    |   D4
               |         +---|>|---+---|>|---+---|>|---+---|>|---+
              +-+        |        C3         |        C4         |
 AC Line      |o| FL1    +---+----||----+----+---+----)|----+----+--o + 
              +-+ Lamp   |   |    R3    |        |    R4    |        500 to
               |         |   +---/\/\---+        +---/\/\---+        600 V
               |   R2    |       10M                 10M             to grid
  N o----------+--/\/\---+------------------------------------------o -

This is just a line powered voltage quadrupler.  R1 and R2 provide current
limiting when the strike occurs (and should someone come in contact with the
grid).  The lamp, FL1, includes the fluorescent bulb, ballast, and starter (if
required).  Devices designed for jumbo size bugs (or small rodents) may use
slightly larger capacitors!

(From: Jan Panteltje (pante@pi.net)).

I have one, bought it very cheap: they are only $10 here :)

It comes with a 25 W blue lamp inside, with wires around it.  The lamp did not
last long, so I replaced that with a 7 W electronic fluorescent type, that now
just keeps going and going and going.  The bugs do not care, they just go for
the light.  Then they hit the wires.

Here, we have 230 V, in the lamp is a voltage doubler, with 2, 220 nF
capacitors, 2 silicon diodes, and a 10 K Ohm series resistor in the mains.
The whole thing cannot be touched by humans from outside.  The voltage between
the wires is something like 620 V.  If an insect shorts the wires, the 10K
limits the current until it is destroyed (the insect that is).  The insect
actually explodes, the 600 V cap discharges into it.

  7.48) Electric fences

Yes, I know, this isn't a common small appliance but....

(From: John Harvey (johnharvey@bigpond.com)).

Most DIY fence energizers use an automotive ignition coil and kits (generally
minus coil) are available in Australia and probably elsewhere.

Commercial units operate on the capacitor discharge principle and are fired at
a 1.2 second interval.  Voltage O/P needs to be around 5 to 8 KV (which will
drop under load).  The energy O/P (pulse duration) is determined by the
capacitor and 10 to 20 uF is about right for a small unit (up to 2km or so).
They must use a pulse grade capacitor (which has a high dV/dt) to be reliable.

  7.49) Appliance and light timers

There are two basic types: mechanical and electronic.

* Mechanical timers are simply a synchronous timing motor and gear reducer
  controlling a two prong (usually polarized) outlet.

  The most common problems relate to failure of the timing motor or gear
  train.  With time, the oil and grease used inside the timing motor may
  gum up.  Eventually, it gets so stiff that the motor stops - or more likely -
  doesn't start up after a power failure or the unit has been unplugged for
  a while.

  The cheap plastic gears may also break, chip, or loose teeth.

  Sometimes, disassembly, cleaning, and lubrication, will get the motor
  going - possibly for a long time.  However, replacement parts are rarely
  worth the cost compared to a complete new timer.

* Fully electronic timers use digital clock-type circuitry to control a triac
  or other solid state switching device.

  These may fail in the same way as other electronic controls such as dimmers.
  Most likely problems are that they are either stuck off or stuck on.  Aside
  from testing for bad connections or shorted or open components (with power
  OFF or disconnected!), repair is probably economical.  Assuming it can be
  opened non-destructively at all, check the triac and other parts in its
  vicinity.  The rest of the circuitry is probably in a proprietary chip - but
  these don't fail much.

  Also see the section:
  "Warnings about using compact fluorescent lamps on electronic timers".

  7.50) Warnings about using compact fluorescent lamps on electronic timers

You may have seen these warnings in the instructions or on the package of
electronic (not mechanical) timers and/or compact fluorescents.

There are two issues:

1. Providing the trickle current to operate the clock circuitry in the timer.

   Where a solid state timer is used to replace a normal switch, there is
   usually no connection to the Neutral so it must derive all its operating
   power from current through the load (though at a very low current level).

   The type of circuitry in a compact fluorescent with an electronic ballast
   (or other equipment with a switching power supply like a TV, some VCRs,
   computer, etc.) may result in this current being too low or erratic.  The
   result will be that the timer doesn't work properly but damage isn't that
   likely (but no guarantees).

   If it is installed with 3 wires (Hot, Neutral, Load), then this should not
   be a problem.

   In addition, interference (e.g., spikes) from the CF ballast may feed back
   into the electronic timer and this may either confuse or actually result
   in failure.

2. Damage to either or both of the devices dues to incompatibility.

   The solid state switching device - usually a triac - in the timer unit
   may be blown by voltage spikes or current surges when the power goes on or
   off into an inductive or capacitive load like an electronic ballast (or
   normal magnetic ballast, for that matter.

In short, read and follow label directions!  Although a given combination may
actually work reliably for years even if it is not supposed to but you should
be able to find a pair for which this shouldn't be a problem.

  7.51) Wall thermostats

These can be divided into several classes depending on:

* Normal or setback (electronic or electromechanical).
* 24 VAC or self powered (thermopile or thermocouple) valve control.
* Heating, airconditioning, or combination.

It is not possible to cover all variations as that would require a
complete text in itself.  However, here is a summary of possible
problems and solutions.

Conventional thermostats usually use a bimetal strip or coil with a
set of exposed contacts or a mercury switch.  In general, these are
quite reliable since the load (a relay) is small and wear due to
electrical arcing is negligible.  On those with exposed contacts, dirt
or a sliver of something can prevent a proper connection so this is
one thing to check if operation is erratic.  The following description
assumes a single use system - heating or cooling - using 24 VAC control
which is not properly controlling the furnace or airconditioner.

1. Locate the switched terminals on the thermostat.  Jumper across them
   to see if the furnace or airconditioner switches on.  If it does, the
   problem is in the thermostat.  If nothing happens, there may be a
   problem in the load or its control circuits.  Cycle the temperature dial
   back and forth a few times to see if the contacts ever activate.  You
   should be able to see the contacts open and close (exposed or mercury)
   as well.

   (CAUTION: on an airconditioner, rapid cycling is bad and may result in
   tripped breakers or overload protectors so ideally, this should be done
   with the compressor breaker off).

2. Check for 24 VAC (most cases) across the switched circuit.  If this
   is not present, locate the control transformer and determine if it
   is working - it is powered and its output is live - you may have the
   main power switch off or it may be on a circuit with a blown fuse or
   tripped breaker.  I have seen cases where the heating system was on
   the same circuit as a sump pump and when this seized up, the fuse blew
   rendering the heating system inoperative.  Needless to say, this is not
   a recommended wiring practice.  The transformer may be bad if there is
   no output but it is powered.  Remove its output connections just to make
   sure there is no short circuit and measure on the transformer again.

3. If 24 VAC is present and jumpering across the terminals does nothing,
   the heater valve or relay or airconditioner relay may be bad or there
   is a problem elsewhere in the system.

4. Where jumpering the terminals turns on the system, the thermostat contacts
   may be malfunctioning due to dirt, corrosion, wear, or a bad connection.
   For a setback unit, the setback mechanism may be defective.  Test and/or
   replace any batteries and double check the programming as well.  On
   those with motor driven timers operating off of AC, this power may be

5. Where jumpering the terminals does not activate the system, check the 
   load.  For a simple heating system, this will be a relay or valve.  Try
   to listen for the click of the relay or valve.  If there is none, its
   coil may be open though in this case there will be no voltage across the
   thermostat contacts but the 24 V transformer will be live.  If you
   can locate the relay or valve itself, check its coil with an ohmmeter.

6. If the previous tests are ok, there may be bad connections in the wiring.

Type of control - most systems use a 24 VAC circuit for control.  However,
some use low voltage self powered circuits that require special compatible
(sometimes called thermopile or thermocouple) thermostats with low resistance
contacts and no electronics directly in series with the control wires.
Erratic or improper control may result from using the wrong type.

Setback thermostats - these may be controlled electromechanically by a
timer mechanism which alters the position of the contacts or selects
an alternate set.  Newer models are fully electronic and anything beyond
obvious bad connections or wiring, or dead batteries is probably not
easily repaired.  However, eliminate external problems first - some of
these may need an additional unswitched 24 VAC or 115 VAC to function
and this might be missing.

Heat anticipators - in order to reduce the temperature swings of the heated
space, there is usually a small heating element built into the thermostat
which provides some more immediate feedback to the sensor than would be
possible simply waiting for the furnace to heat the air or radiators.  If
this coil is defective or its setting is misadjusted, then erratic or much
wider than normal temperature swings are possible.  There will usually be
instructions for properly setting the heat anticipator with the thermostat
or furnace.

Units that control both heating and airconditioning are more complex and
will have additional switches and contacts but operate in a similar manner
and are subject to similar ailments.

  7.52) Electric space heaters

All types have one thing in common - they are nearly 100% efficient which
means that just about every watt of power utilized is turned into heat.
The remainder is used for any built in fans or the wasted light produced
by glowing elements or quart lamps.

However, this does not mean that these are the most economical heating
devices.  Heat pumps based on refrigeration technology can be much less
costly to run since they can have coefficients of performance - the ratio
of heat output to energy input - of 3 or more to 1.  Thus, they are in
effect, 300% or more efficient.  Note that this does not violate any
conservation of energy principles as these simply move heat from one place
to another - the outdoors is being cooled off at the same time.

Space heaters come in 3 common varieties:

* Radiant - heating element with polished reflector.
* Convection - heating element and small fan to circulate heated air.
* Oil filled radiator - heating element heats oil and metal fins.

Problems with space heaters are nearly always related to bad heating elements,
problems with the thermostat, interlock switches, or fan (if any), or bad
connections.  Blown fuses or tripped circuit breakers are very common with
these appliances as they are heavy loads - often the maximum that can safely
be plugged into a 15 A outlet - and thus overloads are practically assured
if **anything** else is used on the same circuit.  Since we rarely keep
track of exactly what outlets are on any given circuit, accidentally using
other devices at the same time are likely since the same circuit may feed
outlets in more than one room - and sometimes some pretty unlikely places.

  7.53) Radiant space heaters

These use a coiled NiChrome, Calrod(tm), or quartz lamp heating element.
There is no fan.  A polished reflector directs the infra red heat energy
out into the room.  Radiant space heaters are good for spot heating of
people or things.  They do not heat the air except by convection from the
heated surfaces.

Of course, first check that the outlet is live.

As with other heating appliances, the most likely problems are with burned
out heating elements; defective on/off switches, thermostats, or safety
interlock or tip-over switches, bad cord or plug, or bad wiring connections.
Your continuity checker or ohmmeter will quickly be able to identify which
of these are the problem.

Warning: do not be tempted to bypass any interlock or tip-over switches
should they prove defective.  They serve a very important fire and personal
safety function.  Never, ever cover the heater in any way as a serious fire
hazard will result.

  7.54) Convection space heaters

A small fan blows air over or through a heating element.  This may be a
NiChrome coil, Calrod(tm) element, or ceramic thermistor.  This type
is probably the most popular since it can quickly heat a small area.
The ceramic variety are considered safer than the others (of this type)
since they are supposed to operate at a lower surface temperature.

In addition to the problems covered in the section above:
"Radiant space
heaters", the fan can also become sluggish or seize up due to
gummed up lubrication (as well as other fan-motor problems).  Since
it is running in a high temperature environment, disassembly, cleaning,
and lubrication may be needed periodically despite what the manufacturer
may say about permanently lubricated parts.

  7.55) Oil filled electric radiators

These are also considered convection heaters but they do not have any fan.

The typical unit consists of a pair of heating elements providing 600, 900,
or 1500 Watts depending on which are switched on.  A simple bimetal
adjustable thermostat is used for temperature control.  The heating
elements are fully submerged and sealed inside an oil filled metal finned
replica of an old style radiator.  The whole affair is mounted on wheels
as it is quite heavy.

Common problems with these have been the pair of power switches which tend
to fail resulting in no or erratic operation.  Note: if your heater is a
Delongi, there has been a free (well $5 S&H) upgrade to replace the failure
prone power switches and thermostat on some common models.

The heating elements are replaceable (as a set).  Since they are immersed in
the oil, you MUST have the radiator on its end with the terminals straight up
while changing them or else there will be a mess.  Replacement will be worth
the cost and effort only if you require the high settings as it is unlikely
for both elements to fail.  If testing reveals an open element, you will just
not have the heat ranges that use it.  If an element shorts to the case, it
must be disconnected to prevent a shock hazard though the other one can still
be safely used.  Parts should be available.

  7.56) So, what about the Pelonus Disk furnace?

(From: Kirk Kerekes (kkereke@iamerica.net)).

It is a portable electric heater, using high-power thermisters as the heating
elements. This technology was originally developed by TDK a few decades ago.
The premise is that the power thermisters will automatically control the
heating element temperature (the thermister), so that if the air flow is
blocked, the heater won't cook. The manufacturers make efficiency claims, but
these seem to be bogus.  (All space heaters are nearly 100% efficient.  See
the section: "Electric space heaters" --- sam.)

I have a bathroom version of this device, and it works.

  7.57) Electric pencil sharpeners

AC powered pencil sharpeners consist of a small shaded pole induction
motor, pencil sense switch, and some gears and cutter wheels.  Aside
from pencil shavings crudding up the works - which can be cleaned - the
most common failure is of the cheap plastic gears.  These can be easily
be replaced if you can get them - the original manufacturer is likely the
only source.  The switch contacts may become dirty or level/bar may become
misaligned or worn.  Some clever repositioning or the addition of a shim
may help in these cases.

Battery operated pencil sharpeners use a small DC motor for power.  These
tend to be whimpier than their AC counterparts but all other comments
apply.  Always try a fresh set of batteries first.

  7.58) Blenders

A blender really is just a high speed motor mounted inside a base.  Units
with 324 speeds accomplish (this more or less useless marketing gimmick)
through a combination of diodes, resistors, and multiple windings on the
motor.  Without addressing the ultimate utility of thousands of speeds,
problems with these units are more likely to be in the motor itself - open
or shorted windings, or bad bearings.  However, the selector switches and
electrical parts can fail as well.

The motors are typically of the series wound universal type.  These have
carbon brushes which are prone to wear.  However, given the relatively short
total usage of a blender, this is not usually a problem.

Disconnecting (and labeling!) connections one at a time may permit the
source of a problem to be localized.  Diodes can be tested with a multimeter
(they should read open in one and only one direction) and resistors checked
as well.  Shorts in a motor with multiple taps on its windings may be
difficult to identify or locate.  Shorted windings can result in overheating,
incorrect speeds, or even a blender that runs with the power switch supposedly
in the off position as the wiring is sometimes sort of strange!

Bad bearings will result in any number of mechanical problems including
excessive or spine tingling noise, vibration, a seized rotor or very sluggish
rotation.  Sometimes, disassembly, cleaning, and oiling will be effective
but since these rotate at high speed, don't count on it.  Unfortunately,
cheap bronze bushings are often used instead of ball bearings.  However,
substituting a set from another similar unit might work since it is usually
the bronze bushing and not the motor shaft that fails.

The most sophisticated units will have a variable speed control - similar
to a light dimmer.  If this goes bad - the blender always runs at full
speed - then the active element (triac) has probably blown.  Replacement
is possible and the part types should be readily available.

  7.59) Drip coffee makers

A drip coffee maker consists of several components:

1. A heating element - combined or separate Calrod(tm, usually) types
   for operating the drip pump and then keeping the coffee warm.

2. Thermal protector - to prevent excess temperatures.

3. Some kind of water interlock - prevents dripping when separate reservoir
   is used.

4. Timer or controller.  The simplest are mechanical while programmable
   units with clocks and electronic timers are also available.

Many problems are be mechanical - clogged water passages or interlock.
Extended use with hard/high mineral content water can also result in reduced
heating effectiveness and/or increased heating times.  It may be possible to
flush the unit a couple of times with viniger.

If there is no heating, check the element and thermal protector with an
ohmmeter.  If the element is open, it is probably time for a new coffee maker.
The thermal protectors can be replaced but the underlying cause may be a
defective, shorted overheating element so it may not be worth the trouble.
Timers can develop bad contacts and bad connections are possible on electronic
controller circuit board wiring.

  7.60) Drop coffee maker repair

(From: Niels Henriksen (ap294@FreeNet.Carleton.CA)).

I wish I had thought of this sooner rather than throwing out the first 
coffee maker and I had planned to throw this one out.  For some reason I 
thought I would just look inside to see what was up.

Where I live the water is hard (well) and there is constant scaling and 
buildup of calcium.  We heard that all you have to do is to run a 
mixture of vinegar through the coffee maker to rejuvenate.

A friend and the 2 of ours all started to leak very badly when the 
vinegar/water mixture when through.  I though that the internal plumbing 
had corroded through the metal parts and the vinegar dissolved the 
calcium that was protecting the holes and therefore unrepairable. Who 
knows where these ideas come from.

Now for the technical solution.

The element that is used to boil the water and uses the bubbles to bring 
hot water to top of coffee maker is the same element that is used to 
keep the pot warm.

There is a metal tube attached to the metal warming element and this 
unit has a heating element embedded. There are 2 rubber hoses attached. 
One brings cold water to heater and the other brings boiling water to 
top. The cold water tube has a check valve that prevents the bubbling 
water from going to cold water reservoir.

When vinegar is added the calcium scales start to dissolve and in 3 of 3 
so far, this blocked the metal tube.  The water starts to boil and since 
the cold water inlet has a check valve the water pressure can only 
buildup to where the rubber tube is blown off the metal pipe.
No damage to parts.

To fix:

1. Take bottom off to gain access to heater area.

2. Remove rubber tubes which are connected with spring clamps.

3. Run rubber tubes through your fingers to loosen scale buildup and flush out

4. push a thin copper wire or other bendable wire through heating tube.  This
   is to unblock and loosen some scale.

5. Pour straight vinegar into metal tube to dissolve calcium and use wire to

6. Repeat several times till clean.

7. Re-attach all parts and use.

The solution is to start a regular process of using vinegar BEFORE the
calcium has buildup to the point where when loosened it will block the tube.

  7.61) Coffee percolators

While largely replaced by the drip coffee maker, these are still available,
particularly in large sizes.  The components are similar to those in a
drip coffee maker - element, thermal protector, possibly a thermostat
as well.  The element and bottom of the water/coffee container are likely
one piece to provide the best thermal conduction for the 'pump' in the
middle.  Even if the element is removable, it may not be worth the cost
of replacement except for a large expensive unit.

  7.62) Electric kettles

These consist of a heating element, thermal protector, and possibly a
thermostat and/or timer.  See comments for coffee makers.

  7.63) Electric (motor driven) clocks

While line operated clocks have mostly been superseded by electronic
(LED or LCD) clocks on nearly every kitchen appliance, many of these
are still in operation on older clock radios and ranges.

AC operated clocks depend on the AC line frequency (60 Hz or 50 Hz
depending on where you live) for time keeping.  The accuracy of a
line operated clock is better than almost any quartz clock since 
the long term precision of the power line frequency is a very carefully
controlled parameter and ultimately based on an atomic clock time standard.

Therefore, most problems are related to a clock motor that does not run or
will not start up following a power outage.  Once running, these rarely fail.

The most common problems are either gummed up oil or grease inside the
motor and gear train, broken gears, or broken parts of the clock mechanism
itself.  See the sections on "Synchronous timing motors" for repair info.

Battery operated quartz clocks usually operate on a 1.5 V Alkaline cell
(do not replace with NiCds as they do not have a long absolute life
between charges even if the current drain is small as it is with a clock).

First, test the battery.  Use a multimeter - usually anything greater than
1 V or so will power the clock though if it is closer to 1 V than 1.5 V,
the battery is near the end of its life.  The clock may run slow or fast
or erratically on a low battery.

With a good battery, failure to run properly is usually mechanical - one
of the hands is hitting against the glass front or something like that.
Don't forget to check any on/off switch - these are not expected but are
often present presumably to permit you to start the clock at precisely the
right time.  I had one case where the fine wire to the solenoid that
operates the once per second clock mechanism broke and had to be resoldered
but this is exceedingly rare.

If the clock consistently runs slow or fast with a known good battery,
there is usually a trimmer capacitor that can be adjusted with a fine
jeweler's straight blade screwdriver.  Without test equipment the best
you can do is trial and error - mark its original position and turn it
just a hair in one direction.  Wait a day or week and see if further
adjustment is needed (right, like you also won the lottery!) and fine
tune it.

If the hands should fall off (what a thought!), they can usually be pressed
back in place.  Then, the only trick is to line up the alarm hand with the
others so that the alarm will go off at the correct time.  This can usually
be done easily by turning the hour hand counterclockwise using the setting
knob in the rear until it is not possible to turn it further.  At this point,
it is lined up with the alarm hand.  Install all hands at the 12:00 position
and you should be more or less all set.

  7.64) Rotisseries

The mechanism consists of a shaded pole induction motor and gear train.
Clean and lubricate the gears.  See the section:
"Shaded pole induction motors" for motor problems.

  7.65) Electric can openers and knife sharpeners

There consist of a shaded pole induction motor, gear train. and power
switch.  Likely problems relate to broken gear teeth, dirty or worn
power switch, dull cutting wheel, and broken parts.  Lubrication may
be needed if operation is sluggish.  Parts that come in contact with
the cans and lids collect a lot of food grime and should be cleaned

  7.66) Electric carving knives

A small motor operates a pair of reciprocating mounts for the blades.

AC powered carving knives include a momentary power switch, small motor
(probably universal type), and some gearing.  Congealed food goo as well
as normal lubrication problems are common.  The power switch is often
cheaply made and prone to failure as well.  The cord may be abused (hopefully
not cut or damaged by careless use of the knife!) and result in an intermittent
connection at one end or the other.  For motor problems, see the appropriate
sections on universal motors.

For battery powered knives, bad NiCds cells are a very likely possibility due
to the occasional use of this type of appliance.

See the section: "Small permanent magnet DC motors" and the chapter:
"Batteries" for information on repair.

  7.67) Electric scissors

Similar to electric carving knives except for the linkage to the blades.
All other comments apply.

  7.68) Portable and stationary food mixers

These consist of a universal motor which usually features a continuously
variable speed control or a selection of 3 to 5 speeds, a gearbox to transfer
power to the counter-rotating beaters, and a power switch (which may be
part of the speed control).

Sluggish operation may be due to cookie dough embedded in the gearing.  Fine
particles of flour often find their way into the gears - clean and lubricate.
There may be a specific relationship that needs to be maintained between
the two main beater gears - don't mess it up if you need to disassemble and
remove these gears or else the beaters may not lock in without hitting

The speed control may be a (1) selector switch, (2) mechanical control
on the motor itself, or (3) totally electronic.  Parts may be replaceable
although, for portables at least, a new mixer may make more sense.

For sluggish operation (non-mechanical), sparking, burnt smells, etc.,
see the section: "Problems with universal motors".

  7.69) Food processors

A powerful universal motor is coupled to interchangeable cutters of various
types.  In most respects, food processors are similar to any other universal
motor driven appliance with one exception: There will be a safety interlock
switch to prevent operation unless the cover is on properly and secured.  This
switch may go bad or its mechanical position adjustment may shift over time
resulting in difficulty in engaging power - or a totally dead unit.

As usual, cord and plug problems, bad bearings, burnt motor windings,
and broken parts are all possibilities.

  7.70) Steam and dry irons

Most modern irons (does anyone really use these anymore?) can be used
dry or with steam.

An iron consists of a sole plate with an integrated set of heating coils.

Steam irons will have a series of holes drilled in this plate along with
a steam chamber where a small amount of water is boiled to create steam.
A steam iron can be used dry by simply not filling its reservoir with water.
Those with a spray or 'shot of steam' feature provide a bypass to allow
hot water or steam to be applied directly to the article being ironed.

Over time, especially with hard water, mineral buildups will occur in the
various passages.  If these become thick enough, problems may develop.
In addition, mineral particles can flake off and be deposited on the

A thermostat with a heat adjustment usually at the top front of the
handle regulates the heating element.  This is usually a simple bimetal
type but access to the mechanism is often difficult.

Where an iron refuses to heat, check the cord, test the heating element
for continuity with your ohmmeter, and verify that the thermostat is

An iron that heats but where the steam or spray features are missing,
weak, or erratic, probably has clogged passages.  There are products
available to clear these.

Newer irons have electronic timeout controllers to shut the iron off
automatically if not used for certain amount of time as a safety feature.
Failure of these is not likely and beyond the scope of this manual in
any case.

When reassembling an iron, take particular care to avoid pinched or shorted
wires as the case is metal and there is water involved - thus a potential
shock hazard.

  7.71) Toasters

In addition to a fine heating element, there is a controller to determine
the length of time that the bread (or whatever) is heated.  A solenoid
or bimetal trip mechanism is used to pop the bread up (but hopefully not
totally out) of the toaster then it is 'done' and turn off the heating
element at the same time.

Since most of these are so inexpensive, anything more serious than a
broken wire or plug is probably not worth repairing.  The heating
element may develop a broken spot - particularly if something like a
fork is carelessly used to fish out an English muffin, for example.
(At least unplug it if you try this stunt - the parts may be electrically
live, your fork is metal, you are touching it!).  They may just go bad
on their own as well.

Being a high current appliance, the switch contacts take a beating
and may deteriorate or melt down.  The constant heat may weaken various
springs in either the switch contact or pop-up mechanism as well.
Sometimes, some careful 'adjustment' will help.

Controllers may be thermal, timer based, or totally electronic.  Except
for obvious problems like a bent bimetal element, repair is probably not
worth it other then as a challenge.

  7.72) Automatic toaster will not drop bread

If it really is old, then your problem is almost certainly mechanical -
a spring sprung or gummed up burnt raisin bread.  You will have to do
a little investigative research meaning: take the thing apart!  Try to
determine what the bread does to cause the support to drop down. It is
possible that putting the bread in is supposed to trip a microswitch which
activates a solenoid, and the switch or solenoid is now defective - bad
contacts or broken wires, bad coil in the solenoid, or grime.

The following applies directly to several Sunbeam models (and no doubt
to many others as well).

(From: John Riley (jriley@calweb.com)).

I will assume that the  toaster is either a model ATW or possibly an 
older model 20 or the like.

When you drop the bread in the toaster it trips a lever that is attached 
to the bread rack.  This lever pushes in on the contacts inside of the 
thermostat (color control switch) which actually turns the toaster on.
In "most cases" adjusting the screw on the bottom of the toaster will do 
the trick.  The proper adjustment is to adjust the carriage tension so 
that the bread rack in the side where it marked for a single slice of 
bread comes just to the uppermost limit of its travel.  Any more is 

If you have adjusted it as mentioned above and it still won't go down, 
there is one more thing you can try.  Take the toaster a sort of BUMP it 
down onto the table rather firmly.  Sometimes a piece of crumb will get 
in between the thermostat contacts.  A couple of good "bumps" on the 
table will usually dislodge the particle.

If all of the above doesn't work, and you know the cord isn't bad, them 
you may very well have a thermostat that has gone south.  They are still 
available for replacement on most models.  Suggest you check with your 
local SUNBEAM AUTHORIZED SERVICE for price and availability.

  7.73) Toaster oven (broilers)

I really liked the old original style GE toaster oven.  It was very versatile
and convenient for baking and toasting.  The newer types seem to have lost
some of these qualities.  The pop open door and oven tray have apparently
not been retained in any modern models that I am aware of.

Modern toaster oven (broilers) use Calrod style elements - usually two
above and two below the food rack.  Depending on mode, either just the
top (top brown/broil), just the bottom (oven), or both sets (toast) will
be energized.  Each pair may be wired in series meaning that a failure
of one will result in both of the pair being dead.  Very old units may
use a coiled NiChrome element inside a quartz tube.

Thermostats are usually of the bimetal strip variety with an adjustment
knob.  A cam or two on the shaft may also control main power and select
the broil function in the extreme clockwise position.

There may be a mode switch (bake-off-broil) which may develop bad contacts
or may fuse into one position if it overheats.  These are often standard
types and easily replaceable.  Just label where each wire goes on the
switch before removing it to take to an appliance repair parts store.

Newer models may use an electronic timer for the toast function at least.
I assume it is not much more than something like an IC timer (555) operating
the trip solenoid.  However, I have not had to deal with a broken one as

Testing is relatively straightforward.  Check the heating elements, thermostat,
mode switch,, cord, and plug.  While replacements for heating elements and
thermostats are often available, removing the old one and wiring the new one
may not be straightforward - rivets may be used for fastening and welds
for the wire connections.  You will have to drill the rivets with an electric
drill and replace them with nuts, bolts, and lockwashers.  Crimp splices
or nuts and bolts can be used for the wiring.  Take extra care in reassembly
to avoid any bare wires touching the metal cabinet or other parts as well as
insulation being cut by sharp sheetmetal parts.  The high temperature fiberglas
or asbestos insulation is not very robust.  In the end, it may not be
worth it with full featured toaster oven/broilers going for $20-30 on sale.

  7.74) Convection oven noise

Unlike a regular (non-microwave) oven, convection ovens are not totally
silent.  There is a small fan used to circulate the hot air (thus the
name: convection oven).  Depending on the oven's design and age, these
fans may be anywhere from nearly silent to objectionably noisy.

If you notice an increase in motor noise (whining or squealing, grinding,
knocking) then the motor and fan should be inspected and parts replaced
if necessary.  Sudden failure is unlikely but if it were to happen - seized
bearings, for example - an overtemperature thermal protector should shut
down the heating element or entire oven.  Some of these may not be self
resetting (thermal fuse).

  7.75) Hot plates, waffle irons, broilers, deep friers, rice and slow cookers, woks

These are all just a single or dual heating element, thermal protector
(not all will have one), and an adjustable (usually) thermostat.  As usual,
check the cord and plug first, and then each of the other parts with an

Where a NiChrome coil type heating element is used, a break will be obvious.
If it is very near one end, then removing the short section and connecting the
remainder directly to the terminal will probably be fine.  See the section:
"Repair of broken heating elements".

For appliances like waffle irons, burger makers, and similar types with
two hinged parts, a broken wire in or at the hinge is very common.

Note that since these operate at high temperatures, special fiberglass (it
used to be asbestos) insulated wiring is used.  Replace with similar types.
Take extra care in reassembly to avoid shorted wires and minimize the handling
and movement of the asbestos or fiberglas insulated high temperature wiring.

  7.76) Popcorn poppers (oil type)

An Oil popper is basically an electric frying pan with a built-in stirrer and
cover.  The internal parts are accessed from the bottom: Heating coil,
thermostat and thermal protector, and small gear-motor similar to that used
in a clock or timer.  Take care to note the orientation of the motor when
removing and to not damage any seals (you don't want oil seeping down under!).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

If the stirrer doesn't turn, a gummed up motor or stirrer shaft (since these
are only used occasionally) may be the problem.  See the chapter: "Motors 101".

  7.77) Popcorn poppers (air type)

Air poppers combine a heating element and blower to heat corn kernels without
the need for any unhealthy oil.  Of course, you probably then drown the popcorn
in butter and salt, huh?  Admit it! :-).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

The motor is probably a small PM DC type and there will then be a set of
diodes or a bridge rectifier to turn the AC into DC.  Check these and for
bad bearings, gummed up lubrication, or other mechanical problems if the
motor does not work or is sluggish.  See the chapter: "Motors 101".

  7.78) Sewing machines

Moth mechanical and electrical problems are possible.  (Note: we are not
going to deal with fancy computerized equipment as this is probably better
left to a professional except for the more obvious problems like a bad
cord or plug.)

I have a 1903 Singer foot-pumped sewing machine which we have since electrified
and still runs fine.  A couple of drops of sewing machine or electric motor
oil every so often is all that is needed.  They were really built well back

Although the appearance of the internal mechanism may appear intimidating
at first, there really is not that much to it - a large pulley drives a
shaft that (probably) runs the length of the machine.  A few gears and
cams operate the above (needle and thread) and below (feet and bobbin)
deck mechanisms.  Under normal conditions, these should be pretty robust.
(Getting the adjustments right may be another story - refer to your users
manual).  Sometimes if neglected, the oil may seriously gum up and require
the sparing use of a degreaser to loosen it up and remove before relubing.

If the motor spins but does not turn the main large pulley, the belt is
likely loose or worn.  The motor will generally be mounted on a bracket
which will permit adjustment of the belt tension.  The belt should be tight
but some deflection should still occur if you press it gently in the middle.

If the motor hums but nothing turns, confirm that the belt is not too tight
and/or that the main mechanisms isn't seized or overly stiff - if so, it
will need to be cleaned and lubrication (possibly requiring partial

The electric motor is normally a small universal type on a variable speed
foot pedal (see the section: "Wiring a sewing machine speed control").

If the motor does not work at all, bypass the foot pedal control to confirm
that it is a motor problem (it is often possibly to just plug the motor
directly into the AC outlet).  Confirm that its shaft spins freely.  All
normal motor problems apply - bad wiring, worn brushes, open or shorted
windings, dirty commutator.  See the section: "Problems with universal motors".

  7.79) Wiring a sewing machine speed control

This assumes a basic sewing machine (nothing computer controlled) with
a normal universal series wound motor (115 VAC).

The common foot pedals are simply wirewound rheostats (variable resistors)
which have an 'off' position when the pedal is released.  They are simply
wired in series with the universal motor of the sewing machine (but not
the light) and can be left plugged in all the time (though my general
recommendation as with other appliances is to unplug when not in use.

While not as effective as a thyristor type speed controller, these simple
foot pedals are perfectly adequate for a sewing machine.  There are also
fancier speed controls and using a standard light dimmer might work in some
cases.  However, there are two problems that may prevent this: the sewing
machine motor is a very light load and it is a motor, which is not the same
as a light bulb - it has inductance.  The dimmer may not work, may get stuck
at full speed, or may burn out.

  7.80) Shavers

A variety of types of drive mechanisms are used in electric shavers:

1. Vibrator (AC only) - these (used by Remington among others) consist of
   a moving armature in proximity to the pole pieces of an AC electromagnet.
   The mass and spring are designed so that at the power line frequency, the
   armature vibrates quite strongly and is linked to a set of blades that
   move back and forth beneath the grille.

   If dead, check for continuity of the plug, cord, switch, and coil.  IF
   sluggish, clean thoroughly - hair dust is not a good lubricant.  Sliding
   parts probably do not require lubrication but a drop of light oil should
   be used on any rotating bearing points.

   Note that since a resonance is involved, these types of shavers may not
   work well or at all on foreign power - 50 Hz instead of 60 Hz or vice
   versa - even if the voltage is compatible.

2. Universal motor (AC or DC) - very small versions of the common universal
   motors found in other appliances.  A gear train and linkage convert the
   rotary motion to reciprocating motion for shavers with straight blades or
   to multiple rotary motion for rotary blade shavers.  These may suffer
   from all of the afflictions of universal motors; bad cords, wires, and
   switches; and gummed up, clogged, or worn mechanical parts.  Also see
   the sections on the appropriate type of motor.  Take care when probing
   or disassembling these motors - the wire is very fine any may be easily
   damaged - I ruined an armature of a motor of this type by poking where
   I should not have when it was running - ripped all the fine wires from
   the commutator right off.

3. DC PM motor - often used in rechargeable shavers running of 2 or 3 NiCd
   cells.  These may suffer from battery problems as well as motor and
   mechanical problems.  One common type is the Norelco (and clone) rotary
   shaver.  See the chapters on Batteries and AC Adapters as well as the
   sections on "Small permanent magnet DC motors".

   A shaver that runs sluggishly may have a dead NiCd cell - put it on
   charge for the recommended time and then test each cell - you should
   measure at least 1.2 V.  If a NiCd cell reads 0, it is shorted and
   should be replaced (though the usual recommendation is to replace all
   cells at the same time to avoid problems in the future).

   Note that in terms of rechargeable battery life, shavers are just about
   optimal as the battery is used until it is nearly drained and then 
   immediately put on charge.  The theoretical 500 to 1000 cycle NiCd life
   is usually achieved in shaver applications.

  7.81) Electric toothbrushes

These are basically similar to any other small battery operated appliance or
tool such as a screwdriver or drill.  The permanent magnet motor runs off of
rechargeable NiCd batteries and cause the bristles or whatever to oscillate,
rotate, or vibrate.  Interchangeable 'brush' units allow each member of the
family to have their own.

Problems can occur in the following areas:

* Motor, battery pack, connections, on/off switch - as with any other similar

* Power train - gummed up lubrication, broken, or other mechanical problems.

* Charging station or circuitry - the fault may be with the base unit or
  circuitry associated with the battery pack.  See the section: "Braun electric
  toothbrush repair", below.

Since these must operate in a less than ideal environment (humid or actual
waterlogged!), contamination and corrosion is quite possible if the case is
not totally sealed.  Some of the switched may be of the magnetic reed type so
that there don't need to be any actual breaks in the exterior plastic housing.

Of course, getting inside may prove quite a challenge:

(From: Jeff & Sandy Hutchinson (sandy2@flatoday.infi.net)).

It's darned near impossible to replace the batteries on the Interplak
toothbrush without destroying the recharging circuit.  The base of the hand
unit has a little pickup coil in it, and when you unscrew the cap to get at
the batteries, you break the connections to the pickup coil.  Best to do an
exchange with the factory.

  7.82) Braun electric toothbrush repair

(From: David DiGiacomo (dd@Adobe.com)).

This Braun electric toothbrush (original model) would turn itself on and keep
running until its batteries were discharged.

The toothbrush can be disassembled by pulling the base off with slip joint
pliers (do not pull too hard because there is only about 1" of slack in
the charging coil wires).  With the base off, the mechanism slides out of
the case.

There is a simple charging circuit, charging LED, 2 NiCd cells, and a reed
switch driving the base of an NPN transistor.  The transistor collector
drives the motor.

I charged the battery, but the problem of the motor running with the reed
switch open didn't recur until I held my finger on the transistor for
about 10 seconds seconds.  Grounding the transistor base turned it off
again, and I could repeat this cycle.  Since there wasn't anything else to
go wrong I decided to replace the transistor.  I couldn't read the
marking, but it's in a SOT89 package and the motor current is 400-700 mA so
it must be something like a BC868.  However, I didn't have any surface
mount or TO92 transistors that could handle the current, so I used a
2SD882 (small power tab package), which I was able to squeeze into some
extra space in the center of the charging coil.

  7.83) Hand massagers

These are simply motors with an off-axis (eccentric) weight or electromagnetic
vibrators.  If the unit appears dead, check the plug, cord, on/off switch,
internal wiring, and motor for continuity.  Confirm that the mechanical parts
turn or move freely.

Some have built in infra-red heat which may just be a set of small light
bulbs run at low voltage to provide mostly heat and little light (a filter
may screen out most of the light as well).  Obviously, individual light
bulbs can go bad - if they are wired in series, this will render all of
them inert.

At least one brand - Conair - has had problems with bad bearings.  Actually,
poorly designed sleeve bearings which fail due to the eccentric load.  If you
have one of these and it becomes noisy and/or fails, Conair will repair
(actually replace) it for $5 if you complain in writing and send it back to
them.  They would like a sales receipt but this apparently is not essential.

  7.84) Hair dryers and blow dryers

A heating element - usually of the NiChrome coil variety - is combined with
a multispeed centrifugal blower.

First determine if the problem is with the heat, air, or both.

For heat problems, check the element for breaks, the thermal protector
or overtemperature thermostat (usually mounted in the air discharge), the
connections to the selector switch, and associated wiring.

For air problems where the element glows but the fan does not run, check the
fan motor/bearings, connections to selector switch, and associated wiring.
Confirm that the blower wheel turns freely and is firmly attached to the
motor shaft.  Check for anything that may be blocking free rotation if the
blower wheel does not turn freely.  The motor may be of the induction,
universal, or PM DC type.  For the last of these, a diode will be present
to convert the AC to DC and this might have failed.  See the appropriate
section for problems with the type of motor you have.

  7.85) Curling irons

These are just a sealed heating element, switch, and thermal protector
(probably).  Check for bad connections or a bad cord or plug if there is
not heat.  A failed thermal protector may mean other problems.  While
these are heating appliances, the power is small so failures due to
high current usually do not occur.

  7.86) VCR cassette rewinders

Cassette rewinders typically consist of a low voltage motor powered from
a built in transformer or wall adapter, a belt, a couple of reels, and some
means of stopping the motor and popping the lid when the tape is fully

Note that some designs are very hard on cassettes - yanking at the tape
since only increased tension is used to detect when the tape is at the end.
These may eventually stretch the tape or rip it from the reel.  I don't
really care much for the use of tape rewinders as normal use of rewind and
fast forward is not a major cause of VCR problems.  Sluggish or aborted
REW and FF may simply indicate an impending failure of the idler tire or
idler clutch which should be addressed before the VCR gets really hungry
and eats your most valuable and irreplaceable tape.

Problems with tape rewinders are usually related to a broken or stretched
belt or other broken parts.  These units are built about as cheaply as
possible so failures should not be at all surprising.  The drive motor can
suffer from any of the afflictions of similar inexpensive permanent magnet
motors found in consumer electronic equipment.  See the section: "Small
permanent magnet DC motors".  A broken belt is very common since increased
belt (and tape) tension is used to switch the unit off (hopefully).  Parts can
pop off of their mountings.  Flimsy plastic parts can break.

Opening the case is usually the biggest challenge - screws or snaps may
be used.  Test the motor and its power supply, inspect for broken or
dislocated parts, test the power switch, check and replace the belt if
needed.  That is about it.

  7.87) Vacuum cleaners, electric brooms. and line powered hand vacs

Despite all the hype surrounding vacuum cleaner sales, there isn't much
difference in the basic principles of operation between a $50 and $1,500
model - and the cheaper one may actually work better.

A vacuum cleaner consists of:

1. A cordset - broken wires or damaged plugs are probably the number one
   problem with vacuums as they tend to be dragged around by their tails!
   Therefore, in the case of an apparently dead machine, check this first -
   even just squeezing and bending the wire may produce an instant of
   operation - enough to verify the cause of the problem.

2. A power switch - this may be a simple on/off toggle which can be tested
   with a continuity checker or ohmmeter.  However, fancy machines with
   powered attachments may have interlocks or switches on the attachments
   that can also fail.  Where multiple attachment options are present, do
   your initial troubleshooting with the minimal set as this will eliminate
   potential sources of additional interlock or switch complications.  With
   'microprocessor' or 'computer' controlled vacuum cleaners, the most likely
   problems are not the electronics.

3. A high speed universal motor attached to a centrifugal blower wheel.
   As with any universal motor, a variety of problems are possible: dirt
   (especially with a vacuum cleaner!), lubrication, brushes (carbon),
   open or shorted windings, or bad connections.  See the section:
   "Problems with universal motors".

4. A belt driven carpet brush (uprights).  The most common mechanical problem
   with these is a broken rubber belt.  (One person who shall remain nameless,
   mistook the end of the broken belt for the tail of a mouse and promptly
   went into hysterics!).  Replacements for these belts are readily available.

5. Power nozzles and other powered attachments.  Some of these are an attempt
   to give canister type vacuum cleaners the power of an upright with its
   directly powered carpet brush.  Generally, these include a much smaller
   motor dedicated to rotating a brush.  Electrical connections are either
   made automatically when the attachment is inserted or on a separate
   cable.  Bad connections, broken belt, or a bad motor are always

6. A bag to collect dirt.  Vacuum cleaners usually do a poor job of dust
   control despite what the vacuum cleaner companies would have you believe.
   Claims with respect to allergies and other medical conditions are generally
   without any merit unless the machine is specifically designed (and probably
   very expensive) with these conditions in mind.  If the vacuum runs but with
   poor suction, first try replacing the bag.

  7.88) Vacuum cleaner mechanical problems

1. Poor suction - check the dirt bag and replace if more than half full.
   Check for obstructions - wads of dirt, carpet fibers, newspapers, paper
   towels, etc.

2. Poor pickup on floors - broken or worn carpet brush belt.  There should
   be some resistance when turning the carpet brush by hand as you are also
   rotating the main motor shaft.  If there is none, the belt has broken
   and fallen off.  Replacements are readily available.  Take the old one
   and the model number of the vacuum to the store with you as many models
   use somewhat similar but not identical belts and they are generally not
   interchangeable.  To replace the belt on most uprights only requires the
   popping of a couple of retainers and then removing one end of the carpet
   brush to slip the new belt on.

3. Vacuum blows instead of sucks - first confirm that the hose is connected
   to the proper port - some vacuums have easily confused suction and blow
   connections.  Next, check for internal obstructions such as wads of dirt,
   balls of newspaper, or other items that may have been sucked into the
   machine.  Note that it is very unlikely - bordering on the impossible -
   for the motor to have failed in such a way as to be turning in the wrong
   direction (as you might suspect).  Furthermore, even if it did, due to
   the design of the centrifugal blower, it would still suck and not blow.

4. Broken parts - replacements are available for most popular brands from
   appliance repair parts distributors and vacuum/sewing machine repair

  7.89) Vacuum cleaner electrical problems

1. Bad cord or plug - number one electrical problem due to the abuse that
   these endure.  Vacuum cleaners are often dragged around and even up and
   down stairs by their tails.  Not surprisingly, the wires inside eventually
   break.  Test with a continuity checker or ohmmeter.  Squeezing or bending
   the cord at the plug or vacuum end may permit a momentary spurt of
   operation (do this with it plugged in and turned on) to confirm this

2. Bad power switch - unplug the vacuum and test with a continuity checker
   or ohmmeter.  If jiggling the switch results in erratic operation, a new
   one will be required as well.

3. Bad interlocks or sensors - some high tech vacuum cleaners have air flow
   and bag filled sensors which may go bad or get bent or damaged.  Some
   of these can be tested easily with an ohmmeter but the newest computer
   controlled vacuum cleaners may be more appropriate to be repaired by a
   computer technician!

4. Bad motor - not as common as one might thing.  However, worn carbon
   brushes or dirt wedged in and preventing proper contact is possible.
   See the section: "Problems with universal motors".

5. Bad internal wiring - not likely but always a possibility.

  7.90) Vacuum cleaner hose damage

"We have been quoted a price of $100 to replace the hose on our Panasonic
 (Mc-9537) vacuum cleaner. It has a rip in it; next to the plastic housing 
 where the metal tubing starts.  Does anyone know if there is a more 
 economical way to solve this problem?"

I have always been able to remove the bad section and then graft what is
left back on to the connector.  Without seeing your vacuum, there is no way
to provide specific instructions but that is what creativity is for! :-)
It might take some screws, tape, sealer, etc.

$100 for a plastic hose is obviously one approach manufacturers have of
getting you to buy a new vacuum - most likely from some other manufacturer!

Note: Some vacuum cleaners with power nozzles use the coiled springs of the
hose as the electrical conductors for the power nozzle.  If you end up cutting
the hose to remove a bad section, you will render the power nozzle useless.

  7.91) High tech vacuum cleaners?

Excerpt from a recent NASA Tech Brief:

"The Kirby Company of Cleveland, OH is working to apply NASA technology to
 its line of vacuum cleaners.  Kirby is researching advanced operational
 concepts such as particle flow behavior and vibration, which are critical
 to vacuum cleaner performance.  Nozzle tests using what is called Stereo
 Imaging Velocity will allow researchers to accurately characterize fluid
 and air experiments.  Kirby is also using holography equipment to study
 vibration modes of jet engine fans."

I suppose there will be degree-credit university courses in the operation
of these space age vacuums as well! --- sam

  7.92) Dustbusters(tm) and other battery powered hand vacs

These relatively low suction battery powered hand vacuums have caught on
due to their convenience - certainly not their stellar cleaning ability!

A NiCd battery pack powers a small DC permanent magnet motor and centrifugal
blower.  A simple momentary pushbutton power switch provides convenient
on/off control.

Aside from obvious dirt or liquid getting inside, the most common problems
occur with respect to the battery pack.  If left unused and unplugged for
a long time, individual NiCd cells may fail shorted and not take or hold
a charge when the adapter is not plugged back into the wall socket.  Sluggish
operation is often due to a single NiCd cell failing in this way.

See the appropriate sections on "Batteries" and "Motors" for more information.

  7.93) Dustbusters left on continuous charge and battery problems

The low current trickle charger supplied with these battery operated hand-vacs
allow Dustbusters and similar products to be be left on continuous charge so
long as they are then not allowed to self discharge totally (left on a shelf
unplugged for a long time).  Older ones, in particular, may develop shorted
cells if allowed to totally discharge.  I have one which I picked up at a
garage sale where I had to zap cells to clear a shorts.  However, it has been
fine for several years now being on continuous charge - only removed when used.

While replacing only selected cells in any battery operated appliance is
generally not recommended for best reliability, it will almost certainly
be much cheaper to find another identical unit at a garage sale and make
one good unit out of the batteries that will still hold a charge.  It is
better to replace them all but this would cost you as much as a new

The NiCd cells are soldered in (at least in all those I have seen) so
replacement is not as easy as changing the batteries in a flashlight but
it can be done.  If swapping cells in from another similar unit, cut the
solder tabs halfway between the cells and then solder the tabs rather than
to the cells themselves if at all possible.  Don't mess up the polarities!

In the case of genuine Dustbusters, where a new battery is needed and you
don't have a source of transplant organs, it may be better to buy the
replacement cells directly from Black and Decker. They don't gouge you on NiCd
replacements.  B&D is actually cheaper than Radio Shack, you know they are the
correct size and capacity, and the cells come with tabs ready to install.
They'll even take your old NiCds for proper re-cycling.

  7.94) Floor polishers

A relatively large universal motor powers a set of counter-rotating
padded wheels.  Only electrical parts to fail: plug, cord, power switch,
motor.  Gears, shafts, and other mechanical parts may break.

  7.95) Heating pads

Heating pads are simply a very fine wire heating element covered in thick
insulation and then sealed inside a waterproof flexible plastic cover.
Internal thermostats prevent overheating and regulate the temperature.
The hand control usually provides 3 heat settings by switching in different
sections of the heating element and/or just selecting which thermostat is used.

There are no serviceable parts inside the sealed cover - forget it as any
repair would represent a safety hazard.  The control unit may develop bad
or worn switches but even this is somewhat unlikely.  It is possible to
disassemble the control to check for these.  You may find a resistor or diode
in the control - check these also.  With the control open, test the wiring to
the pad itself for low resistance (a few hundred ohms) between any pair of
wires).  If these test open, it is time for a new heating pad.  Otherwise,
check the plug, cord, and control switches.

Extended operationg especially at HIGH, or with no way for the heat to escape,
may accelerate deterioration inside the sealed rubber cover.  One-time thermal
fuses may blow as well resulting in a dead heating pad.  One interesting note:
Despite being very well sealed, my post mortems on broken heating pads have
shown one possible failure to be caused by corrosion of the internal wiring
connections after many years of use.

  7.96) Electric blankets

As with heating pads, the only serviceable parts are the controller and
cordset.  The blanket itself is effectively sealed against any repair
so that any damage that might impact safety will necessitate replacement.

Older style controllers used a bimetal thermostat which actually sensed
air temperature, not under-cover conditions.  This, it turns out, is a
decent measurement and does a reasonable job of maintaining a comfortable
heat setting.  Such controllers produced those annoying clicks every couple
of minutes as the thermostat cycled.  Problems with the plug, cord, power
switch, and thermostat contacts are possible.  The entire controller usually
unplugs and can be replaced as a unit as well.

Newer designs use solid state controls and do away with the switch
contacts - and the noise.  Aside from the plug and cord, troubleshooting
of a faulty or erratic temperature control is beyond the scope of this

  7.97) Humidifiers

There are three common types:

1. Wet pad or drum - a fan blows air across a stationary or rotating
   material which is water soaked.  There can be mechanical problems
   with the fan or drum motor or electrical problems with the plug,
   cord, power switch, or humidistat.

2. Spray - an electrically operated valve controls water sprayed from
   a fine nozzle.  Problems can occur with the solenoid valve (test the
   coil with an ohmmeter), humidistat, or wiring.  The fine orifice may
   get clogged by particles circulating in the water or hard water deposits.
   In cleaning, use only soft materials like pointy bits of wood or plastic
   to avoid enlarging the hole in the nozzle.

3. Ultrasonic - a high frequency power oscillator drives a piezo electric
   'nebulizer' which (with the aid of a small fan) literally throws fine
   droplets of water out into the room.  Problems with the actual ultrasonic
   circuitry is beyond the scope of this manual but other common failures
   can be dealt with like plug, cord, fan motor, control switches, wiring,
   etc.  However, if everything appears to working but there is no mist
   from the output port, it is likely that the ultrasonic circuitry has
   failed.  See the section: "Ultrasonic
   humidifiers" for more details.

  7.98) Ultrasonic humidifiers

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

The components of the typical $45 unit are:

* Piezo transducer + electronics (usually in a metal cage - we are talking
  line current here - not safe!).

* Small blower/fan.

* Float-switch.

* Water tank.

The piezo transducer sets up a standing wave on the surface of the water pool.
The level is sensed with a float-switch to ensure no dry-running (kills the
piezo) and the blower/fan propels the tiny water droplets out of the cavity.
A few manufacturers are nice enough to include a silly air filter to keep any
major dust out of the 'output' - do clean/check that once in a while.

Common problems:

* Low output:

  - Minerals from water deposited on surface(s) of the water pool - including
    the piezo. This disrupts/changes the resonance/output of the piezo - and
    you see the effect.

  - Clogged air filter - there should be a little 'trap door' somewhere
    on the case with a little grill. Pop it out and wash the filter found
    therein. Replace.

  - Driver of the piezo going down that hill. Time to get another one or
    look for the warranty card if it applies.
CAUTION: Unless you know what you are doing (and have gotten shocked a
few times in your life) DO NOT play with the piezo driver module. Most
run at line voltage with sometimes 100+V on heatsinks - which are live.

* No output:

  - Dead piezo driver - get a new unit unless under warranty.

  - Dead wire or float-switch or humidity switch or 'volume'... that 
    should be easy - use an ohmmeter and look for shorts/opens/resistance.

  - Dead fan - should still have mist - just none of it getting out.

  - No power in the outlet you're using ;-)

Note: piezo's in general are driven with voltage, as opposed to current. This
explains why you can expect high voltages - even in otherwise low-voltage
circuits. Case in point: the Polaroid ultrasonic sonar modules.

  7.99) Ultrasonic waterfalls?

I don't suppose you are likely to encounter these but if you do, servicing
procedures will be similar to those described in the section: "Ultrasonic humidifiers".

(From: Roger Vaught (vaurw@onramp.net)).

At a local shop they sell small water fall displays made from limestone in a
marble catch basin.  These are made in China. They use a small water pump for
the flow.  

When I first saw one I thought the store had placed dry ice in the cavity
where the water emerged as there was a constant stream of cloud flowing from
it.  Very impressive. It turns out they use the ultrasonic piezo gizmo to make
the cloud.  The driver is a small 3 X 5 X 3 inch box with a control knob on
top.  If you look into the cavity you can see the piezo plate and a small red
LED.  The water periodically erupts into vapor.  I haven't been able to get a
close look at the driver so I can't tell where it is made or if there is a
product name or manufacturer.  They will sell that part of it for $150! 

  7.100) Ultrasonic cleaners

Ultrasonic cleaning is a means of removing dirt and surface contamination from
intricate and/or delicate parts using powerful high frequency sound waves in
a liquid (water/detergent/solvent) bath.

An ultrasonic cleaner contains a power oscillator driving a large piezoelectric
transducer under the cleaning tank.  Depending on capacity, these can be quite

A typical circuit is shown below.  This is from a Branson Model 41-4000 which
is typical of a small consumer grade unit.

               R1        D1
 H o------/\/\-------|>|----------+
         1, 1/2 W  EDA456         |
               C1         D2      |
          |  .1 uF   |  EDA456    |  2  
          |  200 V   |      +-----+---+ T1      +---+------->>------+
          |    R2    |     _|_ C2      )||  o 4 |   |               |
          +---/\/\---+     --- .8 uF D )|| +----+   |               |
          |   22K          _|_ 200 V   )||(         +               |
          |   1 W           -      1 o )||(          )||           _|_
          +-----------------+---------+ ||( O        )|| L1        _x_ PT1
          |           R3    |        7  ||(          )||            |
          |      +---/\/\---+   +-----+ ||( 5       +               |
         C \|    | 10K, 1 W     |    F )|| +---+    |               |
       Q1   |--+-+--------------+  6 o )||     |    |               |
         E /|  |  D3     R4       +---+        +----+------->>------+
          |    +--|<|---/\/\--+  _|_
          |           47, 1 W |  ---       Input: 115 VAC, 50/60 Hz
          |                   |   |        Output: 460 VAC, pulsed 80 KHz
 N o------+-------------------+---+

The power transistor (Q1) and its associated components form an self excited
driver for the piezo-transducer (PT1).  I do not have specs on Q1 but based on
the circuit, it probably has a Vceo rating of at least 500 V and power rating
of at least 50 W.

Two windings on the transformer (T1, which is wound on a toroidal ferrite
core) provide drive (D) and feedback (F) respectively.  L1 along with the
inherent capacitance of PT1 tunes the output circuit for maximum amplitude.

The output of this (and similar units) are bursts of high frequency (10s to
100s of KHz) acoustic waves at a 60 Hz repetition rate.  The characteristic
sound these ultrasonic cleaners make during operation is due to the effects
of the bursts occuring at 60 Hz since you cannot actually hear the ultrasonic
frequencies they use.

The frequency of the ultrasound is approximately 80 KHz for this unit with a
maximum amplitude of about 460 VAC RMS (1,300 V p-p) for a 115 VAC input.

WARNING: Do not run the device with an empty tank since it expects to have
a proper load.  Do not touch the bottom of the tank and avoid putting your
paws into the cleaning solution while the power is on.  I don't know what,
if any, long term effects there may be but it isn't worth taking chances.
The effects definitely feel strange.

Where the device doesn't oscillate (it appears as dead as a door-nail), first
check for obvious failures such as bad connections and cracked, scorched, or
obliterated parts.

To get inside probably requires removing the bottom cover (after pulling the
plug and disposing of the cleaning solution!).

CAUTION: Confirm that all large capacitors are discharged before touching
anything inside!

The semiconductors (Q1, D1, D2, D3) can be tested for shorts with a multimeter
(see the document: "Basic Testing of Semiconductor Devices".

The transformer (T1) or inductor (L1) could have internal short circuits
preventing proper operation and/or blowing other parts due to excessive load
but this isn't kind of failure likely as you might think.  However, where all
the other parts test good but the cleaning action appears weak without any
overheating, a L1 could be defective (open or other bad connections) detuning
the output circuit.

  7.101) Dehumidifiers

Electric dehumidifiers use a refrigeration system to cool a set of coils
which condenses water vapor.  The heat is then returned to the air and
it is returned back to the room.  On the surface, this seems like an
incredible waste of energy - cooling the air and heating it back up -
but it is very effective at removing moisture.  A typical large dehumidifier
will condense something like 30 pints in 24 hours - which, unless you have
it located over a drain - then needs to be dumped by hand.

There is supposed to be a cutoff (float) switch to stop the dehumidifier
when the container is full.  Hopefully, it works (and you didn't neglect
to install it when the unit was new!)

Common problems with these units are often related to the fan, humidistat,
or just plain dirt - which tends to collect on the cooling coils.  The
sealed refrigeration system is generally quite reliable and will never need

An annual cleaning of the coils with a soft brush and a damp cloth is a good
idea.  If the fan has lubrication holes, a couple of drops (but no more) of
electric motor oil should be added at the same time.

The fan uses an induction motor - shaded pole probably - and may require
cleaning and lubrication.  See the section: "Problems with induction motors".

The humidistat may develop dirty or worn contacts or the humidity sensing
material - sort of like a hot dog wrapper - may break.  If you don't hear
a click while rotating the control through its entire range, this may have
happened.  If you hear the click - and the dehumidifier is plugged into
a live outlet - but nothing happens, then there is probably a problem in
the wiring.  If just the fan turns on but not the compressor, (and you have
waited at least 5 minutes for the internal pressures to equalize after
stopping the unit) then there may be a problem with the compressor or its
starting relay (especially if the lights dim indicating a high current).

A very low line voltage condition could also prevent a refrigeration system
from starting or result in overheating and cycling.  A sluggish slow rotating
or seized fan, or excessive dirt buildup may also lead to overheating and
short cycling.

A unit that ices up may simply be running when it is too cold (and you don't
really need it anyway).  Dehumidifiers may include sensors to detect ice
buildup and/or shut off if the temperature drops below about 60 degrees F.

  7.102) Garbage disposals

A garbage disposal is just an AC induction motor driving a set of centrifugal
hammers (they use to use sharp cutters but these were even more dangerous).
The cutters throw the food against an outer ring with relatively sharp slots
which break up the food into particles that can be handled (hopefully) by
the waste system.  However, always use generous amounts of cold water (which
helps to cool the motor as well) and let it run for a while after there is
nothing left in the disposal and it has quieted down.  This will assure a
trouble free drain.  Otherwise, you may be inviting your friendly plumber
over for a visit!

Common problems with garbage disposals relate to three areas:

* Something stuck in grinding chamber - disposal hums or trips internal
  protector (red button) or main fuse or circuit breaker.  Unplug disposal!
  Then use the wrench (or appropriate size hex wrench) that came with the
  disposal to work rotor back and forth from bottom.  If there is no hole
  for a wrench (or you misplaced yours), try a broom handle from above but
  NEVER put your hand in to try to unjam it (there are still relatively
  sharp parts involved).   With the disposer unplugged, you can carefully
  reach in and feel for any objects that may be stuck or which cannot be
  broken up by the grinding action (like forks, toys, rocks, beef bones,
  etc.) and fish these out.  Once free, restore power (if needed) and/or
  reset red button ((usually underneath the motor housing - you may have
  to wait a couple minutes until it will reset (click and stay in).  Then
  run the unit with full flow of cold water for a couple of minutes to clear
  anything remaining from the grinding chamber and plumbing.

* Motor - although these only run for a few seconds a day, motor problems
  including shorted windings or defective rotors are possible.   Assuming
  rotor turns freely, these may include a hum but no movement, repeated
  blown fuses or tripped circuit breakers, or any burning smells.

* Leaking shaft seal - probably what causes most disposals to ultimately
  fail.  The upper seal develops a slight leak which permits water to enter
  the motor housing damaging the bearing and causing electrical problems.
  Symptoms include seized rotor, excessive noise or vibration,  actual
  water leaking from inside the motor housing, burning smells, etc.

* Power switch (built into batch feed models) - wall switches can go bad
  like any other application.  The built in magnetic or microswitch in a
  batch feed disposal can also fail.  Intermittent or no operation may

* Drain blockage - disposal runs but water doesn't get pumped out of sink
  or backs up.  Use plumber's helper (plunger) or better yet, remove U-trap
  under sink and use a plumber's (steel) snake to clear blockage in the
  waste pipe.  NEVER NEVER use anything caustic!!!  First of all, it will
  not likely work (don't believe those ads!).  More importantly, it will
  leave a dangerous corrosive mess behind for you or the plumber to clean
  up.  The plunger or snake will work unless the blockage is so impacted
  or in a bad location (like a sharp bend) in which case a professional
  will need to be called in any case.

Unless you are the truly die-hard doit-yourselfer, repair of disposals is
probably not a good use of your time.  The ultimate reliability of all
but the most obvious and simple repairs is usually unknown and could be
very short.  However, other than time, there is nothing to be lost by
at least investigating the source of the problem.

  7.103) Garbage disposal pops reset button but nothing blocked

Even if nothing is stuck in it, is the rotor free - not too tight?  If you
have that little wrench that comes with many disposers, you should be able
to turn the rotor relatively easily (I would say about 1 foot-pound of
torque or less if your arm is calibrated).  A tight bearing may be the
result of a shaft seal leak - see the next section: "Garbage disposal seizes

The red reset button is a circuit breaker.  Either the motor is drawing
too much current due to a shorted winding or a tight bearing or the breaker
is faulty.  Without an ammeter, it will be tough to determine which it
is unless the rotor is obviously too tight.

If you have a clamp-on ammeter, the current while the motor is running
should be less than the nameplate value (startup will be higher).  If
it is too high, than there is likely a problem with the motor.  As an
alternate you could try bypassing the circuit breaker with a slow blow
fuse of the same rating as the breaker (it hopefully will be marked) or
a replacement breaker (from another dead garbage disposal!.  If this
allows the disposer to run continuously your original little circuit
breaker is bad.  These should be replaceable.

If the bearings are tight, it is probably not worth fixing unless it is
due to something stuck between the grinding disk and the base.  Attempting
to disassemble the entire unit is likely to result in a leak at the top
bearing though with care, it is possible to do this successfully.

  7.104) Garbage disposal is stuck - hums but does not turn

"I need help.  Our garbage disposal is stuck.  It hums but doesn't turn.  If I
 leave it on for more than a few seconds it trips the circuit breaker on the unit.
 Any tips on how to solve this shy of buying a new unit?  The unit is 7 years old."

"I have an ISE In-Sink-Erator (tm), Badger I model.  I tried turning mine on a
 few minutes ago, the motor started then stopped and now nothing happens when I
 flip the wall switch, not even a click."

Of course, first make sure there is nothing jamming it - use a flashlight
to inspect for bits of bone, peach pits, china, glass, metal, etc.  Even a
tiny piece - pea size - can get stuck between the rotating disk and the
the rotor back and forth using the hex wrench that came with the unit or
a replacement (if your unit is of the type that accepts a wrench from below.
If it is not of this type, use the infamous broom handle from above.)

The internal circuit breaker will trip to protect the motor if the rotor
doesn't turn.  Turn off the wall switch, wait a few minutes for the circuit
breaker and motor to cool, and then press the red reset button underneath
the disposal.  If it does not stay in, then you didn't wait long enough or
the circuit breaker itself is defective.  Then, turn on the water and try
the wall switch again (in-sink switch if it is a batch feed model).

Assuming it is still tight with nothing stuck inside and/or jams repeatedly:

(From: Rob-L (rob-l@superlink.net)).

That's about how long it takes for the nut to rust away on the shredder
disc of Insinkerator/Sears units.  My comments will address ISE/Sears
deluxe models with the stainless disc, for those who might have one.

When the nut/washer rusts away, the disc will wobble and get jammed.  With
the power off, try to rock the disc inside the unit. You might need to
wiggle the motor shaft with a 1/4" hex wrench under the unit.  

If you can free things up, and the disc can be rocked, it's the
nut/washer.  When that goes, so does the gasket, and unfortunately it
requires total disassembly of the grinding chamber to replace the little
gasket, because the disc will not come out otherwise.  And if you don't
replace the gasket, water/gunk will run down the motor shaft and into the
motor. When those units go, you're better off to get a new disposer.  

I think they intentionally use a non-stainless steel nut, because
otherwise the units would last a long time.  Even the replacement nuts
will corrode.  The motor shaft will also corrode, but not as fast as the
nut.  With a stainless shaft and nut/washer, the disposer would give many
more years of service.  And that's why they don't make 'em that way. :)

One part that is worth replacing is the mounting gasket.  It's the part
with the flaps that you feed things through.  It gets cut-up and damaged
by chlorine from sink cleaning or dishwasher discharge. (brittle, rough) 
It's a $4 part, usually available at Home Depot next to the new disposers,
and it slips on in a matter of minutes -- you just disconnect the trap,
then drop the disposer down by undoing the retaining ring.  Swap the
gasket, re-attach things, and your sink drain looks brand new.

  7.105) Garbage disposal seizes repeatedly

A garbage disposal that doesn't have anything stuck in the cutting chamber
but seems to be hard to turn or will work with effort until left alone for
a day or two probably has a bad bearing caused by a leak at the shaft seal.
Of course, water gushing out of the lower part of the disposal (or *any*
amount of water dripping from inside the motor housing) is one indication
that there is a leak!  This also represents a safety hazard so the disposal
should be left unplugged and not be used even if it still runs.

By the time the leak is detected, it is probably too late to save the
disposal as corrosion of the steel shaft, excessive wear of the bronze
bushing, as well as possible electrical damage has already occurred.

Realistically, there is nothing that could have likely been done in any
case.  It is virtually impossible to repack such a bearing in such a way
to assure that a leak will not develop in the near future.

  7.106) Garbage disposal replacement (or upgrade)

My general recommendation is to get the approximately $100 1/2-3/4 Hp Sears (ISE
In-Sinkerator(tm) manufactured) unit when it is on sale (which is about every
week).  These now have at least a 4 year warranty.

If your previous garbage disposal was an ISE In-Sinkerator or Sears, then
replacement is usually a 10 minute job if the under-sink plumbing is in
reasonably good condition (doesn't crumble to dust when you touch it).
If the part that mounts to the sink is not corroded and not leaking, I
just leave it alone.  The only tools required are a screwdriver and wire
strippers (possibly) to move the power cord or cable to the new unit and
a screwdriver or socket driver and a large adjustable wrench or pliers to
unscrew the drain pipe and dishwasher connection (if used).  Complete
instructions should be provided with the replacement unit.

  7.107) Sump pumps and utility pumps

Sump pumps come in two major varieties:

1. Pedestal - a motor on top of a 3 foot or so pole drives an impeller at
   the bottom of its long shaft.  Only the base may be submerged.

   These motors are quite reliable but the bearing can rot/rust/seize at
   the base where it may be under water or at least in a humid environment.

2. Submersible - a motor, usually totally enclosed in a sealed pump
   housing within an oil bath drives an impeller.  The entire unit
   is designed to be fully or partially submerged in the sump hole.

   The casing may leak at the bearing (if not magnetically coupled) or at the
   wire connections.  Repair of these motors is probably not worth the effort.

Utility pumps are often of the submersible variety.

Three types of automatic switches are commonly used:

1. Float/weight on a wire, rod, or string pulls on a spring action toggle
   type switch.  The length of the linkage is adjusted for the appropriate
   low and high water settings.  These will be used mostly with pedestal
   pumps.  If properly sized, this type of switch can be quite reliable - I
   have a sump pump using this type of switch which is easily 30 years old
   at this point without ever having any problems with the switch.

2. Mercury tilt switch sealed inside a rubber float.  By fastening its
   connecting wire to a suitable location, the level of the water will
   cause the float to pivot from horizontal the more vertical.  An enclosed
   mercury switch then controls power to the pump motor.  These are not
   serviceable but replacements are readily available.

3. Diaphragm pressure switch designed to sense the depth of the water from
   the trapped pressure.  As above, these are not really serviceable but
   can be easily replaced by the same or a mercury type (2).

Most common problems are with switches that are no longer reliable or totally
broken.  Universal replacements are generally available since the switch is
not usually an integral part of the motor/pump unit.

  7.108) Toys

Since there are a semiinfinite number of variations on electrically powered
toys, the only comment I have is that these are almost always combinations
of small PM motors, switches, batteries, light bulbs - and totally impossible
to identify electronic components.  With small kids, physical destruction is
probably a much more common occurrence than a part failure!

  7.109) Garage door operators

Typical garage door operators use a 1/3 to 3/4 horsepower induction motor
with a belt drive chain or screw mechanism to move the 'trolley' that actually
grabs the door.  A switch or pair of switches activated at each end of travel
stops the motor and toggles the state (up or down) of the controller.  Door
blockage sensors detect obstructions and stop or reverse travel.  A light
turns on with motor start and stays on for 3-5 minutes thereafter, controlled
by a simple timer.

Parts of a typical garage door operator (chain drive).  Details may differ
on operators with worm screw or other drive schemes.

1. Motor - single phase induction motor of about 1/2 horsepower at 862 or 1725
   (or so) RPM.  It is electrically reversible with a large ratio V-belt drive
   (probably about 25:1 for a 1725 RPM motor between motor shaft and chain

2. Chain or screw drive - often needs lubrication.  Make sure grease will
   not harden at low temperatures if relevant (e.g., Lubriplate).

3. Limit switches - set top and bottom positions of door.

4. Safety stop - a means of sensing when excessive force is required to move
   the door.  Some types use a compliant motor mount such that excessive
   torque will result in a twist which closes a set of contacts to reverse
   or stop the door.

5. Logic controller - a some relays or a microcontroller.

6. Remote receiver - a radio receiver tuned to the frequency of the hand
   unit.  Logic here or in the controller checks the transmission to 
   determine if the codes match.  More sophisticated units employ a
   pseudo-random code changing scheme to reduce the chance of code theft.
   This is usually in a box on the wall connected to the motor unit by a
   pair of wires.

7. Light bulbs and timer - in many Sears as others, the timer is a bimetal
   strip heated to operate a set of contacts.  The on-time is determined by
   how long it takes for the bimetal strip to cool.  These fail after about
   10 years but replacements are readily available.

  7.110) General garage door operator problems

1. No response from remote or local buttons.  Test power to both the motor
   unit and control box (they may be separate) outlets.  The operator or
   some other device might have blown a fuse or tripped a circuit breaker.
   Verify that the connection between the wall box and the motor unit is in
   tact - check the screw terminals on the motor unit - a wire may have fallen
   off.  Check the circuit breaker (red button) on the motor unit - an overload
   or an undetected cycling condition (an obstruction causing the door to keep
   going up and down continuously) may have tripped it.  Warning: pressing
   this button may result in the door starting to move immediately.

2. Local (inside) buttons work but remote unit is dead.  Check and/or replace
   batteries in the remote unit, confirm that the the code settings have not
   accidentally changed (unit dropped, for example), go through the set up
   procedure outlined in your users manual.  Find a cooperative neighbor with
   the same model and try their remote unit (after writing down their settings
   and reprogramming it for your door).  If this works, your remote unit is
   bad.  If this does not work, you have a receiver problem.

3. Motor operates (you can hear it) but door does not move.  This can be caused
   by a broken or loose belt, snapped door counterbalance spring, locked door,
   disconnected or broken trolley, logic problems causing the motor be turning
   in the wrong direction, and other mechanical problems.  If the motor
   runs for about the normal time, then the trolley is probably moving but
   not attached to the door.  If it runs until forever or the overload pops,
   then a broken belt is likely.

4. Door opens or closes part way and reverses, stops, or twitches back and

   * The tracks may need lubrication, there may be an obstruction like a broom
     that fell over into the vertical rails.

   * The gear timing may be messed up.  The upper and lower limits may be
     determined by switches operated from a cam separate from the trolley that
     moves the door.  If you just reassembled the mechanism, this is a likely

   * The safety stop sensors may be set to be too sensitive.

   * In extremely cold weather, the grease may simply be too viscous or just
     gummed up.

5. Door opens and closes at random.  There can be several possible causes:

   * A neighbor has a similar model and has selected the same code (probably
     the factory default - did you actually ever pick your own code?).

   * Interference from nearby high power amateur, CB, or military or commercial
     radio transmitters may be  confusing the receiver.  Suggest to them that
     they relocate :-).

     Are there such things as IR remote controls for garage door openers
     instead of the usual radio frequency variety?

   * The push button switch on your one of your remotes or receiver module
     is defective - a weak or broken spring - and it is activating the door
     due to vibration or just because it feels like it.  Test the switches.
     On the hand units, you can just remove the batteries for a day and see
     if the door stops misbehaving.

  7.111) Garage door operator light does not work correctly

Assuming the unit otherwise operates normally and you have tried replacing
the light bulb(s):

For many types (Sears, Genie, etc.), there is a thermally operated
time delay consisting of a coil of resistance wire, a bimetal strip,
and a set of contacts.  When the operator is activated, power is applied
to the heater which causes the bimetal strip to bend and close the
contacts turning on the light.  Due to the mass of the bimetal strip,
it takes a couple of minutes to cool down and this keeps the light on.

The most common failure is for the fine wire in the heater to break at
some point.  If you can locate the break, it may be repairable at least
as a temporary solution.  You cannot solder it, however, so a tiny
nut and bolt or crimp will be needed.  However, sticking contacts resulting
in a light that does not always go off are also possible.  Cleaning the
contacts may help.

This part is very easily accessed once the sheetmetal cover is removed.
It is probably somewhere in the middle of the unit fastened with three
screws.  Just remember to unplug the operator first!

Depending on the manufacturer, the original part may be available.  I
know that it is for Sears models.

You could also use a time delay relay or a solid state circuit (RC delay
controlling a triac, for example) but an exact replacement should be just
a whole lot less hassle.

  7.112) Garage door operator loses track of where it is

You press the button to close the door and it works fine.  However, next
time you press the button to make the door go up and it tries to go down into
the ground.

When it gets to the end of the track - be it at the top or bottom, there
must be something that it trips to shut down the motor.  At the same time,
this is supposed to set things up so that the next activation will reverse
the door.

Does the door stop and shut off when it reaches the end or does it eventually
just give up and trip on the safety?

When it trips the switch to stop at the end of its travel, some mechanism
is toggled to change the 'state' of the door logic so that it knows to
go up the next time it is activated.  It is probably this device - be it a
latching relay, mechanical two position switch, or a logic flip flop - that
is not being properly toggled.

I would recommend attempting to determine what device that switch is actually
supposed to toggle - it probably is in the operator unit itself (not the
control box).

  7.113) Garage door remotes behave differently

"I've got 2 Genie garage door remotes.  One of them works from about 100 yards
 away; the other I almost have to be right next to receiver.  I suspect that
 the antenna is the problem; either too short, or blocked by something."

First compare the antennas on the two remotes.  If they are the same and
there are no broken connections, your problem lies elsewhere.  The chance
of the wire itself being bad is pretty slim.

It could also be that the receiver and transmitter frequencies are not quite
identical.  If the remote units have been abused, this is more likely.  I
don't know about Genie but my (old) Sears has trimmers and I was able to
adjust it *very* slightly to match that of the receiver and boost sensitivity.

CAUTION: If you try this (1) mark the exact position where it was originally
and (2) do it only on the transmitter that has the problem.  This will minimize
the possibility of shifting the frequency to where it might interfere with
other devices.  See the section: "Adjusting garage door operator remote unit"
for more information.

  7.114) Adjusting garage door operator remote unit

This situation may arise if one hand unit operates normally but the other
has a very short range.  If you have only one hand unit, it might also be
the problem though not likely to have just happened on its own - either
it was improperly set up at the factory (if new) or hand unit was dropped
once too often.

It should not work at all if the switches are set improperly.  In such a
case, first test and/or replace the battery.  If this does not help, check
the switch settings.

The tuning is done via a variable capacitor trimmer (probably).

There will probably be a trimmer inside the hand unit (don't touch the one
in the receiver).  Position yourself at a reasonable distance and use a
plastic tool to adjust it until the door operates while holding the button
down.  The door will respond at increasing distances as you approach the
optimal setting.

Note: mark the original position first in case this has no effect!

This assumes there is an adjustment - if there is none, you may have an
actual electronic failure, bad connections, etc.

  7.115) Improving sensitivity of garage door openers receivers

Where a garage is constructed with aluminum siding, the remote signal may
be significantly attenuated and of insufficient strength to activate the
receiver module (inside the garage) of the opener at any useful distance
or at all.  Assuming the system operates normally otherwise (i.e., activation
is normal with the door open), two approaches (either or both together) can
be taken to solve this problem:

1. Locate the receiver module (well, actually, its antenna) in an area of
   unsided wood, glass window, or other non-metallic area of the building.
   Note that construction insulation may use aluminum foil as part of its
   vapor barrier so there could be problems even in an area with no siding.

2. Extend the antenna on the receiver module.  This may not always work but
   is worth a try.  A 1 or 2 foot length of copper wire may help dramatically.

3. There are external antenna kits available for some door openers.  The
   antenna goes outside, and connects to the receiver through a hole in
   the wall using coaxial cable.  You will probably have to go directly
   to the manufacturer of your garage door opener or a garage door opener
   service company.

  7.116) Universal remote/receiver units for garage door operators

So you lost your garage door remote or it got run over by your 4x4 :-).  Or,
it just expired due to age.  There are alternatives other than an entire new
operator if the remote is no longer available:

(From: Kirk Kerekes (redgate@tulsa.oklahoma.net)).

Go to a home center, and wander over to the garage door openers. Nearby,
you will find GDO accessories, and among the accessories will be a universal
replacement remote kit that includes a receiver, a transmitter and possibly
a power supply. For about $40, you can by and install the receiver in place of
the existing receiver. If your home center carries Genie openers, you can even
get an Intellicode add-on unit that uses Genie's scanner-proof code-hopping

  7.117) Garage door operator doesn't work reliably in cold weather

First, check the lubrication.  The most common problem is likely to be
gummed up grease in the chain drive (if used) or the bearings of the
rollers.  Note: the track itself generally doesn't require lubrication.
Increasing the safety override force settings may help but are not a wise
solution as the door will then be more of a hazard to any legitimate
obstructions like people and pets.

Another possibility is that the motor start/run capacitor has weakened
and is not permitting the motor to provide the proper torque.  You can
test the capacitor if you have a DMM with a capacitance scale or LCR meter.
Better yet, just replace it.

  7.118) Chamberland garage door opener repair?

"My remote broke for my very old (defunct) chamberlain automatic garage
 door opener.

 Chamberlain tech support told me they suggest I buy a whole new unit. Is
 there any other way to make my door usable with a different remote, or
 some other arrangement?"

(From: Panayiotis Panayi (panikos@mishka.win-uk.net)).

Which Chamberlain operator is it, i.e. which model number. You can
buy the handsets for Chamberlain operators up to 5 years old. If it
is older you will have to buy a new Rx & Tx for it. Most operators
have three screw terminals  on the back for the attachment of Rxs.
The old Chamberlain operators conformed to this. The new ones have
the Rx built onto the main PCB inside the operator and have 4
screws externally for pushbuttons and infra red safety beams. If
yours has 4 screws you will have to provide a separate PSU for the
new Rx or solder two pieces of wire after the step down
transformer on the PCB. You must do it before the rectifiers.
Otherwise the current drain from the Rx will be too big for them.
Besides almost all modern separate Rxs take 24 VAC.

  7.119) Garage door operator security

While manufacturers of garage door operators make excellent claims of
security, this is of no value if you don't take advantage of whatever
features are included in your unit. 

If there is access to your house from the garage, this security is even more
critical.  Once inside the garage, a burglar can work in privacy at their
leisure - and a nice set of tools is probably there for their convenience
in getting through your inside door!  Filling up a good sized car or truck
with loot - again in complete privacy - drive out and close the door behind.
No one will be the wiser until you get back.

1. DIP switches.  Many garage door operators use a set of 8, 12, 16, or
   more little switches to set the codes of the remote and base unit.
   If you have never set these, then your are probably still using the
   manufacturer's default - and all instances of the same model probably
   have the same code!  Change it to something random - pick a number
   out of a random page in a telephone directory or something like that.
   Do not select something cute - others, perhaps with not totally honest
   intentions - will think the same way.  You don't have to remember it so
   an arbitrary totally random setting is fine.  However, even the types with
   24 switches - that is over 16 million possible codes - can be sniffed:
   a relatively simple device can monitor your transmission as you open the
   door and program a special remote unit to duplicate it.

2. More sophisticated units incorporate a scheme whereby the codes change
   each time the operator is used in a pseudo-random manner which is almost
   impossible to duplicate.  Even sniffing such a code is of no use as the
   next instance is not predictable.

3. Don't leave your remote unit prominently displayed in your car - it is
   an inviting target.  Theft is not necessary - just a moment to copy down
   the switch settings may be enough.  Lock your car!  Also, leave a bogus
   remote unit in plain view (from your previous operator).

4. Just because the codes are secure doesn't mean that you are safe.  The
   keylocks that are present on many operators to open the door from the
   outside are pretty pathetic.  They can be picked in about the same time
   it takes to use a key - with ordinary tools - or often with any key that
   will fit the keyhole.  My advice: replace with a high quality pick
   resistant keyswitch.  A well designed electronic lock may be best.  When
   going away for an extended period, use the physical lock on the garage
   door itself as added protection and unplug the garage door operator.

  7.120) Identifying unknown transformer ratings in garage door operator

In a garage door operator, the transformer likely powers the controller
and receiver.  If you can look at where its outputs go, you may be able to
infer something about the voltage even if the transformer is a charred mass.

* If there are AC relays in the box, they almost certainly run off the
  transformer and their coil voltage will be the same if it is the only

* Check the capacitors in the power supplies of the controller and/or
  receiver.  They will give an indication of the approximate secondary
  voltage of the transformer.  Their voltage rating will typically be
  1.5 to 2 times the RMS of the transformer.

* Many of these transformers include a thermal fuse under the outer wrappings
  of insulating material.  These may fail from old age or due to a fault.
  If the transformer works fine without overheating when replaced (or bypassed
  temporarily on a fused circuit), then it may be fine.  However, shorted
  windings can cause a thermal fuse to blow and there is then no electrical
  test that will reveal the proper output voltage.

* Disassemble the transformer and count the number of turns of the primary
  and secondary windings.  The ratio multiplied by 115 is the output voltage.

* Get a 24 V transformer (it is probably not more than this) and connect its
  primary to a Variac and its secondary to the opener.  Slowly increase the
  variac  until everything works. (check every volt or so from 5 to 24).
  Measure the output voltage of the transformer, add 10-20%, you've probably
  got the secondary rating.  If it is near a standard value like 12 or 24,
  this is most likely correct.

* Buy a new opener.

  7.121) Electromechanical doorbells and chimes

Most of these consist of a low voltage transformer powered directly from
the house wiring providing 10 to 20 VAC at its output, one or more switches
for the front door(s), one or more switches for the back door(s), and an
electromagnetic chimes unit.

All of the switches for a given location (i.e., inside and outside the storm
door) are wired in parallel.  There will be three terminals on the chimes
unit - Common (C), Front (F), and Back or Rear (B or R).  This notation may
differ slightly for your unit.  Typical wiring is shown below.  An optional
second chimes unit is shown (e.g., in the basement or master bedroom - more
can be added in parallel as long as the bell transformer had an adequate VA

             Bell Transformer                         Chimes
          H o----+                                     Unit
                  )||       X      _|_ Front door        F
                  )|| +-----+------- --------------------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B
   (Junction box) )||(      +------- --------------------o
                  )||(      Y                            C
                  )|| +----------------------------------o
          N o----+

* The primary side of the transformer is generally wired permanently inside
  a junction box.  This could be almost anywhere but the most common location
  is near the main electrical service panel.

* The common goes to terminal 1 of the transformer (the designation 1 and 2
  is arbitrary - it may not be marked).

* All the front door buttons are wired in parallel and this combination
  connects between terminal 2 of the transformer and the F terminal of the
  chimes unit.

* All the back door buttons are wired in parallel and this combination
  connects between terminal 2 of the transformer and the B or R terminal of
  the chimes unit.

Where the pushbuttons are lighted, a small incandescent bulb is wired across
the switch contacts and mounted inside the button unit.  It is unlikely that
this bulb will ever burn out since it is run at greatly reduced voltage.
However, if the button does not light but the bell works, this has happened.
Replace the pushbutton/light combination - locating a replacement bulb may
not worth the effort though Radio Shack is supposed to have something that
will work.

Most 'not-chiming' problems are due to the one or more of the following:

* Defective switches - these do go bad due to weather and use.  Test with
  a multimeter on the AC voltage range.  You should see the transformer voltage
  across the switch when it is not pressed and near 0 voltage across it
  when it is pressed.  If only one location does not work, a defective switch
  is likely.  Sometimes the wires just come loose or corrode at the terminals.
  These can be cleaned - with fine sandpaper if necessary - and reconnected.

  Note: where multiple switches operate the chimes from similar locations,
  multiple wires may be connected to each switch terminal.  Don' mix these up
  or lose them inside the wall!

* Bad connections.  These could be anywhere but unless you just did some
  renovation which may have damaged the wiring, the most likely locations
  are at the switches, transformer terminals, or chimes.  However, this
  sort of installation might have been done by just twisting wires together
  when extra length was needed and these can go bad.  They could be anywhere.
  Good luck finding the corroded twists!  Then, use Wire Nuts(tm) or solder
  them together to assure reliability in the future.

  If just a single location doesn't work, that should narrows down the problem.
  If only one switch does not work, first test the switch.  If disconnecting
  the wires from the switch does not result in full transformer voltage across
  the wires, then there is a bad connection between you and the transformer,
  the transformer has no power, is defective, or there is a short circuit

* Incorrect wiring at chimes unit.  This commonly happens when someone replaces
  the chimes unit and forgets to label the wires :-(.  It is often difficult
  to follow the wires since they pass through door jams, finished basement
  ceilings, and may not be color coded.  But checking it is easy to with a
  multimeter or the chimes themselves.  An assistant would be helpful - else
  you can just short across the front or back buttons as required below.

  1. Disconnect the wires from the chimes unit terminal block.

  2. Have your assistant press the front door button.

  3. Determine which pair of wires has full voltage - use the multimeter or
     touch them between C and F on the chimes unit.  Make a note of which ones
     they are.  One of these wires is will be C and the other is F.

     Note: due to coupling between the wires, there may be some voltage across
     all combinations.  The most will be across the relevant one (and this will
     be the only combination that will sound the chimes if you are using them
     as a voltage indicator).
  4. Have you assistant press the back door button.

  5. Determine which pair of wires now has voltage.

  6. Connect the wire that is the same as one of those in (3) to the C
     terminal, the other wire of the pair to B, and the remaining wire to F.

* Bad transformer or loss of power to transformer.  The transformer will
  often be located near the main service panel but not always.  Sometimes it
  is a challenge to locate!  To test, proceed as follows (this can be done
  with power on - the low voltage is safe but test first to make sure you
  have the correct transformer!):

  1. Disconnect one of the wires from its output terminals and then test across
     it with a multimeter on the AC voltage range.  There should be the full
     rated transformer voltage across these terminals (actually, it will
     probably be 10 to 20 percent greater).  The rated voltage of the
     transformer should be marked on it somewhere.

     - If there is voltage and it is approximately equal to the transformer's
       rated voltage, the transformer is probably good.

     - If there is none, check for a blown fuse, tripped breaker, or tripped
       GFCI; some other equipment may have overloaded the circuit.  Actual
       failure of the transformer blowing a fuse or tripping a breaker is

       A quick test to determine if the transformer is being powered is to
       feel it!  The transformer should be warm but not hot to the touch.  If
       it is stone cold, either there is no power or a bad connection in the
       input line) circuit.

     - If there is voltage and it is approximately equal to the transformer's

     - If the voltage is much lower than the rated voltage, the transformer
       may be bad.  In this case, it will likely be quite hot due to a short
       circuit inside.

  2. Assuming the voltage checks out, reconnect the wire your previously

  3. If it is now low or 0, there is a short circuit somewhere.  Note: a short
     on the secondary of this type of transformer will cause it to run quite
     hot but may not result in a blown fuse or tripped breaker or even any
     permanent damage to the transformer.

  4. If the chimes sound as you reconnect the wire, there is a short in or
     at one of the pushbutton switches or associated wiring.

  5. If the voltage remains the same, then the transformer is probably good
     and the problem lies elsewhere - bad switch, bad connection, defective

* Dirty or defective chimes.  Most common problems are not electrical but
  mechanical - the plungers that strike the actual chime or gong do not move
  freely due to dirt and grime (especially in a kitchen location) or corrosion.
  Usually, wiping them clean or some light sanding will restore perfect
  operation.  Do not lubricate as the oil will just collect crud and you will
  be doing this again in the near future.  If they move freely, then you have
  an electrical problem.  Also note that these chimes are designed to be
  mounted with the plungers moving vertically.  There is likely a 'this side
  up' indication on the unit - if you are experiencing problems with a new
  installation in particular, verify your mounting!

  Test for voltage between the Common and Front or Back terminals when the
  appropriate button is pressed.

  - If correct voltage is present, disconnect the non-common wire and check the
    resistance between the Common and the terminal for the chime that is not
    working - it should be reasonably low, under 100 ohms.  If the resistance
    is infinite, the coil is open.  Unless you can locate the broken wire, the
    chimes unit will need to be replaced.

  - If the voltage is missing, the problem is probably elsewhere.

  - If the voltage is low, there may be a partial short in the coil, the
    transformer may be underrated for your chimes (not all chimes take the
    same amount of power), or there may be a high resistance somewhere else
    in the wiring.

  7.122) Adding an additional set of chimes

There are at least two ways of doing this (though the first one is more
straightforward and intuitive and therefore generally preferred).

1. Locate the wires going to the first chimes unit.  There will be either 2
   or 3 (both front and back door).  Connect the new chimes unit to these
   same wires in parallel:

             Bell Transformer                         Chimes    Chimes
          H o----+                                    Unit 1    Unit 2
                  )||       X      _|_ Front door        F         F
                  )|| +-----+------- --------------------o---------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B         B
   (Junction box) )||(      +------- --------------------o---------o
                  )||(      Y                            C         C
                  )|| +----------------------------------o---------o
          N o----+

   The only concern is whether the existing transformer that operates the
   chimes has enough capacity - you may need to replace it with one with a
   higher 'VA' rating (the voltage rating should be the same).  These are
   readily available at hardware and electrical supply stores and home

   Some people might suggest just paralleling an additional transformer across
   the original one (which may be possible if the output phases match).  I
   would really recommend simply replacing it.  (This is probably easier
   mechanically in any case.)  Unless the transformers output voltages as
   designed are identical, there will be some current flowing around the
   secondaries at all the times.  At the very least, this will waste power
   ($$) though overheating is a possibility as well.

2. Each additional chimes unit or group of chimes units can use its own
   transformer but share the doorbell pushbuttons.  Just wire point 'X' of the
   transformers together and each point 'Y' separately to the C (common)
   terminal on its respective chimes unit(s):

             Bell Transformer                         Chimes    Chimes
          H o----+                                    Unit 1    Unit 2
                  )||       X      _|_ Front door        F         F
                  )|| +-----+------- --------------------o---------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B         B
   (Junction box) )||(      +------- --------------------o---------o
                  )||(      Y                            C         C
                  )|| +----------------------------------o    +----o
                  )||                                         |
          N o----+        From output Y of identical o--------+
                           second bell transformer
                           (H, N, X, wired in parallel)

   However, since the 'Y' outputs of the transformers are connected at all
   times to the 'C' terminals of the of the chimes units AND the 'X' outputs
   are tied together, any voltage difference between the 'Y' outputs will
   result in current flow through the chimes coils even if no button is
   pressed.  Thus, the transformers must be phased such that there is no (or
   very little) voltage between 'Y' outputs.  Test between 'Y' outputs with a
   multimeter set on AC Volts after you have the transformers powered: if you
   measure about double the transformer voltage rating (e.g., 32 VAC), swap
   ONE set of transformer leads (input or output but not both) and test again.
   If it is still more than a couple volts, your transformers are not matched
   well enough and you should purchase identical transformers or use the
   approach in (1), above.
Note: For either of these schemes, beyond some number of chimes units, the
current rating of the pushbutton switches will be exceeded resulting in early
failure.  However, this should not happen unless your house is similar in size
to Bill Gates' mansion.

* Another alternative:  If you have an unused baby monitor type intercom (your
  kid is now in college), stick the transmitter next to the main chimes and put
  the receiver in your workshop or wherever you want it :-).

  7.123) How to add an addition button to a door bell

Refer to the diagram in the section: "Electromechanical doorbells and chimes",

Another button can be added in parallel with any of the existing ones (i.e.,
between points X and F or X and B in the diagram).  The only restriction is
that you may not be able to have more than one lighted button in each group
as the current passing through the lighted bulbs may be enough to sound the
chimes - at least weakly.

If you cannot trace the wiring (it is buried inside the wall or ceiling)
the only unknown is which side of the transformer to use.  If you pick the
wrong one, nothing will happen when you press the button.

  7.124) Wireless doorbells or chimes

The transmitter and receiver portion of these units are virtually identical
to those of garage door operators.  See the relevant sections on those units
for problems with activation.

The bell or chimes portion may be either an electromechanical type - a coil
forming an electromagnet which pulls in a plunger to strike a gong or bell.
See the section: "Electromechanical doorbells and chimes".

Others are fully electronic synthesizing an appropriate tone, series of tones,
or even a complete tune on demand.  Repair of the electronics is beyond the
scope of this document.  However, there are several simple things that can
be done:

* Check for dead batteries and dirty battery contacts in both the pushbutton
  and chimes unit.

* Confirm that the channel selection settings have not accidentally been
  changed on the pushbutton or chimes unit.  Flick each switch back and
  forth (where switches are used) just to make sure they are firmly seated.

* Check for improper programming or program loss due to a power failure (if
  AC operated) on units that are more sophisticated than a personal computer.

  7.125) Doorbell rings on its own

* For mechanical chimes, this is almost certainly an intermittent short
  circuit in the button wiring or a defective button.  First check or replace
  the outside pushbutton switches as this is the most likely location due to
  environment and small multilegged creatures.

* For electronics chimes, the problem could either be in the transmitter(s) or
  chimes unit or due to external interference.  Someone in your vicinity could
  have the model also set to the default code (which is probably what you
  have, correct?).

  First, remove the batteries or kill power to all transmitters and wait see if
  the problem still occurs.

  - If it does, either the chimes unit is defective or there is an external
    source of interference.

  - If it now behaves, try each one individually to identify the culprit.
    In some cases, a low battery could produce these symptoms as well.

  7.126) Old garage door operator guts for wireless chime

Don't toss the electronic remains of that old garage door operator.  It would
probably be possible to use it as the basis for a wireless doorbell.  Instead
of starting the motor, use its output to enable an electronic chime or buzzer.
The RF transmitter and receiver for a wireless chime is virtually identical
to that of a typical garage door operator.

  7.127) TV antenna rotators

These consist of a base unit with some sort of direction display and knob
and a motor unit to which the TV antenna is mounted.  Of course, the
troubleshooting of these installations is complicated, of course, by the
remote and somewhat inaccessible location of the motor unit :-(.  Before
climbing up on the third story roof, confirm that you haven't lost power
to the motor unit and/or base station and that the connections between
them are secure.

A common type of motor that may be used in these is a small AC split phase or
capacitor run induction motor.  The relative phase of the main and phase coils
determines the direction.  These probably run on 115 VAC.  A capacitor may
also be required in series with one of the windings.  If the antenna does not
turn, a bad capacitor or open winding on the motor is possible.  See the
chapter: "Motors 101" for more info on repair of these types of motors.

The base unit is linked to the motor unit in such a way that the motor
windings are powered with the appropriate phase relationship to turn the
antenna based on the position of the direction control knob.  This may
be mechanical - just a set of switch contacts - or electronic - IR detectors,
simple optical encoder, etc.

Chapter 8) Power Tools

  8.1) Types of motors found in power tools

A variety of motor types are used depending on the type of tool.  AC powered
portable tools usually use a universal motor due to it high power/weight
ratio and ease of electronic speed control.  Cordless tools usually use a
high performance permanent magnet DC motor.  Stationary power tools almost
always use some form of AC induction motor except where variable speed
is required.  

See the sections on these types of motors for more details than the following
summaries provide.

  8.2) Motors in AC line operated portable tools

Line operated portable (corded) power tools usually use a universal type
AC motor providing 3,000 to 30,000 RPM at the motor shaft.  For the same
power rating, these will be significantly lighter than an induction motor.

A single or multiple stage gear reducer drops the relatively high speed
at which these motors are most efficient to whatever the tool actually
requires, increasing the torque as well.

Universal motors can also be speed controlled relatively easily using a
variant of a simple light dimmer type circuit.  Excellent torque is
maintained over a very wide range extending to nearly 0 RPM.

  8.3) Motors in cordless power tools

These are usually high performance permanent magnet DC motors using advanced
high strength and exotic magnetic materials.  They are very compact and light
weight for their power output.  As with all DC (brush type) motors, brush
wear is a common problem.

Speed control is easily accomplished by low cost electronic circuits which
chop the power (pulse width modulation) rather than simply using a rheostat.
This is much more efficient - extremely important with any battery operated

  8.4) Motors in stationary power tools

Stationary power tools which do not require continuous speed control will
generally use some type of AC induction motor - split phase or capacitor
start/run.  The motors generally operate at a fixed speed of around either
1725 or 3450 RPM (U.S., 60 Hz power).  Stepped pulleys or continuous mechanical
speed/torque changers are used to obtain (usually) lower work piece speeds.

For example, a typical drill press may have one or two sets of stepped
pulleys providing 3 to 15 or more speeds by changing belt positions.  A
continuously variable cone drive is also available as an option on some
models.  This is extremely convenient but does add cost and is usually not
found on less expensive models.

An internal thermal overload protector may be incorporated into larger
motors.  WARNING: this may be self resetting.  If the tool stops on its own,
switch off and unplug it before attempting to determine the cause.

Generally, these induction motors are virtually maintenance-free though
cleaning, tensioning, and lubrication may be required of the drive system.

However, electronic speed control of induction motors, while possible,
is relatively complex and expensive requiring a variable frequency
variable voltage power supply.  Therefore, universal motors may be used
on stationary tools like scroll saws with continuously variable electronic
speed control.

  8.5) About horsepower ratings

One horsepower is equal to 746 watts of electrical power (100% efficiency).
Therefore, the most you can get continuously from a normal 115 V 15 A outlet
is about 2 HP.  Any claims (for air compressors, for example) of higher
ratings on a normal outlet are totally bogus.  Companies such as Sears
(Craftsman) like to specify 'Reserve Power' for their power tools which
as best as I can determine refers to the power available for a short time
and may relate to the mass - and inertia - of the rotating parts but not
the continuous power available.  This may be useful to help saw through
a tough knot in a piece of hardwood but may not be terribly meaningful for
a wet/dry vacuum!  Therefore, pay most attention to the continuous power
ratings if they can be found anywhere.  A good indication is probably the
maximum amps required for the electrical service.

As with over-the-counter drugs, extra strength does not necessarily translate
into faster relief, higher current does not always mean better performance,
and horsepower ratings much above what you would compute from V x A may be
more of a marketing gimmick than anything really beneficial.

  8.6) Cords for AC line operated portable power tools

Really old power tools had two wire cord plugs and no safety ground yet were
of all metal (solid and heavy!) construction.  I would recommend that as
a matter of policy, these be retrofitted with a 3 wire grounded cordset.

Newer ones have the grounded cordset while the newest 'double insulated
tools' are of mostly plastic construction and are back to a 2 wire ungrounded

As with any electrical appliances, inspect cords regularly and repair or
replace any that are seriously damaged - if the inner wiring is showing,
nicked, or cut; if the plug is broken or gets hot during use, or where
the cord is pulled from or broken at the strain relief.

  8.7) Portable drills

The portable electric drill (now the rage is cordless) is probably one of
the two first tools that any handyman should own (the other being a saber
saw).  It is used for many things in addition to drilling little holes -
drilling large holes, sanding, polishing, driving screws, etc.  Therefore,
these tools get a lot of use - and abuse.

  8.8) AC line powered drills

An AC line powered electric drill is just a universal motor with a two stage
(typical) gear reduced powering a chuck to hold the drill bit or attachment.
A continuous range speed control with a reversing switch is now standard
on most AC line powered drills.

Typical problems include:

* Worn bearings.  These may be replaceable.  Also see the section: "Upgrading
  the bearings on a Craftsman drill".

* Worn motor brushes.  Replacements should be available. from the manufacturer
  or a motor/appliance repair shop.

* Broken or chipped gears.  This is rare under normal conditions but
  if the drill was abused, then failure is possible.

* Bad cord or plug.  Repair or replace for safety reasons.

* Bad speed controller/reversing switch.  Replacement trigger assemblies
  are available but may cost half as much as an entire new drill.  One
  common wear item is the linear potentiometer operated by the trigger
  and this is not likely to be a standard component.  The drill may work
  fine as a single speed model if this control fails.  You could always
  use an inexpensive external motor speed controller in this case.

* Bad motor.  Failures are possible but unless abused, not nearly as common
  as other simple problems like bad brushes or bearings.  It may not be cost
  effective to replace a bad armature or stator unless this is an expensive
  high quality drill or you have a similar model available for parts.

* Rusted or gummed up chuck. (Or, lost chuck key!).  The chuck is replaceable.
  Depending on type, it may mount with a right or left hand screw thread and
  possibly a right or left hand retaining screw through the center.  See the
  owner's manual to determine what your drill uses as you could be attempting
  to tighten rather than loosen the chuck if you turn the wrong way.  If by
  some slight chance you do not have the owner's manual :-), a reversible drill
  will usually have a left hand (reversed) thread on the chuck and a
  retaining screw with a right hand (normal) thread.  A non-reversible drill
  will only have a right hand thread on the chuck and probably no retaining
  screw.  There may be a hole to insert a locking rod to prevent the shaft
  from turning as you attempt to loosen the chuck.  Inserting the chuck key
  or a suitable substitute and gently tapping it with a hammer in the proper
  direction may be useful as well to free the chuck.

  A gummed up but not too badly rusted chuck can be rescued with penetrating
  oil like WD40 or Liquid Wrench: spray it into the chuck, let it sit for few
  minutes, then use the chuck key to start working it back and forth.  Pretty
  soon it should be free - rotate through its entire range back and forth.
  Spray and spin a couple more times and it should be fine for another 20.000

  8.9) Upgrading the bearings on a Craftsman drill

Very inexpensive models (like the $30 Father's day specials) may use sleeve
bearings in various locations instead of better quality longer lived ball or
roller bearings.  One particular bearing tends to deteriorate rapidly,
especially if the drill is used for sanding or in dusty work environments
(as opposed to clean rooms :-) ).  This is the motor bearing at the handle
end.  The lubrication dries out or is absorbed by dust particles, the bearing
runs dry, wears, and fails with an ear shattering squeal.  Even if you use ear
plugs, the speed and power are not adequate as the motor is laboring and
overloaded and motor failure would result from prolonged operation.

I have upgraded a couple of these drills to ball bearings.  The substitution
is straightforward requiring disassembly of the drill - removing of the
front gear reducer and then one side of the case.  At this point, the old
sleeve bearing is easily freed from its mounting (just the plastic of the
case) and pulled from the shaft.  The shaft is likely undamaged unless you
attempted to continue running the drill even after going deaf.

The drills I upgraded had bearings that were 7/8" OD, 5/16" thick, and with
a 5/16" ID center hole.  The old ones were worn by almost 1/32" oversize
for the center hole but the motor shaft was undamaged.  I found suitable
replacement double sealed ball bearings in my junk box but I would assume
that they are fairly standard - possibly even available from Sears Parts as
I bet they are used in the next model up.

If the gear reducer needs to come apart to access the motor, take note of
any spacer washers or other small parts so you can get them back in exactly
the correct locations.  Work in a clean area to avoid contaminating the
grease packing.

The bearing should be a press fit onto the shaft.  Very light sanding of
the shaft with 600 grit sandpaper may be needed - just enough so that the
new bearing can be pressed on.  Or, gently tap the center race with hammer
(protected with a block of wood).  Make sure that the bearing is snug when
mounted so that the outer race cannot rotate - use layers of thin heat
resistant plastic if needed to assure a tight fit (the old sleeve bearing
was keyed but your new ball bearing probably won't have this feature).

These drills now run as smoothly as Sears' much more expensive models.

  8.10) Cordless drills

Cordless drills use a permanent magnet DC motor operating off of a NiCd
(usually) battery pack.  Manufacturers make a big deal out of the voltage
of the pack - 6, 7.2, 9.6, 12, 14, 18, etc. - but this really isn't a sure
measure of power and time between charges as a motor can be designed for any
reasonable voltage.  A gear reducer follows the motor driving a chuck for
holding the drill or screwdriver bit, or attachment.  These are most often
have a single or two speeds with reverse.

In addition to the problems listed in the section: "AC line powered drills",
these are also subject to all the maladies of battery operated appliances.
Cordless tools are particularly vulnerable to battery failure since they
are often use rapid charge (high current) techniques.

* Bad NiCd batteries - reduced capacity or shorted cells.  In most cases,
  a new pack will be required.

* Bad power/speed selection/reversing switch.  Replace.

* Bad motor.  These are usually permanent magnet brushed type motors.
  Worn brushes and bearings are common problems.  In addition, a partially
  shorted motor due to commutator contamination is also possible - see the
  sections on PM DC motors.  Disassembly, cleaning, and lubrication may be

  8.11) Other direct drive tools

* Rotary (Moto) tools - high speed compact universal or PM motors with a
  variety of chucks and adapters for holding tiny bits, grinding stones,
  cutters, etc.

* Routers, biscuit cutters - high speed (30,000 RPM typical) universal
  motor with a 1/4" (fixed size, router) chuck for common router bits.

  Ball bearings are used which have long life but are probably replaceable
  if they fail (noisy, excessive runout, etc.).

  The plug, cord, trigger, and interlock switches are prone to problems and
  should be checked if the tool doesn't run at all.

* String trimmers - universal motor on long handle with trigger control.
  Check for a bad cord, switch, and dirt in the motor if the unit appears
  dead.  The motor brushes could also be worn or not seating properly.

  8.12) Saber saws, reciprocating saws

These use a universal motor which drives a gear reducer and reciprocating
mechanism.  Better models have a variable speed control so that the sawing
rate can be optimized to the work.  All but the most inexpensive allow the
head to be rotated or rotate automatically based on feed direction adding
a bit of complexity.

A reciprocating saw is very similar but uses a much larger motor and beefier

In addition to motor problems, there can be problems with damage, dirt, or
need for lubrication of the reciprocating mechanism.

  8.13) Electric chain saws

WARNING: Read and follow all safety instructions using any type of chain saw.

These have a high power universal motor and gear reducer.  Most have the
motor mounted transversely with normal pinion type gears driving the
chain sprocket.  A few models have the motor mounted along the axis of
the saw - I consider this less desirable as the gyroscopic character of
the rotating motor armature may tend to twist the saw as it is tilted
into the work.

Inexpensive designs suffer from worn (plain) bearings, particularly at the
end of the motor opposite the chain since this is exposed to the elements.
Normal maintenance should probably include cleaning and oiling of this
bearing.  A loud chattering or squealing with loss of speed and power is an
indication of a worn and/or dry bearing  Replacement with a suitable ball
bearing is also a possibility (see the section: "Upgrading the bearings on
a Craftsman drill" since the approach is identical.

Keep the chain sharp.  This is both for cutting efficiency and safety.  A
dull chain will force you to exert more pressure than necessary increasing
the chance of accidents.  Chains can be sharpened by hand using a special
round file and guide or an electric drill attachment.  Alternatively, shops
dealing in chain saws will usually have an inexpensive chain sharpening
service which is well worth the cost if you are not equipped or not inclined
to do it yourself.

One key to long blade and bar life is the liberal use of the recommended
chain oil.  Inexpensive models may have a manual oiler requiring constant
attention but automatic oilers are common.  These are probably better - if
they work.  Make sure the oil passages are clear.

The chain tension should be checked regularly - the chain should be free to
move but not so loose that it can be pulled out of its track on the bar.  This
will need to snugged up from time-to-time by loosening the bar fastening nuts,
turning the adjustment screw, then retightening the nuts securely.

There may be a slip clutch on the drive sprocket to protect the motor if the
chain gets stuck in a log.  After a while, this may loosen resulting in
excessive slippage or the chain stopping even under normal conditions.  The
slip clutch can generally be tightened with a screwdriver or wrench.

  8.14) Circular saws, miter, and cutoff saws

These have a high power universal motor either directly driving the blade
or driving a gear reducer (high torque/large blade variety).

Miter and cutoff saws are similar but are mounted on a tilting mechanism
with accurate alignment guides (laser lights in the most expensive!).

  8.15) Grinding wheels

A dual shaft induction motor drives rotating grinding stones (or other tools
like wire brushes).  Most common are fixed speed - usually around 3450 RPM
but variable speed operation is highly desirable to avoid overheating of
tempered metal during sharpening.  All but the most inexpensive use sealed
ball bearings requiring no routine maintenance.

Small light duty grinders may be 1/4 HP or less.  However, this is adequate
for many home uses.

Wet wheels may run at much slower speeds to keep heat to a minimum.  Being
in close proximity to water may in itself create problems.

  8.16) Polishers, rotary sanders

A gear reduced universal motor drives a rubber (usually) mounting plate
to which a sanding disk or polishing pad is attached.

Due to the nature of their use, sanders in particular may accumulate a lot
of dust and require frequent cleaning and lubrication.

  8.17) Orbital sanders and polishers

In addition to the usual universal motor and its bearings, the orbital
mechanism may require cleaning and greasing periodically.

  8.18) Belt sanders, power planers

A typical portable belt sander uses a gear or belt reduced universal motor
driving one of the rollers that the sanding belt rotates on under tension.
In decent quality tools, these should use ball or roller bearings which require
little attention.

A power planer is similar in many ways but the motor drives a set of cutters
rather than a sanding belt.

  8.19) Air compressors

A direct or belt drive induction motor (probably capacitor start)
powers a single or multiple cylinder piston type compressor.  Typical
continuous motor ratings are between 1/4 and 2 HP (for a 115 VAC line).
Over and under pressure switches are used to maintain the pressure in
an attached storage tank within useful - and safe - limits.  Most will
include an unloading valve to remove pressure on the pistons when the
compressor stops so that it can be easily restarted without damage to
the motor and without blowing fuses or tripping circuit breakers.

I much prefer a belt driven compressor to a direct drive unit.  One
reason is that a motor failure does not render the entire compressor
useless as any standard motor can be substituted.  The direct drive
motor may be a custom unit and locating a replacement cheaply may be

Drain the water that collects in the tank after each use.

Inspect the tank regularly for serious rust or corrosion which could result
in an explosion hazard.as well.

  8.20) Paint sprayers

Traditional air powered paint sprayers may simply be an attachment to an
air compressor or may be a self contained unit with the compressor built in.
Since the active material is paint which dries into a hard mass (what a
concept!), cleaning immediately after use is essential.  Otherwise, strong
solvents will be needed to resurrect a congealed mess - check your user's
manual for acceptable deadly chemicals.

Portable airless paint sprayers use a solenoid-piston mechanism inside the
spray head itself.  There is little to go wrong electrically other than the
trigger switch as long as it is cleaned after use.

Professional airless paint sprayers use a hydraulic pump to force the
paint through a narrow orifice at extremely high pressure like 1000 psi.

With all types, follow the manufacturer's recommendations as to type and
thickness of paint as well as the care and maintenance before and after use
and for storage.

Warning: high performance paint sprayers in particular may be a safety
hazard should you put your finger close to the output orifice accidentally.
The pressures involved could be sufficient to inject paint - and anything
else in the stream - through the skin resulting in serious infection or worse.

  8.21) Heat guns

These are similar to high performance hair dryers and subject to the same
problems - bad cord or switch, open heating element, defective thermostats,
universal motor problems, and just plain dirt and dust buildup.

  8.22) Paint strippers

These are just a high power heating element attached to a cord.  If there
is no heat, check for a bad plug, cord, or open element with your multimeter.

  8.23) Soldering irons

Simple pencil irons use an enclosed heating element is attached to the
'business' end in some manner - screw thread, set screw, clamping ring,
etc.  Failure to heat may be due to a bad plug, cord, bad connections,
or defective element.

Some types package the heating element and replaceable tip in a separate
screw-in assembly.  These are easily interchangeable to select the
appropriate wattage for the job.  Damage is possible to their ceramic
insulator should one be dropped or just from constant use.

High quality temperature controlled soldering stations incorporate some
type of thermostatic control - possibly even with a digital readout.

  8.24) Soldering guns

The common Weller Dual Heat soldering gun is a simple transformer with the
tapped primary winding in the bulk of the case and a single turn secondary
capable of 100 or more amps at around 1.5 V.  The soldering element is simply
a piece of copper (possible with a shaped tip) which is heated due to the high
current passing through it even though it is made mostly of copper.  The
'headlight(s)' (flashlight bulbs) operate off of a winding on the transformer
as well.

Possible problems include:

* No response to trigger - bad cord, bad switch, open transformer primary.

* Low or high (dual heat models) does not work - bad switch, bad transformer

* Lack of sufficient heat - bad connections where soldering element mounts.
  clean and/or tighten.  Tin the tip if needed (not permanently tinned).
  Use the high setting (dual heat models).

* Tip too hot - use the lower setting (if dual heat).  Do not keep the trigger
  depressed for more than 30 seconds or so at a time.  Manually pulse width
  modulate the power level.

* Entire unit overheats - this could be a shorted winding in the transformer
  but more likely is that you are simply not giving it a chance to cool.  It
  is not designed for continuous operation - something like 2 minutes on, 5
  minutes off, is usually recommended.

* No light - bad bulbs, bad connections, bad winding (unlikely).

Note: a soldering gun is not a precision instrument and should not be used
for fine electronics work - you will ruin ICs and printed circuit boards.
(However, I have heard of someone replacing an MC68000 microprocessor (64 pin
DIP) successfully with a large Weller soldering gun!)

  8.25) Wet-dry vacs, yard blowers/vacs

A powerful universal motor driving a centrifugal blower is all there is
in this equipment.  Unfortunately, many common models use cheaply made
motors which may fail simply due to use or from the dust and proximity
to liquids.  The blower sucks air and whatever else into the holding tank.
A filter is supposed to prevent anything from getting through.  The motor
itself should be sealed against direct contact with the dust/liquid section
of the machine.

Problems occur with bad cords, switch, motor brushes, bearings, or a
burnt out motor from excessive use under adverse conditions.

As with inexpensive electric drills, sleeve bearings (usually, the top
bearing which is exposed somewhat) in the motor can become worn or dry.
Replacing with a ball bearing is a worthwhile - but rather involved -
undertaking if this happens.  See the section: "Upgrading
the bearings on a Craftsman drill" as the technique is similar (once you
gain access - not usually a 10 minute job).

  8.26) Hedge trimmers

A gear reduced universal motor drives a reciprocating mechanism not too
dissimilar to a saber saw.  In addition to the usual motor/electrical
problems, lubrication may be needed periodically.  Should you accidentally
try to trim a steel fence instead of a bush, damage to one or more teeth
may occur.  In this case, light filing may be needed to remove nicks and

Of course, you probably will not get away without cutting the power cord
a couple of times as well!  See the sections on power cords.  One way to
avoid the humiliation (other than being half awake) is to wrap a cord
protector around the first 2 or 3 feet of cord at the tool.  This will
make the cord larger in diameter than the inter-tooth spacing preventing
accidental 'chewups'.

  8.27) Electric lawn mowers

A large universal or permanent magnet DC motor drives one or two sets of
rotating blades.  A load or dead short may be thrown across the motor to
act as a dynamic brake when stopping.  As usual, when the mower does not
operate, check for bad plug, cord, switch, brushes, dirt, etc.  See the
sections on motors.

Chapter 9) AC Adapters and Transformers

  9.1) AC adapter basics

It seems that the world now revolves around AC Adapters or 'Wall Warts'
as they tend to be called.  There are several basic types.  Despite the
fact that the plugs to the equipment may be identical THESE CAN GENERALLY
NOT BE INTERCHANGED.  The type (AC or DC), voltage, current capacity, and
polarity are all critical to proper operation of the equipment. Use of an 
improper adapter or even just reverse polarity can permanently damage or
destroy the device.  Most equipment is protected against stupidity to a
greater or lessor degree but don't count on it.

The most common problems are due to failure of the output cable due to
flexing at either the adapter or output plug end.  See section below on
repair procedure.

1. AC Transformer.  All wall warts are often called transformers.  However,
   only if the output is stated to be 'AC' is the device simply a transformer.
   These typically put out anywhere from 3 to 20 VAC or more at 50 mA to
   3 A or more.  The most common range from 6-15 VAC at less than an Amp.
   Typically, the regulation is very poor so that an adapter rated at 12 VAC
   will typically put out 14 VAC with no load and drop to less than 12 VAC
   at rated load.  To gain agency approval, these need to be protected 
   internally so that there is no fire hazard even if the output is shorted.
   There may be a fuse or thermal fuse internally located (and inaccessible).

   If the output tested inside the adapter (assuming that you can get it
   open without total destruction - it is secured with screws and is
   not glued or you are skilled with a hacksaw - measures 0 or very low with no
   load but plugged into a live outlet, either the transformer has failed or
   the internal fuse had blown.  In either case, it is probably easier to
   just buy a new adapter but sometimes these can be repaired.  Occasionally,
   it will be as simple as a bad connection inside the adapter.  Check the
   fine wires connected to the AC plug as well as the output connections.
   There may be a thermal fuse buried under the outer layers of the
   transformer which may have blown.  These can be replaced but locating
   one may prove quite a challenge.

2. DC Power Pack. In addition to a step down transformer, these include at
   the very least a rectifier and filter capacitor.  There may be additional
   regulation but most often there is none.  Thus, while the output is DC,
   the powered equipment will almost always include an electronic regulation.

   As above, you may find bad connections or a blown fuse or thermal fuse
   inside the adapter but the most common problems are with the cable.

3. Switching Power Supply.  These are complete low power AC-DC converters
   using a high frequency inverter.  Most common applications are laptop
   computers and camcorders.  The output(s) will be fairly well regulated
   and these will often accept universal power - 90-250 V AC or DC.

   Again, cable problems predominate but failures of the switching power
   supply components are also possible.  If the output is dead and you have
   eliminated the cable as a possible problem or the output is cycling on
   and off at approximately a 1 second rate, then some part of the switching
   power supply may be bad.  In the first case, it could be a blown fuse,
   bad startup resistor, shorted/open semiconductors, bad controller,
   or other components.  If the output is cycling, it could be a shorted
   diode or capacitor, or a bad controller.  See the "Notes on the
   Troubleshooting and Repair of Small Switchmode Power Supplies" for more
   info, especially on safety while servicing these units.

  9.2) AC adapter testing

AC adapters that are not the switching type (1 and 2 above) can easily
be tested with a VOM or DMM.  The voltage you measure (AC or DC) will
probably be 10-25% higher than the label specification.  If you get no
reading, wiggle, squeeze, squish, and otherwise abuse the cord both at
the wall wart end and at the device end.  You may be able to get it to
make momentary contact and confirm that the adapter itself is functioning.

The most common problem is one or both conductors breaking internally
at one of the ends due to continuous bending and stretching.

Make sure the outlet is live - try a lamp.

Make sure any voltage selector switch is set to the correct position.
Move it back and forth a couple of times to make sure the contacts are clean.

If the voltage readings check out for now, then wiggle the cord as above in
any case to make sure the internal wiring is intact - it may be intermittent.

Although it is possible for the adapter to fail in peculiar ways, a
satisfactory voltage test should indicate that the adapter is functioning

  9.3) Pocket wall adapter tester/polarity checker

This handy low cost device can be built into an old ball point pen case or
something similar to provide a convenient indication of wall adapter type,
operation, and polarity:

            Probe(+) o-----/\/\-----+----|>|----+---o Probe(-)
                         1K, 1/2 W  | Green LED |
                                       Red LED

* The green LED will light up if the polarity of an adapter with a DC output
  agrees with the probe markings.

* The red LED will light up if the polarity of an adapter with a DC output is
  opposite of the probe markings.

* Both LEDs will light up if your adapter puts out AC rather than DC.

* The LED brightness can provide a rough indication of the output voltage.

The operating range is about 3 to 20 V AC or DC.

  9.4) AC adapter repair

Although the cost of a new adapter is usually modest, repair is often
so easy that it makes sense in any case.

The most common problem (and the only one we will deal with here) is the
case of a broken wire internal to the cable at either the wall wart or
device end due to excessive flexing of the cable.

Usually, the point of the break is just at the end of the rubber cable
guard.  If you flex the cable, you will probably see that it bends more easily
here than elsewhere due to the broken inner conductor.  If you are reasonably
dextrous, you can cut the cable at this point, strip the wires back far
enough to get to the good copper, and solder the ends together.  Insulate
completely with several layers of electrical tape.  Make sure you do not
interchange the two wires for DC output adapters!  (They are usually marked
somehow either with a stripe on the insulator, a thread inside with one
of the conductors, or copper and silver colored conductors.  Before you
cut, make a note of the proper hookup just to be sure.  Verify polarity
after the repair with a voltmeter.

The same procedure can be followed if the break is at the device plug end
but you may be able to buy a replacement plug which has solder or screw
terminals rather than attempting to salvage the old one.

Once the repair is complete, test for correct voltage and polarity before
connecting the powered equipment.

This repair may not be pretty, but it will work fine, is safe, and will
last a long time if done carefully.

If the adapter can be opened - it is assembled with screws rather than
being glued together - then you can run the good part of the cable inside
and solder directly to the internal terminals.  Again, verify the polarity
before you plug in your expensive equipment.

Warning:  If this is a switching power supply type of adapter, there are
dangerous voltages present inside in addition to the actual line connections.
Do not touch any parts of the internal circuitry when plugged in and make
sure the large filter capacitor is discharged (test with a voltmeter)
before touching or doing any work on the circuit board.  For more info on
switching power supply repair, refer to the document: "Notes on the
Troubleshooting and Repair of Small Switchmode Power Supplies".

If it is a normal adapter, then the only danger when open are direct
connections to the AC plug.  Stay clear when it is plugged in.

  9.5) AC adapter substitution and equipment damage

Those voltage and current ratings are there for a reason.  You may get
away with a lower voltage or current adapter without permanent damage but
using a higher voltage adapter is playing Russian Roulette.  Even using
an adapter from a different device - even with similar ratings, may
be risky because there is no real standard.  A 12 V adapter from one
manufacturer may put out 12 V at all times whereas one from another
manufacturer may put out 20 V or more when unloaded.

A variety of types of protection are often incorporated into adapter
powered equipment.  Sometimes these actually will save the day.
Unfortunately, designers cannot anticipate all the creative techniques
people use to prove they really do not have a clue of what they are doing.

The worst seems to be where an attempt is made to operate portable devices
off of an automotive electrical system.  Fireworks are often the result,
see below and the section on: "Automotive power".

If you tried an incorrect adapter and the device now does not work there
are several possibilities (assuming the adapter survived and this is not
the problem):

1. An internal fuse blew.  This would be the easiest to repair.

2. A protection diode sacrificed itself.  This is usually reverse biased
   across the input and is supposed to short out the adapter if the
   polarity is reversed.  However, it may have failed shorted particularly
   if you used a high current adapter (or automotive power).

3. Some really expensive hard to obtain parts blew up.  Unfortunately,
   this outcome is all too common.

Some devices are designed in such a way that they will survive almost anything.
A series diode would protect against reverse polarity.  Alternatively, a large
parallel diode with upstream current limiting resistor or PTC thermistor, and
fuses, fusable resistors, or IC protectors would cut off current before the
parallel diode or circuit board traces have time to vaporize.  A crowbar
circuit (zener to trigger an SCR) could be used to protect against reasonable

I inherited a Sony Discman from a guy who thought he would save a few bucks and
make an adapter cord to use it in his car.  Not only was the 12-15 volts
from the car battery too high but he got it backwards!  Blew the DC-DC
converter transistor in two despite the built in reverse voltage protection
and fried the microcontroller.  Needless to say, the player was a loss but the
cigarette lighter fuse was happy as a clam!

Moral: those voltage, current, and polarity ratings marked on portable
equipment are there for a reason.  Voltage rating should not be exceeded,
though using a slightly lower voltage adapter will probably cause no harm
though performance may suffer.  The current rating of the adapter should
be at least equal to the printed rating.  The polarity, of course, must be
correct.  If connected backwards with a current limited adapter, there may be
no immediate damage depending on the design of the protective circuits.  But
don't take chances - double check that the polarities match - with a voltmeter
if necessary - before you plug it in!  Note that even some identically marked
adapters put out widely different open circuit voltages.  If the unloaded
voltage reading is more than 25-30% higher than the marked value, I would
be cautious about using the adapter without confirmation that it is acceptable
for your equipment.  Needless to say, if you experience any strange or
unexpected behavior with a new adapter, if any part gets unusually warm, or if
there is any unusual odor, unplug it immediately and attempt to identify the
cause of the problem.

  9.6) Replacing batteries with an AC adapter

While most appliances that run off of internal batteries also include a socket
for an wall adapter, this is not always the case.  Just because there is no
hole to plug one in doesn't necessarily mean that you cannot use one.

The type we are considering in this discussion are plug-in wall adapter that
output a DC voltage (not AC transformers).  This would be stated on the

The first major consideration is voltage.  This needs to be matched to the
needs of the equipment.  However, what you provide may also need to be well
regulated for several reasons as the manufacturer may have saved on the cost
of the circuitry by assuming the use of batteries:

* The maximum voltage supplied by a battery is well defined.  For example,
  4 AA cells provide just over 6 V when new.  The design of the device may
  assume that this voltage is never exceeded and include no internal regulator.
  Overheating or failure may result immediately or down the road with a wall
  adapter which supplies more voltage than its nameplate rating (as most do
  especially when lightly loaded).

* Most wall adapters do not include much filtering.  With audio equipment,
  this may mean that there will be unacceptable levels of hum if used direct.
  There are exceptions.  However, there is no way of telling without actually
  testing the adapter under load.

* The load on the power source (batteries or adapter) may vary quite a bit
  depending on what the device is doing.  Fresh batteries can provide quite
  a bit of current without their voltage drooping that much.  This is not
  always the case with wall adapters and the performance of the equipment
  may suffer.

Thus, the typical universal adapter found at Radio Shack and others may not
work satisfactorily.  No-load voltage can be much higher than the voltage at
full load - which in itself may be greater than the marked voltage.  Adding
an external regulator to a somewhat higher voltage wall adapter is best.  See
the section: "Adding an IC regulator to a wall adapter or battery".

The other major consideration is current.  The rating of the was adapter must
be at least equal to the *maximum* current - mA or A - drawn by the device
in any mode which lasts more than a fraction of a second.  The best way to
determine this is to measure it using fresh batteries and checking all modes.
Add a safety factor of 10 to 25 percent to your maximum reading and use this
when selecting an adapter.

For shock and fire safety, any wall adapter you use should be isolated and
have UL approval.

* Isolation means that there is a transformer in the adapter to protect you
  and your equipment from direct connection to the power line.  Most of the
  inexpensive type do have a transformer.  However, if what you have weighs
  almost nothing and is in a tiny case, it may be meant for a specific purpose
  and not be isolated.

* UL (Underwriters Lab) approval means that the adapter has been tested to
  destruction and it is unlikely that a fire would result from any reasonable
  external fault like a prolonged short circuit.

To wire it in, it is best to obtain a socket like those used on appliances
with external adapter inputs - from something that is lying in your junk-box
or a distributor like MCM Electronics.  Use one with an automatic disconnect
(3 terminals) if possible.  Then, you can retain the optional use of the
battery.  Cut the wire to the battery for the side that will be the outer
ring of the adapter plug and wire it in series with the disconnect (make
sure the disconnected terminal goes to the battery and the other terminal
goes to the equipment).  The common (center) terminal goes to other side of
the battery, adapter, and equipment as shown in the example below.  In this
wiring diagram, it is assumed that the ring is + and the center is -.  Your
adapter could be wired either way.  Don't get it backwards!

                       X V  | (Inserting plug breaks connection at X)
      Battery (+) o-------  |
      Adapter (+) o---------+------------------o Equipment (Ring, +)
      Battery/                            |
      Adapter (-) o-----------------------+----o Equipment (Center, -)

Warning: if you do not use an automatic disconnect socket, remove the battery
holder or otherwise disable it - accidentally using the wall adapter with
the batteries installed could result in leakage or even an explosion!

  9.7) Converting an AC output wall adapter to DC

Where a modest source of DC is required for an appliance or other device,
it may be possible to add a rectifier and filter capacitor (and possibly
a regulator as well) to a wall adapter with an AC output.  While many wall
adapter output DC, some - modems and some phone answering machines, for
example - are just transformers and output low voltage AC.

This is also the simplest and safest way to construct a small DC power supply
as you do not need to deal with the 110 VAC at all.

To convert such an adapter to DC requires the use of:

    * Bridge rectifier - turns AC into pulsating DC.
    * Filter capacitor - smoothes the output reducing its ripple.
    * Regulator - produces a nearly constant output voltage.

Depending on your needs, you may find a suitable wall adapter in your junk
box (maybe from that 2400 baud modem that was all the rage a couple of years

The basic circuit is shown below:

            Bridge Rectifier   Filter Capacitor

    AC o-----+----|>|-------+---------+-----o DC (+)
            ~|              |+        |
   In from   +----|<|----+  |       +_|_   Out to powered device
   AC wall               |  |      C ---   or voltage regulator
   Adapter   +----|>|----|--+       - |
             |           |            |
    AC o-----+----|<|----+------------+-----o DC (-)
            ~                -


* An AC input of Vin VRMS will result in a peak output of approximately
  1.4 Vin - 1.4 V.  The first factor of 1.4 results from the fact that the
  peak value of a sinusoid (the power line waveform) is 1.414 (sqrt(2))
  times the RMS value.  The second factor of 1.4 is due to the two diodes
  that are in series as part of the bridge rectifier.  The fact that they
  are both about 1.4 is a total coincidence.

  Therefore, you will need to find an AC wall adapter that produces an output
  voltage which will result in something close to what you need.  However,
  this may be a bit more difficult than it sounds since the nameplate rating
  of many wall adapters is not an accurate indication of what they actually
  produce especially when lightly loaded.  Measuring the output is best.

* Select the filter capacitor to be at least 10,000 uF per 1000 mA of output
  current with a voltage rating of at least 2 x Vin.  This rule of thumb will
  result in a ripple of less than 1 V p-p which will be acceptable for many
  devices or where a voltage regulator is used (but may be inadequate for
  some audio devices resulting in some 120 Hz hum.  Use a larger or additional
  capacitor or a regulator in such a case.

* Suitable components can be purchased at any electronics distributor as well
  as Radio Shack.  The bridge rectifier comes as a single unit or you can put
  one together from 1N400x diodes (the x can be anything from 1 to 7 for these
  low voltage applications).  Observe the polarity for the filter capacitor!

The following examples illustrate some of the possibilities.

* Example 1: A typical modem power pack is rated at 12 VAC but actually
  produces around 14 VAC at modest load (say half the nameplate current
  rating).  This will result in about 17 to 18 VDC at the output of the
  rectifier and filter capacitor.

* Example 2: A cordless VAC battery charger adapter might produce 6 VAC.
  This would result in 6 to 7 VDC at the output of the rectifier and filter

Adding an IC regulator to either of these would permit an output of up to
about 2.5 V less than the filtered DC voltage.

  9.8) Adding an IC regulator to a wall adapter or battery

For many applications, it is desirable to have a well regulated source of
DC power.  This may be the case when running equipment from batteries as
well as from a wall adapter that outputs a DC voltage or the enhanced adapter
described in the section: "Converting an AC output wall adapter to DC".

The following is a very basic introduction to the construction of a circuit
with appropriate modifications will work for outputs in the range of about
1.25 to 35 V and currents up 1 A.  This can also be used as the basis for a
small general purpose power supply for use with electronics experiments.

What you want is an IC called an 'adjustable voltage regulator'.  LM317 is one
example - Radio Shack should have it along with a schematic.  The LM317 looks
like a power transistor but is a complete regulator on a chip.

Where the output needs to be a common value like +5 V or -12 V, ICs called
'fixed voltage regulators' are available which are preprogrammed for these.
Typical ICs have designations of 78xx (positive output) and 79xx (negative

For example:

            Positive                   Negative
        Voltage Regulator          Voltage Regulator
     -----------------------    -----------------------
         7805      +5 V             7905      -5 V
         7809      +9 V             7909      -9 V
         7812     +12 V             7912     -12 V
         7815     +15 V             7915     -15 V

and so forth.  Where these will suffice, the circuit below can be simplified
by eliminating the resistors and tying the third terminal to ground.  Note:
pinouts differ between positive and negatve types - check the datasheet!

Here is a sample circuit using LM317:

                    I +-------+ O                       
    Vin (+) o-----+---| LM317 |---+--------------+-----o Vout (+)
                  |   +-------+   |              |
                  |       | A     /              |
                  |       |       \ R1 = 240     |
                  |       |       /              |           ___
                 _|_ C1   |       |            +_|_ C2      |_0_|  LM317
                 --- .01  +-------+             --- 1 uF    |   |  1 - Adjust
                  |  uF   |                    - |          |___|  2 - Output
                  |       \                      |           |||   3 - Input
                  |       / R2                   |           123
                  |       \                      |
                  |       |                      |
    Vin(-) o------+-------+----------------------+-----o Vout (-)

Note: Not all voltage regulator ICs use this pinout.  If you are not using an
LM317, double check its pinout - as well as all the other specifications.

For the LM317:

1. R2 = (192 x Vout) - 240, where R2 in ohms, Vout is in volts and must be at
   between 1.2 V and 35 V.

2. Vin should be at least 2.5V greater than Vout.  Select a wall adapter with
   a voltage at least 2.5 V greater than your regulated output at full load.

   However, note that a typical adapter's voltage may vary quite a bit
   depending on manufacturer and load.  You will have to select one that
   isn't too much greater than what you really want since this will add
   unnecessary wasted power in the device and additional heat dissipation.

3. Maximum output current is 1 A.  Your adapter must be capable of supplying
   the maximum current safely and without its voltage drooping below the
   requirement in (2) above.

4. Additional filter capacitance (across C1) on the adapter's output may help
   (or be required) to reduce its ripple and thus the swing of its input.
   This may allow you to use an adapter with a lower output voltage and reduce
   the power dissipation in the regulator as well.

   Using 10,000 uF per *amp* of output current will result in less than 1 V
   p-p ripple on the input to the regulator.  As long as the input is always
   greater than your desired output voltage plus 2.5 V, the regulator will
   totally remove this ripple resulting in a constant DC output independent
   of line voltage and load current fluctuations.  (For you purists, the
   regulator isn't quite perfect but is good enough for most applications.)

   Make sure you select a capacitor with a voltage rating at least 25% greater
   than the adapter's *unloaded* peak output voltage and observe the polarity!

   Note: wall adapters designed as battery chargers may not have any filter
   capacitors so this will definitely be needed with this type.  Quick check:
   If the voltage on the adapter's output drops to zero as soon as it is pulled
   from the wall - even with no load - it does not have a filter capacitor.

5. The tab of the LM317 is connected to the center pin - keep this in mind
   because the chip will have to be on a heat sink if it will be dissipating
   more than a watt or so.  P = (Vout - Vin) * Iout.  

6. There are other considerations - check the datasheet for the LM317
   particularly if you are running near the limits of 35 V and/or 1 A.

  9.9) Testing a power transformer

Here are some simple tests to perform where you want to determine if a used
(or new) power transformer with known specifications is actually good:

0. Look for obvious signs of distress.  Smell it to determine if there is any
   indication of previous overheating, burning, etc.

1. Plug it in and check for output voltages to be reasonably close (probably
   somewhat high) to what you expect.

2. Leave it on for awhile.  It may get anywhere from just detectable to
   moderately warm but not to hot to touch and it shouldn't melt down, smoke,
   or blow up.  Needless to say, if it does any of the latter, the tests are

3. Find a suitable load based on: R = V/I from the specifications and make
   sure it can supply the current without overheating.  The voltage should
   also not drop excessively between no and full load (but this depends on the
   design, quality of constructions, whether you got it at Radio Shack :-),

  9.10) Determining power (VA) ratings of unknown transformers

For a transformer with a single output winding, measuring temperature rise
isn't a bad way to go.  Since you don't know what an acceptable temperature
is for the transformer, a conservative approach is to load it - increase
the current gradually - until it runs warm to the touch after an extended
period (say an hour) of time.

Where multiple output windings are involved, this is more difficult since
the safe currents from each are unknown.

(From: Greg Szekeres (szekeres@pitt.edu)).
Generally, the VA rating of individual secondary taps can be measured.  While
measuring the no load voltage, start to load the winding until the voltage
drops 10%, stop measure the voltage and measure or compute the current. 10%
would be a very safe value. A cheap transformer may compute the VA rating with
a 20% drop. 15% is considered good. You will have to play around with it to
make sure everything is ok with no overheating, etc.

(From: James Meyer (jimbob@acpub.duke.edu)).

With the open circuit voltage of the individual windings, and their DC
resistance, you can make a very reasonable assumption as to the relative
amounts of power available at each winding.

Set up something like a spread-sheet model and adjust the output current to
make the losses equal in each secondary.  The major factor in any winding's
safe power capability is wire size since the volts per turn and therefore the
winding's length is fixed for any particular output voltage.  

  9.11) Determining the ratings of a fried power transformer

A power transformer can die in a number of ways.  The following are the most

* Primary open.  This usually is the result of a power surge but could also
  be a short on the output leading to overheating.

  Since the primary is open, the transformer is totally lifeless.

  First, confirm that the transformer is indeed beyond redemption.  Some have
  thermal or normal fuses under the outer layer of insulating tape or paper.

* Short in primary or secondary.  This may have been the result of overheating
  or just due to poor manufacturing but for whatever reason, two wires are
  touching.  One or more outputs may be dead and even those that provide some
  voltage may be low.

  The transformer may now blow the equipment fuse and even if it does not,
  probably overheats very quickly.

  First, make sure that it isn't a problem in the equipment being powered.
  Disconnect all outputs of the transformer and confirm that it still has
  nearly the same symptoms.

There are several approaches to analyzing the blown transformer and/or
identifying what is needed as a replacement:

* If you have the time and patience and the transformer is not totally sealed
  in Epoxy or varnish, disassembling it and counting the number of turns of
  wire for each of the windings may be the surest approach.  This isn't as bad
  as it sounds.  The total time required from start to dumping the remains in
  the trash will likely be less than 20 minutes for a small power transformer.

  Remove the case and frame (if any) and separate and discard the (iron) core.
  The insulating tape or paper can then be pealed off revealing each of the 
  windings.  The secondaries will be the outer ones.  The primary will be the
  last - closest to the center.  As you unwind the wires, count the number of
  full turns around the form or bobbin.

  By counting turns, you will know the precise (open circuit) voltages of each
  of the outputs.  Even if the primary is a melted charred mass, enough of the
  wire will likely be intact to permit a fairly accurate count.  Don't worry,
  an error of a few turns between friends won't matter.

  Measuring the wire size will help to determine the relative amount of
  current each of the outputs was able to supply.  The overall ratings of
  the transformer are probably more reliably found from the wattage listed
  on the equipment nameplate.

If you cannot do this for whatever reason, some educated guesswork will be
required.  Each of the outputs will likely drive either a half wave (one
diode), full wave (2 diodes if it has a centertap), or bridge (module or
4 diodes).  For the bridge, there might be a centertap as well to provide
both a positive and negative output.

* You can sometimes estimate the voltage needed by looking at the components
  in the power supply - filter cap voltage ratings and regulators.

* The capacitor voltage ratings will give you an upper bound - they are
  probably going to be at least 25 to 50 percent above the PEAK of the input

* Where there are regulators, their type and ratings and/or the circuit itself
  may reveal what the expected output will be and thus the required input
  voltage to the regulators.  For example, if there is a 7805 regulator chip,
  you will know that its input must be greater than about 7.5 V (valleys of
  the ripple) to produce a solid 5 V output.

* If there are no regulators, then the ICs, relays, motors, whatever, that
  are powered may have voltage and current ratings indicating what power
  supply is expected (min-max).

  9.12) Determining wiring of unknown power transformer

"I recently purchased at a local electronics surplus store at 35volt center
 tap 2A transformer for a model railroad throttle (power supply).  The
 secondary wires are red-red/yellow-red and I understand how to hook up the
 secondary in order to get two 17.5 volt sources.  My dilemma is the
 primary.  There are SIX black wires (black, black/red, black/blue,
 black/green, black/yellow, black/grey).  Two of the wires were already
 stripped and I hooked these up to 115 VAC but no voltage on the secondary
 side.  Does anyone have any ideas?  I don't know the manufacturer, the
 transformer is in an enclosed case (no open windings).  I also don't know
 if it has multiple primaries that must be connected or if it has five taps
 for different input voltages.  Any ideas????"

Of course, I assume you did measure on the AC scale on the secondary! :-)
Sorry, have to confirm the basics.  My natural assumption would also be
that the striped wires were the ones you needed.

Here is a suggestion:

1. Use an ohmmeter to determine which sets of primary wires are connected.
   The resistances will be very low but you should also be able to determine
   which are just taps as the resistance between them will be very low.

2. Since you already know what the secondary should be, power the secondary
   from a low voltage AC source like another transformer.  Then measure
   across each pair of primary wires.  You should be able to determine
   which are the main wires and which are the taps.

Using a combination of the above procedures should enable you to pretty
fully determine what is going on.  I suspect that you have a pair of
primary windings that can be connected either series (for 220) or parallel
(110) and a tap but who knows.  Do the tests.  If in doubt, don't just
connect it to 110 - you could end up with a melt-down.  Post your findings.

  9.13) Transformer repair

Some power transformers include a thermal fuse under the outer layers of
insulation.  In many cases, an overload will result in a thermal fuse opening
and if you can get at it, replacement will restore the transformer to health.

Where an open thermal fuse is not the problem, aside from bad solder or crimp
connections where the wire leads or terminals connect to the transformer
windings, anything else will require unwrapping one or more of the windings to
locate an open or short.  Where a total melt-down has occurred and the result
is a charred hunk of copper and iron, even more drastic measures would be

In principle, it would be possible to totally rebuild a faulty transformer.
All that is needed is to determine the number of turns, direction, layer
distribution and order for each winding.  Suitable magnet (sometimes called
motor wire) is readily available.

However, unless you really know what you are doing and obtain the proper
insulating material and varnish, long term reliability and safety are unknown.
Therefore, I would definitely recommend obtaining a proper commercial
replacement if at all possible.

However, DIY transformer construction is nothing new:

(From: Robert Blum (rfblum@worldnet.att.net)).

I have a book from the Government Printing Office . The title is: "Information
for the Amateur Designer of Transformers for 25 to 60 cycle circuits" by
Herbert B. Brooks. It was issued June 14, 1935 so I do not know if it is still
in print.  At the time I got it it cost $.10.

(From: Mark Zenier (mzenier@netcom.com)).

"Practical Transformer Design Handbook" by Eric Lowdon.  Trouble is, last I
checked it's out of print.  Published by both Sams and Tab Professional Books.

(From: Paul Giancaterino (PAULYGS@prodigy.net)).

I found a decent article on the subject in Radio Electronics,
May 1983. The article explains the basics, including how to figure what
amps your transformer can handle and how to size the wiring.

Chapter 10) Batteries

  10.1) Battery technology

The desire for portable power seems to be increasing exponentially with
the proliferation of notebook and palmtop computers, electronic organizers,
PDAs, cellular phones and faxes, pagers, pocket cameras, camcorders and
audio cassette recorders, boomboxes - the list is endless.

Two of the hottest areas in engineering these days are in developing
higher capacity battery technologies (electrochemical systems) for
rechargeable equipment and in the implementation of smart power management
(optimal charging and high efficiency power conversion) for portable devices.
Lithium and Nickel Metal Hydride are among the more recent additions to
the inventory of popular battery technologies.  A variety of ICs are now
available to implement rapid charging techniques while preserving battery
life.  Low cost DC-DC converter designs are capable of generating whatever
voltages are required by the equipment at over 90% efficiency

However, most of the devices you are likely to encounter still use pretty
basic battery technologies - most commonly throwaway Alkaline and Lithium
followed by rechargeable Nickel Cadmium or Lead-Acid.  The charging circuits
are often very simple and don't really do the best job but it is adequate
for many applications.

For more detailed information on all aspects of battery technology, see
the articles at:


There is more on batteries than you ever dreamed of ever needing.  The
sections below represent just a brief introduction.

  10.2) Battery basics

A battery is, strictly speaking, made up of a number of individual cells
(most often wired in series to provide multiples of the basic cell voltage
for the battery technology - 1.2, 1.5, 2.0, or 3.0 V are most common).
However, the term is popularly used even for single cells.

Four types of batteries are typically used in consumer electronic equipment:

1. Alkaline - consisting of one or more primary cells with a nominal terminal
   voltage of 1.5 V.  Examples are AAA, AA, C, D, N, 9V ('transistor'),
   lantern batteries (6V or more), etc.  There are many other available
   sizes including miniature button cells for specialty applications like
   clocks, watches, calculators, and cameras.  In general recharging of
   alkaline batteries is not practical due to their chemistry and
   construction.  Exceptions which work (if not entirely consistently as of
   this writing) are the rechargeable Alkalines (e.g., 'Renewals').
   Advantages of alkalines are high capacity and long shelf life.  These now
   dominate the primary battery marketplace largely replacing the original
   carbon-zinc and heavy duty types.  Note that under most conditions, it
   not necessary to store alkaline batteries in the 'fridge to obtain maximum
   shelf life.

2. Lithium - these primary cells have a much higher capacity than alkalines.
   The terminal voltage is around 3 volts per cell.  These are often used
   in cameras where their high cost is offset by the convenience of long life
   and compact size.  Lithium batteries in common sizes like 9V are beginning
   to appear.  In general, I would not recommend the use of lithiums for use
   in applications where a device can be accidentally left on - particularly
   with kids' toys.  Your batteries will be drained overnight whether
   a cheap carbon zinc or a costly lithium.  However, for smoke alarms,
   the lithium 9V battery (assuming they hold up to their longevity claims)
   is ideal as a 5-10 year service life without attention can be expected.

3. Nickel Cadmium (NiCd) - these are the most common type of rechargeable 
   battery technology use in small electronic devices.  They are available in
   all the poplar sizes.  However, their terminal voltage is only 1.2 V per
   cell compared to 1.5 V per cell for alkalines (unloaded).  This is not the 
   whole story, however, as NiCds terminal voltage holds up better under load
   and as they are discharged.  Manufacturers claim 500-1000 charge-discharge
   cycles but expect to achieve these optimistic ratings only under certain
   types of applications.  In particular it is usually recommended that
   NiCds should not be discharged below about 1 V per cell and should not
   be left in a discharged state for too long.  Overcharging is also an enemy
   of NiCds and will reduce their ultimate life.  An electric shaver is an
   example of a device that will approach this cycle life as it is used
   until the battery starts to poop out and then immediately put on charge.
   If a device is used and then neglected (like a seldom used printing
   calculator), don't be surprised to find that the NiCd battery will not
   charge or will not hold a charge next time the calculator is used.

4. Lead Acid - similar to the type used in your automobile but generally
   specially designed in a sealed package which cannot leak acid under most
   conditions.  These come in a wide variety of capacities but not in standard
   sizes like AA or D.  They are used in some camcorders, flashlights, CD
   players, security systems, emergency lighting, and many other applications.
   Nominal terminal voltage is 2.0 V per cell.  These batteries definitely do
   not like to be left in a discharged condition (even more so than NiCds) and
   will quickly become unusable if left that way for any length of time.

  10.3) Battery chargers

The (energy storage) capacity, C, of a battery is measured in ampere hours
denoted a A-h (or mA-h for smaller types).  The charging rate is normally
expressed as a fraction of C - e.g., .5 C or C/2.

In most cases, trickle charging at a slow rate - C/100 to C/20 - is easier on
batteries.  Where this is convenient, you will likely see better performance
and longer life.  Such an approach should be less expensive in the long run
even if it means having extra cells or packs on hand to pop in when the others
are being charged.  Fast charging is hard on batteries - it generates heat and
gasses and the chemical reactions may be less uniform.

Each type of battery requires a different type of charging technique.

1. NiCd batteries are charged with a controlled (usually constant) current.
   Fast charge may be performed at as high as a .5-1C rate for the types of
   batteries in portable tools and laptop computers.  (C here is the amp-hour
   capacity of the battery.  A .5C charge rate for a 2 amp hour battery
   pack would use a current equal to 1 A, for example.)  Trickle charge at a
   1/20-1/10C rate.  Sophisticated charges will use a variety of techniques
   to sense end-of-charge.  Inexpensive chargers (and the type in many cheap
   consumer electronics devices) simply trickle charge at a constant current.
   Rapid chargers for portable tools, laptop computers, and camcorders, do at
   least sense the temperature rise which is one indication of having reached
   full charge but this is far from totally reliable and some damage is
   probably unavoidable as some cells reach full charge before others due
   to slight unavoidable differences in capacity.  Better charging techniques
   depend on sensing the slight voltage drop that occurs when full charge
   is reached but even this can be deceptive.  The best power management
   techniques use a combination of sensing and precise control of charge
   to each cell, knowledge about the battery's characteristics, and state
   of charge.

   While slow charging is better for NiCds, long term trickle charging is
   generally not recommended.

   Problems with simple NiCd battery chargers are usually pretty easy to
   find - bad transformer, rectifiers, capacitors, possibly a regulator.
   Where temperature sensing is used, the sensor in the battery pack may
   be defective and there may be problems in the control circuits as well.
   However, more sophisticated power management systems controlled by
   microprocessors or custom ICs and may be impossible to troubleshoot for
   anything beyond obviously bad parts or bad connections.

2. Lead acid batteries are charged with a current limited but voltage
   cutoff technique.  Although the terminal voltage of a lead-acid battery is
   2.00 V per cell nominal, it may actually reach more than 2.5 V per
   cell while charging.  For an automotive battery, 15 V is still within
   the normal range of voltages to be found on the battery terminals when
   the engine (and alternator) are running.

   A simple charger for a lead-acid battery is simply a stepped down rectified
   AC source with some resistance to provide current limiting.  The current
   will naturally taper off as the battery voltage approaches the peaks
   of the charging waveform.  This is how inexpensive automotive battery
   chargers are constructed.  For small sealed lead-acid batteries, an IC
   regulator may be used to provide current limited constant voltage charging.
   A 1 A (max) charger for a 12 V battery may use an LM317, 3 resistors,
   and two capacitors, running off of a 15 V or greater input supply.

   Trickle chargers for lead-acid batteries are usually constant voltage and
   current tapers off as the battery reaches full charge.  Therefore, leaving
   the battery under constant charge is acceptable and will maintain it at the
   desired state of full charge.

   Problems with lead-acid battery chargers are usually pretty easy to
   diagnose due to the simplicity of most designs.

  10.4) Substituting NiCds for Alkalines

First note that rechargeable batteries are NOT suitable for safety critical
applications like smoke detectors unless they are used only as emergency
power fail backup (the smoke detector is also plugged into the AC line) and
are on continuous trickle charge).  NiCds self discharge (with no load) at
a rate which will cause them to go dead in a month or two.

For many toys and games, portable phones, tape players and CD players, and
boomboxes, TVs, palmtop computers, and other battery gobbling gadgets, it
may be possible to substitute rechargeable batteries for disposable primary
batteries.  However, NiCds have a lower terminal voltage - 1.2V vs. 1.5V - and
some devices will just not be happy.  In particular, tape players may not
work well due to this reduced voltage not being able to power the motor
at a constant correct speed.  Manufacturers may specifically warn
against their use.  Flashlights will not be as bright unless the light
bulb is also replaced with a lower voltage type.  Other equipment may
perform poorly or fail to operate entirely on NiCds.  When in doubt, check
your instruction manual.

  10.5) Can a large electrolytic capacitor be substituted for a NiCd?

The quick answer is: probably not.  The charger very likely assumes that
the NiCds will limit voltage.  The circuits found in many common appliances
just use a voltage source significantly higher than the terminal voltage
of the battery pack through a current limiting resistor.  If you replace
the NiCd with a capacitor and the voltage will end up much higher than
expected with unknown consequences.  For more sophisticated chargers, the
results might be even more unpredictable.

Furthermore, even a SuperCap cannot begin to compare to a small NiCd for
capacity.  A 5.5 V 1 F (that's Farad) capacitor holds about 15 W-s of energy
which is roughly equivalent to a 5 V battery of 3 A-s capacity - less than
1 mA-h.  A very tiny NiCd pack is 100 mA-h or two orders of magnitude larger.

  10.6) Determining the actual capacity of a NiCd battery

When a battery pack is not performing up to expectations or is not marked
in terms of capacity, here are some comments on experimentally determining
the A-h rating.

When laying eggs, start with a chicken.  Actually, you have to estimate
the capacity so that charge and discharge rates can be approximated.
However, this is usually easy to do with a factor of 2 either way just be

        Size of cells       Capacity range, A-h
             AAA               .2 - .4
             AA                .4 - 1
             C                  1 - 2
             D                  1 - 5
        Cordless phone         .1 - .3
          Camcorder             1 - 3+
       Laptop computer          1 - 5+

First, you must charge the battery fully.  For a battery that does not
appear to have full capacity, this may be the only problem.  Your charger
may be cutting off prematurely due to a fault in the charger and not the
battery.  This could be due to dirty or corroded contacts on the charger
or battery, bad connections, faulty temperature sensor or other end-of-charge
control circuitry. Monitoring the current during charge to determine if the
battery is getting roughly the correct A-h to charge it fully would be a
desirable first step.  Figure about 1.2 to 1.5 times the A-h of the battery
capacity to bring it to full charge.

Then discharge at approximately a C/20 - C/10 rate until the cell voltages
drops to about 1 V (don't discharge until flat or damage may occur).  Capacity
is calculated as average current x elapsed time since the current for a NiCd
will be fairly constant until very near the end.

  10.7) NiCd batteries and the infamous 'memory effect'

Whether the NiCd 'memory effect' is fact or fiction seems to depend on
one's point of view and anecdotal evidence.  What most people think is
due to the memory effect is more accurately described as voltage
depression - reduced voltage (and therefore, reduced power and capacity)
during use.

(The next section is from: Bob Myers (myers@fc.hp.com) and are based on a
 GE technical note on NiCd batteries.)

The following are the most common causes of application problems wrongly
attributed to 'memory':

1. Cutoff voltage too high - basically, since NiCds have such a flat
   voltage vs. discharge characteristic, using voltage sensing to determine
   when the battery is nearly empty can be tricky; an improper setting coupled
   with a slight voltage depression can cause many products to call a battery
   "dead" even when nearly the full capacity remains usable (albeit at a 
   slightly reduced voltage).

2. High temperature conditions - NiCds suffer under high-temp conditions; such
   environments reduce both the charge that will be accepted by the cells
   when charging, and the voltage across the battery when charged (and the
   latter, of course, ties back into the above problem).

3. Voltage depression due to long-term overcharge - Self-explanatory.  NiCds
   can drop 0.1-0.15 V/cell if exposed to a long-term (i.e., a period of
   months) overcharge.  Such an overcharge is not unheard-of in consumer gear,
   especially if the user gets in the habit of leaving the unit in a charger
   of simplistic design (but which was intended to provide enough current for
   a relatively rapid charge).  As a precaution, I do NOT leave any of my
   NiCd gear on a charger longer than the recommended time UNLESS the charger
   is specifically designed for long-term "trickle charging", and explicitly
   identified as such by the manufacturer.

4. There are a number of other possible causes listed in a "miscellaneous"
   category; these include -

  * Operation below 0 degrees C.
  * High discharge rates (above 5C) if not specifically designed for such use.
  * Inadequate charging time or a defective charger.
  * One or more defective or worn-out cells.  They do not last forever.

To close with a quote from the GE note:

"To recap, we can say that true 'memory' is exceedingly rare.  When we see
poor battery performance attributed to 'memory', it is almost always certain
to be a correctable application problem.  Of the...problems noted above,
Voltage Depression is the one most often mistaken for 'memory'.....

This information should dispel many of the myths that exaggerate the idea of
a 'memory' phenomenon."

  10.8) Care and feeding of NiCds

Here are six guidelines to follow which will hopefully avoid voltage
depression or the memory effect or whatever:

(Portions of the following guidelines are
 from the NiCd FAQ written by: Ken A. Nishimura (KO6AF))

1. DON'T deliberately discharge the batteries to avoid memory.  You risk
   reverse charging one or more cell which is a sure way of killing them.

2. DO let the cells discharge to 1.0V/cell on occasion through normal use.

3. DON'T leave the cells on trickle charge for long times, unless voltage
   depression can be tolerated.

4. DO protect the cells from high temperature both in charging and storage.

5. DON'T overcharge the cells.  Use a good charging technique.  With most
   inexpensive equipment, the charging circuits are not intelligent and will
   not terminate properly - only charge for as long as recommended in the
   user manual.

6. DO choose cells wisely.  Sponge/foam plates will not tolerate high
   charge/discharge currents as well as sintered plate.  Of course, it
   is rare that this choice exists.

Author's note: I refuse to get involved in the flame wars with respect
to NiCd battery myths and legends --- sam.

  10.9) Why there will never actually be closure on this topic

(From: Mark Kinsler (kinsler@froggy.frognet.net)).

All of which tends to support my basic operating theory about the charging of
nickel-cadmium batteries:

1) Man is born in sin and must somehow arrange for the salvation of his
   immortal soul. 

2) All nickel-cadmium batteries must be recharged.

3) There is no proper method of performing either task (1) or task (2) to the
   satisfaction of anyone.  

  10.10) NiCd battery pack will not hold a charge

This applies if the pack appears to charge normally and the terminal
voltage immediately after charging is at least 1.2 x n where n is the
number of cells in the pack but after a couple of days, the terminal
voltage has dropped drastically.  For example, a 12 V pack reads only 6 V
48 hours after charging without being used.

What is most likely happening is that several of the NiCd cells have
high leakage current and drain themselves quite rapidly.  If they are
bad enough, then a substantial fraction of the charging current itself is
being wasted so that even right after charging, their capacity is less
than expected.  However, in many cases, the pack will deliver close to
rated capacity if used immediately after charging.

If the pack is old and unused or abused (especially, it seems, if it
is a fast recharge type of pack), this is quite possible.  The cause
is the growth of fine metallic whiskers called dendrites that partially
shorts the cell(s).  If severe enough, a dead short is created and no
charge at all is possible.

Sometimes this can be repaired temporarily at least by 'zapping' using
a large charged capacitor to blow out the whiskers or dendrites that
are causing the leakage (on a cell-by-cell basis) but my success on
these types of larger or high charge rate packs such as used in laptop
computers or camcorders has been less than spectacular.

  10.11) What is this thing in my NiCd battery pack?

In addition to the NiCd cells, you will often find one or more small parts
that are generally unrecognizable.  Normally, you won't see these until
you have a problem and, ignoring all warnings, open the pack.

If it is a little rectangular silver box in series with one of the positive
or negative terminals of the pack, it is probably a thermostat and is there
to shut down the charging or discharging if the temperature of the pack
rises too high.  If it tests open at room temperature, it is bad.  With
care, you can safely substitute a low value resistor or auto tail light
bulb and see if the original problem goes away or at least the behavior
changes.  However, if there is a dead short somewhere, that device may
have sacrificed its life to protect your equipment or charger and going
beyond this (like shorting it out entirely) should be done with extreme
care.  These may be either mechanical (bimetal strip/contacts) or solid
state (Polyfuse(tm) - increases resistance overcurrent).

If it looks like a small diode or resistor, it could be a temperature
sensing thermistor which is used by the charger to determine that the
cells are heating which in its simple minded way means the cells are being
overcharged and it is should quit charging them.  You can try using a
resistor in place of the thermistor to see if the charger will now
cooperate.  Try a variety of values while monitoring the current or
charge indicators.  However, the problem may actually be in the charger
controller and not the thermistor.  The best approach is to try another pack.

It could be any of a number of other possible components but they all serve
a protective and/or charge related function.

Of course, the part may be bad due to a fault in the charger not shutting
down or not properly limiting the current as well.

  10.12) Zapping NiCds to clear shorted cells

Nickel-Cadmium batteries that have shorted cells can sometimes be rejuvenated -
at least temporarily - by a procedure affectionately called 'zapping'.

The cause of these bad NiCd cells is the formation of conductive filaments
called whiskers or dendrites that pierce the separator and short the positive
and negative electrodes of the cell.  The result is either a cell that will
not take a charge at all or which self discharges in a very short time.  A
high current pulse can sometimes vaporize the filament and clear the short.

The result may be reliable particularly if the battery is under constant
charge (float service) and/or is never discharged fully.  Since there are
still holes in the separator, repeated shorts are quite likely especially if
the battery is discharged fully which seems to promote filament formation,

I have used zapping with long term reliability (with the restrictions
identified above) on NiCds for shavers, Dustbusters, portable phones,
and calculators.

WARNING:  There is some danger in the following procedures as heat is
generated.  The cell may explode!  Take appropriate precautions and don't
overdo it.  If the first few attempts do not work, dump the battery pack.


You will need a DC power supply and a large capacitor - one of those 70,000
uF 40 V types used for filtering in multimegawatt geek type automotive audio
systems, for example.  A smaller capacitor can be tried as well.

Alternatively, a you can use a 50-100 A 5 volt power supply that doesn't mind
(or is protected against) being overloaded or shorted.

Some people recommend the use of a car battery for NiCd zapping.  DO NOT be
tempted - there is nearly unlimited current available and you could end with
a disaster including the possible destruction of that battery, your NiCd,
you, and anything else that is in the vicinity.

OK, you have read the warnings:

Remove the battery pack from the equipment.  Gain access to the shorted
cell(s) by removing the outer covering or case of the battery pack and
test the individual cells with a multimeter.  Since you likely tried
charging the pack, the good cells will be around 1.2 V and the shorted
cells will be exactly 0 V.  You must perform the zapping directly across
each shorted cell for best results.

Connect a pair of heavy duty clip leads - #12 wire would be fine - directly
across the first shorted cell.  Clip your multimeter across the cell
as well to monitor the operation.  Put it on a high enough scale such
that the full voltage of your power supply or capacitor won't cause any
damage to the multimeter.


1. Using the large capacitor:

   Charge the capacitor from a current limited 12-24 V DC power supply.

   Momentarily touch the leads connected across the shorted cell to the
   charged capacitor.  There will be sparks.  The voltage on the cell may
   spike to a high value - up to the charged voltage level on the capacitor.
   The capacitor will discharge almost instantly.

2. Using the high current power supply:

   Turn on the supply.

   Momentarily touch the leads connected across the shorted cell to the
   power supply output.  There will be sparks.  DO NOT maintain contact
   for more than a couple of seconds.  The NiCd may get warm!  While
   the power supply is connected, the voltage on the cell may rise to
   anywhere up to the supply voltage.

Now check the voltage on the (hopefully previously) shorted cell.

If the filaments have blown, the voltage on the cell should have jumped
to anywhere from a few hundred millivolts to the normal 1 V of a
charged NiCd cell.  If there is no change or if the voltage almost
immediately decays back to zero, you can try zapping couple more times
but beyond this is probably not productive.

If the voltage has increased and is relatively stable, immediately
continue charging the repaired cell at the maximum SAFE rate specified
for the battery pack.  Note: if the other cells of the battery pack are
fully charged as is likely if you had attempted to charge the pack, don't
put the entire pack on high current charge as this will damage the other
cells through overcharging.

One easy way is to use your power supply with a current limiting resistor
connected just to the cell you just zapped.  A 1/4 C rate should be
safe and effective but avoid overcharging.  Then trickle charge at
the 1/10 C rate for several hours.  (C here is the amp-hour capacity of
the cell.  Therefore, a 1/10 C rate for a 600 mA NiCd is 50 mA.)

This works better on small cells like AAs than on C or D cells since the
zapping current requirement is lower.  Also, it seems to be more difficult
to reliably restore the quick charge type battery packs in portable tools
and laptop computers that have developed shorted cells (though there are
some success stories).

My experience has been that if you then maintain the battery pack in
float service (on a trickle charger) and/or make sure it never discharges
completely, there is a good chance it will last.  However, allow the
bad cells to discharge to near 0 volts and those mischievous dendrites
will make their may through the separator again and short out the cell(s).

  10.13) Tom's comments on NiCd care and feeding

(From: Tom Lamb (tlamb@gwe.net)).

* Measuring NiCd capacity - I use a very simple/effective system. Put a 2.5
  ohm resistor across the contacts of a cheap travel analog clock, which will
  time the rundown. It is quite consistent for good cells.  A good typical 
  AA NiCd will run one hour.

* NiCd zapping - I use a  1 ohm power resistor in series with a car battery,
  though a series headlight will also work.  I charge for about 30 secs or
  until warm, which will clear the whisker and put in enough charge to see if
  the cell is salvageable.

  10.14) Identifying technology of unmarked battery packs

Since the nominal (rated) voltages for the common battery technologies
differ, it is often possible to identify which type is inside a pack
by the total output voltage:

NiCd packs will be a multiple of 1.2 V.
Lead-acid packs will be a multiple of 2.0 V.
Alkaline packs will be a multiple of 1.5.

Note that these are open circuit voltages and may be very slightly higher
when fully charged or new.

Therefore, it is generally easy to tell what kind of technology is
inside a pack even if the type is not marked as long as the voltage
is.  Of course, there are some - like 6 V that will be ambiguous.

  10.15) Problems with battery operated equipment

For primary batteries like Alkalines, first try a fresh set.  For NiCds,
test across the battery pack after charging overnight (or as recommended
by the manufacturer of the equipment).  The voltage should be 1.2 x n V
where n is the number of cells in the pack.  If it is much lower - off by
a multiple of 1.2 V, one or more cells is shorted and will need to be
replaced or you can attempt zapping it to restore the shorted cells.  See
the section: "Zapping NiCds to clear shorted cells".  Attempt at your own

If the voltage drops when the device is turned on or the batteries are
installed - and the batteries are known to be good - then an overload
may be pulling the voltage down.

Assuming the battery is putting out the proper voltage, then a number of
causes are possible:

1. Corroded contacts or bad connections in the battery holder.

2. Bad connections or broken wires inside the device.

3. Faulty regulator in the internal power supply circuits.  Test
   semiconductors and IC regulators.

4. Faulty DC-DC inverter components.  Test semiconductors and other

5. Defective on/off switch (!!) or logic problem in power control.

6. Other problems in the internal circuitry.

  10.16) Battery juice and corroded contacts

Unless you have just arrived from the other side of the galaxy (where
such problems do not exist), you know that so-called 'leak-proof' batteries
sometimes leak.  This is a lot less common with modern technologies than with
the carbon-zinc cells of the good old days, but still can happen.  It is
always good advice to remove batteries from equipment when it is not being
used for an extended period of time.  Dead batteries also seem to be more
prone to leakage than fresh ones (in some cases because the casing material
is depleted in the chemical reaction which generates electricity and thus
gets thinner or develops actual holes).

In most cases, the actual stuff that leaks from a battery is not 'battery
acid' but rather some other chemical.  For example, alkaline batteries
are so called because their electrolyte is an alkaline material - just the
opposite in reactivity from an acid.  Usually it is not particularly
reactive (but isn't something you would want to eat).

The exception is the lead-acid type where the liquid inside is sulfuric acid
of varying degrees of strength depending on charge.  This is nasty and should
be neutralized with an alkaline material like baking soda before being
cleaned up.  Fortunately, these sealed lead-acid battery packs rarely
leak (though I did find one with a scary looking bulging case, probably
due to overcharging - got rid of that is a hurry).

Scrape dried up battery juice from the battery compartment and contacts
with a plastic or wooden stick and/or wipe any liquid up first with a dry
paper towel.  Then use a damp paper towel to pick up as much residue as
possible.  Dispose of the dirty towels promptly.

If the contacts are corroded, use fine sandpaper or a small file to remove
the corrosion and brighten the metal.  Do not an emery board or emery paper
or steel wool as any of these will leave conductive particles behind which
will be difficult to remove.  If the contacts are eaten through entirely,
you will have to improvise alternate contacts or obtain replacements.
Sometimes the corrosion extends to the solder and circuit board traces as
well and some additional repairs may be needed - possible requiring
disassembly to gain access to the wiring.

  10.17) Automotive power

While it is tempting to want to use your car's battery as a power source
for small portable appliances, audio equipment, and laptop computers,
beware: the power available from your car's electrical system is not
pretty.  The voltage can vary from 9 (0 for a dead battery) to 15 V under
normal conditions and much higher spikes or excursions are possible.
Unless the equipment is designed specifically for such power, you are
taking a serious risk that it will be damaged or blown away.

Furthermore, there is essentially unlimited current available from the
battery (cigarette lighter) - 20 A or more.  This will instantly turn
your expensive CD player to toast should you get the connections wrong.
No amount of internal protection can protect equipment from fools.

My recommendation for laptop computers is to use a commercially available
DC-AC inverter with the laptop's normal AC power pack.  This is not the
most efficient but is the safest and should maintain the laptop's warranty
should something go wrong.  For CD players and other audio equipment, only
use approved automotive adapters.

  10.18) Exploding batteries - these things really happen

(From: Greg Raines (ghr@ix.netcom.com)).

When I was about 10 years old I was sitting in my dad's driveway in a '65
Plymouth Fury III station wagon while he disconnected the trickle charger from
the '67 Fiat in the garage.  I heard a pop and saw my dad throw his hands over
his face, run to the back door and start kicking it to get someone to open it.
Fortunately he wasn't injured.  But it was an eye opener.  It was probably 30
or below, there was no flame present, and the double garage door was open (this
happened in Connecticut).  Also in a Fiat 850 sport coupe the battery is in the
trunk (front) so there really isn't anything up there that would cause a spark
(engine & gas tank in back).  So it must have been a spark off of the charger
when he pulled it off the terminal (he hadn't unplugged the charger).

  10.19) Soldering tabs onto NiCd batteries

When replacing NiCd batteries in packs or portable tools, it is often
necessary to attach wires to the individual cells.  It may be possible to
obtain NiCds with solder tabs attached (Radio Shack has these) but if
yours do not, here are two ways that work.  They both require a (Weller)
high wattage soldering gun.

I use a high power Weller (140 W) soldering gun.  Use fine sandpaper to
thoroughly clean and roughen up the surface of the battery cell at both
ends.  Tin the wires ahead of time as well.  Arrange the wire and cell
so that they are in their final position - use a vise or clamp or buddy
to do this.  Heat up the soldering gun but do not touch it to the battery
until it is hot - perhaps 10 seconds.  Then, heat the contact area on the
battery end while applying solder.  It should melt and flow quite quickly.
As soon as the solder adheres to the battery, remove the heat without
moving anything for a few seconds.  Inspect and test the joint.
A high power soldering iron can also be used.

Here is a novel approach that appears to work:

(From: Clifford Buttschardt (cbuttsch@slonet.org)).

There is really no great amount of danger spot welding tabs!  They usually
are made of pure nickel material.  I put two sharp pointed copper wires in
a soldering gun, place both on the tab in contact with the battery case
and pull the trigger for a short burst.  The battery remains cool.

(From: mcovingt@ai.uga.edu (Michael Covington)).

Of course!  A soldering gun is a source of about 1.5 V at 100 A RMS.
Should make a fine spot-welder.  You should write that up for QST
("Hints and Kinks") or better yet, send it in a letter to the editor
of "Electronics Now" (the magazine I write for).

  10.20) How do those on-battery or on-the-package battery testers work?

There is a graded width resistance element that gets connected when you pinch
those two points.  It heats up - substantially, BTW.  Some sort of liquid
crystal or other heat sensitive material changes from dark to clear or yellow
at a fairly well defined temperature.

Incidentally, since the current is significant, repeated 'testing' will drain
the batteries - as with any proper under-load battery test!  This isn't an
issue for occasional testing but if the kids figure how to do this....

Personally, I would rather use a $3 battery checker instead of paying for
throw-away frills!

  10.21) Battery eliminator for laptop or appliance with dead NiCd

Even where you have the AC adapter, it is quite likely that simply removing
the (shorted) battery pack will not allow you to use it.  This is because
it probably uses the battery as a smoothing capacitor.  You cannot simply
replace the battery with a large electrolytic capacitor because the battery
also limits the voltage to a value determined by the number of cells in the
pack.  Without it, the voltage would be much too high, possibly resulting in
damage.  You could use N power diodes in series (i.e., N=Vb/.7) to drop the
approximate voltage of the battery pack AND a large capacitor but you would be
wasting a lot of power in the form of heat.

One alternative is to substitute a regulated power supply with an output equal
to the the battery voltage and current capacity found by dividing the VA
rating of the normal wall adapter by the battery's nominal terminal voltage
(this will be worst case - actual requirements may be less).  Connect this
directly in place of the original battery pack.  Unless there is some other
sort of interlock, the equipment should be perfectly happy and think it is
operating from battery power!

Also see the chapter: "AC Adapters and Transformers".

Chapter 11) Incandescent Light Bulbs, Lamps, and Lighting Fixtures

Editor's note: More information on incandescent light bulbs can be found
at: http://www.misty.com/~don/.

  11.1) Incandescent light bulbs - single and three way

The basic incandescent lamp operates on the same basic principles as
the original carbon filament lamp developed by Thomas Edison.  However,
several fundamental changes have made it somewhat more efficient and
robust.  However, modern bulbs are hardly efficient at producing lighte.
Typically, only about 3 to 7 percent of the electrical energy used by a
typical incandescent light bulb is turned into useful (visible) light.  The
rest goes to waste (usually) as heat.

Tungsten replaced carbon as the filament material once techniques for
working this very brittle metal were perfected (Edison knew about tungsten
but had no way of forming it into fine wire).  Most light bulbs are now filled
with an inert gas rather than containing a vacuum like Edison's originals.
This serves two purposes: it reduces filament evaporation and thus prolongs
bulb life and reduces bulb blackening and it allows the filament to operate
at a higher temperature and thus improves color and brightness.  However,
the gas conducts heat away so some additional power is wasted to heating
the surroundings.

Incandescent lamps come in all sizes from a fraction of a watt type smaller
than a grain of wheat to a 75 KW monsters bulbs.  In the home, the most common
bulbs for lighting purposes are between 4 W night light bulbs and 250-300 W
torch bulbs (floor standing pole lamps directing light upwards).  For
general use, the 60, 75, and 100 W varieties are most common.  Recently,
55, 70 and 95 W 'energy saving' bulbs have been introduced.  However, these
are just a compromise between slightly reduced energy use and slightly less
light.  My recommendation: use compact fluorescents to save energy if these
fit your needs.  Otherwise, use standard light bulbs.

Most common bases are the Edison medium (the one we all know and love) and
the candelabra (the smaller style for night lights, chandeliers, and wall

Three-way bulbs include two filaments.  The three combinations of which
filaments are powered result in low, medium, and high output.  A typical
3-way bulb might be 50 (1), 100 (2), and 150 (1+2) W.  If either of the
filaments blows out, the other may still be used as a regular bulb.
Unfortunately, 3-way bulbs do tend to be much more expensive than ordinary
light bulbs.  There may be adapters to permit a pair of normal bulbs to
be used in a 3-way socket - assuming the space exists to do this safely
(without scorching the shade).

The base of a 3-way bulb has an additional ring to allow contact to the second
filament.  Inexpensive 3-way sockets (not to be confused with 3-way wall
switches for operation of a built-in fixture from two different locations)
allow any table lamp to use a 3-way bulb.

Flashlight bulbs are a special category which are generally very small
and run on low voltage (1.5-12 V).  They usually have a filament which is
fairly compact, rugged, and accurately positioned to permit the use of a
reflector or lens to focus the light into a fixed or variable width beam.
These usually use a miniature screw or flange type base although many
others are possible.  When replacing a flashlight bulb, you must match
the new bulb to the number and type of battery cells in your flashlight.

Automotive bulbs are another common category which come in a variety of
shapes and styles with one or two filaments.  Most now run on 12 V.

Other common types of incandescent bulbs: colored, tubular, decorative,
indoor and outdoor reflector, appliance, ruggedized, high voltage (130 V).

  11.2) Why do my light bulbs seem to burn out at warp speed?

The lifespan of an average incandescent bulb is 750-1000 hours which is
about 1.5 months if left on continuously or roughly 4 months if used 8 hours
a day.  So, if  you are seeing a 3-4 month lifespan, this may not be that out
of line depending on usage.  With a lot of bulbs in a house, you may just think
you are replacing bulbs quite often.

Having said that, several things can shorted lamp life:

1. Higher than normal voltage - the lifespan decreases drastically for slight
   increases in voltage (though momentary excursions to 125 V, say, should
   not be significant).

2. Vibration - what is the fixture mounted in, under, or on?

3. High temperatures - make sure you are not exceeding the maximum recommended.
   wattage for your fixture(s).

4. Bad switches bad connections due to voltage fluctuations.  If jiggling
   or tapping the switch causes the light to flicker, this is a definite
   possibility.  Repeated thermal shock may weaken and blow the filament.

A bad neutral connection at your electrical service entrance could result
in certain circuits in your house having a higher voltage than normal -
multimeter would quickly identify any.

It may be possible to get your power company to put a recording voltmeter
on your line to see if there are regular extended periods of higher than
normal voltage - above 120 to 125 V.

To confirm that the problem is real, label the light bulbs with their date
(and possibly place of purchase or batch number - bad light bulbs are also
a possibility).  An indelible marker should be satisfactory.

Of course, consider using compact or ordinary fluorescent lamps where
appropriate.  Use higher voltage (130 V) bulbs in hard to reach places.
Bulbs with reinforced filament supports ('tuff bulbs') are also available
where vibration is a problem.

  11.3) Halogen bulbs

(From: Don Klipstein (don@misty.com)).

A halogen bulb is an ordinary incandescent bulb, with a few modifications.
The fill gas includes traces of a halogen, often but not necessarily iodine.
The purpose of this halogen is to return evaporated tungsten to the filament.

As tungsten evaporates from the filament, it usually condenses on the inner
surface of the bulb. The halogen is chemically reactive, and combines with
this tungsten deposit on the glass to produce tungsten halides, which
evaporate fairly easily. When the tungsten halide reaches the filament, the
intense heat of the filament causes the halide to break down, releasing
tungsten back to the filament.

This process, known as the halogen cycle, extends the life of the filament
somewhat. Problems with uneven filament evaporation and uneven deposition of
tungsten onto the filament by the halogen cycle do occur, which limits the
ability of the halogen cycle to prolong the life of the bulb. However, the
halogen cycle keeps the inner surface of the bulb clean. This lets halogen
bulbs stay close to full brightness as they age.  (recall how blackened
an ordinary incandescent bulb can become near the end of its life --- sam).

In order for the halogen cycle to work, the bulb surface must be very hot,
generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may
not adequately vaporize or fail to adequately react with condensed tungsten
if the bulb is too cool. This means that the bulb must be small and made
of either quartz or a high-strength, heat-resistant grade of glass known
as "hard glass".

Since the bulb is small and usually fairly strong, the bulb can be filled
with gas to a higher pressure than usual. This slows down the evaporation
of the filament. In addition, the small size of the bulb sometimes makes it
economical to use premium fill gases such as krypton and xenon instead of
the cheaper argon. The higher pressure and better fill gases can extend
the life of the bulb and/or permit a higher filament temperature that results
in higher efficiency. Any use of premium fill gases also results in less heat
being conducted from the filament by the fill gas, meaning more energy leaves
the filament by radiation, meaning a slight improvement in efficiency.

  11.4) Efficiency, lifetime, and failure modes of halogen bulbs

A halogen bulb is often 10 to 20 percent more efficient than an ordinary
incandescent bulb of similar voltage, wattage, and life expectancy. Halogen
bulbs may also have two to three times as long a lifetime as ordinary bulbs,
sometimes also with an improvement in efficiency of up to 10 percent. How much
the lifetime and efficiency are improved depends largely on whether a premium
fill gas (usually krypton, sometimes xenon) or argon is used.

Halogen bulbs usually fail the same way that ordinary incandescent bulbs
do, usually from melting or breakage of a thin spot in an aging filament.

Thin spots can develop in the filaments of halogen bulbs, since the 
filaments can evaporate unevenly and the halogen cycle does redeposit 
evaporated tungsten in a perfect, even manner nor always in the parts of 
the filament that have evaporated the most.  However, there are additional
failure modes which result in similar kinds of filament degradation.

It is generally not a good idea to touch halogen bulbs, especially the more
compact, hotter-running quartz ones. Organic matter and salts are not good
for hot quartz. Organic matter such as grease can carbonize, leaving a dark
spot that absorbs radiation from the filament and becomes excessively hot.
Salts and alkaline materials (such as ash) can sometimes "leach" into hot
quartz, which typically weakens the quartz, since alkali and alkaline 
earth metal ions are slightly mobile in hot glasses and hot quartz.
Contaminants may also cause hot quartz to crystallize, weakening it. Any of 
these mechanisms can cause the bulb to crack or even violently shatter.
For this reason, halogen bulbs should only be operated within a suitable
fully enclosed fixture.  If a quartz halogen bulb is touched, it should
be cleaned with alcohol to  remove any traces of grease. Traces of salt
will also be removed if the alcohol has some water in it.

  11.5) Use of dimmers with halogen bulbs

Dimming a halogen bulb, like dimming any other incandescent lamp, greatly
slows down the formation of thin spots in the filament due to uneven
filament evaporation. However, "necking" of the ends of the filament remains
a problem. If you dim halogen lamps, you may need "soft-start" devices in
order to achieve a major increase in bulb life.

Another problem with dimming of halogen lamps is the fact that the halogen
cycle works best with the bulb and filament at or near specific optimum
temperatures. If the bulb is dimmed, the halogen may fail to "clean" the
inner surface of the bulb. Or, tungsten halide that results may fail to
return tungsten to the filament.

Halogen bulbs should work normally at voltages as low as 90 percent of
what they were designed for. If the bulb is in an enclosure that conserves
heat and a "soft-start" device is used, it will probably work well at even
lower voltages, such as 80 percent or possibly 70 percent of its rated

Dimmers can be used as soft-start devices to extend the life of any
particular halogen bulbs that usually fail from "necking" of the ends of 
the filament. The bulb can be warmed up over a period of a couple of 
seconds to avoid overheating of the "necked" parts of the filament due to 
the current surge that occurs if full voltage is applied to a cold filament.
Once the bulb survives starting, it is operated at full power or 
whatever power level optimizes the halogen cycle (usually near full power).

The dimmer may be both "soft-starting" the bulb and operating it at slightly
reduced power, a combination that often improves the life of halogen bulbs.
Many dimmers cause some reduction in power to the bulb even when they are set
to maximum.

(A suggestion from someone who starts expensive medical lamps by turning up
a dimmer and reports major success in extending the life of expensive special
bulbs from doing this.)

  11.6) The humorous side of light bulbs

Also see the document: "Engineering, Science, and Other (Pretty Clean) Jokes
Collection" for all the light bulb jokes you could never want.

(From: Susanne Shavelson (shavelson@binah.cc.brandeis.edu)).

People have often mentioned experiencing epidemics of light-bulb-death
after moving into a new (to them) house.  The same thing happened to us
for a few months after moving last year into a 55-year-old house. After
most of the bulbs had been replaced, things settled down. I am persuaded
by the theory advanced by David (?) Owen in his wonderfully informative
and witty book "The Walls Around Us" that houses undergo a sort of nervous
breakdown when a new occupant moves in, leading to all sorts of symptoms
like blown bulbs, plumbing problems, cracks in the walls, and so forth.
Now that the house has become more accustomed to us, the rate at which
strange phenomena are occurring has slowed.

  11.7) Notes on bulb savers

These are usually either Negative Temperature Coefficient (NTC) thermisters
or simple diodes.

When cold, NTC thermisters have a high resistance.  As they warm up, the
resistance decreases so that the current to the light bulb is ramped up
gradually rather than being applied suddenly.

With a properly selected (designed) thermistor, I would not expect the
light output to be affected substantially.  However, while reducing the
power on surge may postpone the death of the bulb, the filament wear
mechanism is due to evaporation and redeposition of the tungsten during
normal operation.  This is mostly a function of the temperature of the

A thermistor which was not of low enough hot resistance would be dissipating
a lot of power - roughly .8 W/volt of drop for a 100W bulb.  Any really
substantial increase in bulb life would have to be due to this drop in voltage
and not the power-on surge reduction.  The bulb saver (and socket) would
also be heating significantly.

The bulb savers that are simply diodes do not have as much of a heat
dissipation problem but reduce the brightness substantially since the
bulbs are running at slightly over half wattage.  Not surprisingly, the
life does increase by quite a bit.  However, they are less efficient at
producing light at the lower wattage and it is more orange. If you are
tempted to then use a higher wattage bulb to compensate, you will
ultimately pay more than enough in additional electricity costs to
make up for the longer lived bulbs.

My recommendation: use high efficiency fluorescents where practical.
Use 130 V incandescents if needed in hard to reach places where bulb
replacement is a pain.  Stay away from bulb savers, green plugs, and
other similar products claiming huge energy reduction.  Your realized savings
for these products will rarely approach the advertised claims and you
risk damage to your appliances with some of these.

  11.8) Can you prove that bulb savers do not work?

No, sorry, I don't have conclusive proof.  I would love to be proved wrong - I
could save a lot on light bulbs.  However, new bulbs do not fail upon
power on.  Old bulbs do.  If you examine the filament of a well worn
light bulb, you will see a very distinct difference in surface appearance
compared to a brand new one.  The surface has gone from smooth to rough.
This change is caused by sustained operation at normal light bulb 
temperatures resulting in unequal evaporation of the filament.

Reducing the power on surge with a thermistor will reduce the mechanical
shock which will postpone the eventual failure.  5X or even 20 % increase
in life is pushing it IMHO.

I do believe that Consumer Reports has tested these bulb savers with
similar conclusions (however, I could be mistaken about the kind of
bulb savers they tested - it was quite awhile ago).

Chapter 12) Fluorescent Lamps, Ballasts, and Fixtures

Editor's note: This section is a condensed version of the document of the
same name available at: http://www.misty.com/~don/.  Special thanks to
Don Klipstein for help in editing of this material.

  12.1) Fluorescent lamp basics

The fluorescent lamp was the first major advance to be a commercial success
in small scale lighting since the tungsten incandescent bulb.  Its greatly
increased efficiency resulted in cool (temperature wise) brightly lit
workplaces (offices and factories) as well as home kitchens and baths.
The development of the mercury vapor high intensity discharge (HID) lamp
actually predates the fluorescent (the latter being introduced commercially
in 1938, four years after the HID).  However, HID type lamps have only
relatively recently become popular in small sizes for task lighting in
the home and office; yard and security area lighting; and light source
applications in overhead, computer, and video projectors.

Fluorescent lamps are a type of gas discharge tube similar to neon signs
and mercury or sodium vapor street or yard lights.  A pair of electrodes,
one at each end - are sealed along with a drop of mercury and some inert
gases (usually argon) at very low pressure inside a glass tube.  The
inside of the tube is coated with a phosphor which produces visible light
when excited with ultra-violet (UV) radiation.  The electrodes are in the
form of filaments which for preheat and rapid or warm start fixtures are
heated during the starting process to decrease the voltage requirements
and remain hot during normal operation as a result of the gas discharge
(bombardment by positive ions).

When the lamp is off, the mercury/gas mixture is non-conductive.  When power
is first applied, a high voltage (several hundred volts) is needed to initiate
the discharge.  However, once this takes place, a much lower voltage -
usually under 100 V is needed to maintain it.

The electric current passing through the low pressure gases (mainly
the mercury vapor) emits quite a bit of UV (but not much visible light).
The internal phosphor coating very efficiently converts most of the UV to
visible light.  The mix of the phosphor(s) is used to tailor the light
spectrum to the intended application.  Thus, there are cool white, warm
white, colored, and black light fluorescent (long wave UV) lamps.  There
are also lamps intended for medical or industrial uses with a special
envelope that passes short wave UV radiation such as quartz.  Some
have an uncoated envelope, and emit short-wave UV mercury radiation.
Others have phosphors that convert shortwave UV to medium wave UV.

CAUTION: many of these emit shortwave or medium wave UV which is
harmful and should not be used without appropriate protection in an
enclosure which prevents the escape of harmful UV radiation.

Fluorescent lamps are about 2-4 times as efficient as incandescent lamps
at producing light at the wavelengths that are useful to humans.  Thus,
they run cooler for the same effective light output.  The bulbs themselves
also last a lot longer - 10,000 to 20,000 hours vs. 1000 hours for a typical
incandescent.  However, for certain types of ballasts, this is only achieved
if the fluorescent lamp is left on for long periods of time without frequent
on-off cycles.

  12.2) Fluorescent lamp labeling

The actual fluorescent tubes are identified by several letters and numbers
and will look something like 'F40CW-T12' or 'FC12-T10'.

So, the typical labeling is of the form FSWWCCC-TDD (variations on this
format are possible):

F  -  Fluorescent lamp.
S  -  Style - no letter indicates normal straight tube; C for Circline.
WW -  Nominal power in Watts.  4, 5, 8, 12, 15, 20, 30, 40, etc.
CCC - Color.  W=White, CW=Cool white, WW=Warm white, BL/BLB=Black light, etc.
T  -  Tubular bulb.
DD -  Diameter of tube in of eighths of an inch.  T8 is 1", T12 is 1.5", etc.

For the most common T12 (1.5 inch) tube, the wattage (except for newer
energy saving types) is usually 5/6 of the length in inches.  Thus, an
F40-T12 tube is 48 inches long.

  12.3) Compact fluorescent bulbs

The compact fluorescent lamp is actually a fairly conventional fluorescent
tube packaged with an integral ballast (either iron or electronic) in
a standard screw base that can be installed into nearly any table lamp
or lighting fixture.

These types are being heavily promoted as energy savings alternatives
to incandescent lamps.  They also have a much longer life - up to 20,000
hours compared to 750 to 1000 hours for a standard incandescent.  While
these basic premises are not in dispute - all is not peaches and cream:

1.  They are often physically larger than the incandescent bulbs they replace
    and simply may not fit the lamp or fixture conveniently or at all.

2.  The funny elongated or circular shape may result in a less optimal
    lighting pattern.

3.  The light is generally cooler - less yellow - than incandescents - this
    may be undesirable and result in less than pleasing contrast with ordinary
    lamps and ceiling fixtures.  Newer models have been addressing this issue.

4.  Some types (usually iron ballasts) may produce an annoying 120 Hz
    (or 100 Hz) flicker.

5.  Ordinary dimmers cannot be used with compact fluorescents.

6.  Like other fluorescents, operation at cold temperatures (under 50 degrees
    F) may be erratic.

7.  There may be am audible buzz from the ballast.

8.  They may produce Radio Frequency Interference (RFI).

9.  The up-front cost is substantial (unless there is a large rebate): $10
    to $20 for a compact fluorescent to replace a 60 W incandescent bulb!

10. Due to the high up-front cost, the pay-back period may approach infinity.

11. While their life may be 20,000 hours, a wayward baseball will break
    one of these $10 to $20 bulbs as easily as a 25 cent incandescent.

Nonetheless, due to the lower energy use and cooler operation, compact
fluorescents do represent a desirable alternative to incandescents.  Just
don't open that investment account for all your increased savings just yet!

  12.4) Fluorescent fixtures

The typical fixture consists of:

* Lamp holder - the most common is designed for the straight bipin base bulb.
  The 12, 15, 24, and 48 inch straight fixtures are common in household and
  office use.  The 4 foot (48") type is probably the most widely used size.
  U shaped, circular (Circline(tm)), and other specialty tubes are also

* Ballast(s) - these are available for either 1 or 2 lamps.  Fixtures with
  4 lamps usually have two ballasts.  See the sections below on ballasts.
  The ballast performs two functions: current limiting and providing the
  starting kick to ionize the gas in the fluorescent tube(s).

* Switch - on/off control unless connected directly to building wiring in
  which case there will be a switch or relay elsewhere.  The power switch
  may have a momentary 'start' position if there is no starter and the
  ballast does not provide this function.

* Starter (preheat fixtures only) - device to initiate the high voltage
  needed for starting.  In other fixture types, the ballast handles this

  12.5) Fluorescent Lamp Ballasts

For a detailed explanation, check your library.  Here is a brief summary.

A ballast serves two functions:

1. Provide the starting kick.
2. Limit the current to the proper value for the tube you are using.

In the old days fluorescent fixtures had a starter or a power switch with
a 'start' position which is in essence a manual starter.  Some cheap ones
still do use this technology.

The starter is a time delay switch which when first powered, allows the
filaments at each end of the tube to warm up and then interrupts this part
of the circuit.  The inductive kick as a result of interrupting the current
through the inductive ballast provides enough voltage to ionize the gas
mixture in the tube and then the current through the tube keeps the
filaments hot - usually.  You will notice that a few iterations are sometimes
needed to get the tube to light.  The starter may keep cycling indefinitely
if either it or one of the tubes is faulty.  While the lamp is on, a
preheat ballast is just an inductor which at 60 Hz (or 50 Hz) has the
appropriate impedance to limit the current to the tube(s) to the proper value.

Ballasts must generally be fairly closely matched to the lamp in terms
tube wattage, length, and diameter.

  12.6) Types of iron ballasts

Instant start, trigger start, rapid start, etc. ballasts include loosely
coupled high voltage windings and other stuff and do away with the starter:

1. The ballast for a preheat fixture (using a starter or power switch with
   a 'start' position) is basically a series inductor.  Interrupting current
   through the inductor provides the starting voltage.

2. The ballast for an instant start fixture has a loosely coupled high
   voltage transformer winding providing about 500-600 V for starting
   in addition to the series inductor.

3. The ballast for a rapid start fixture has in addition small windings for
   heating the filaments reducing the required starting voltage to 250-400 V.
   Trigger start fixtures are similar to rapid start fixtures.

Starting voltage is either provided by the inductive kick upon interruption
of the current bypassed through the starter for (1) or a high voltage winding
in (2) and (3).

In all cases, the current limiting is provided primarily by the impedance
of the series inductance at 60 Hz (or 50 Hz depending on where you live).

  12.7) Electronic ballasts

These devices are basically switching power supplies that eliminate the
large, heavy, 'iron' ballast and replace it with an integrated high frequency
inverter/switcher.  Current limiting is then done by a very small 
inductor, which has sufficient impedance at the high frequency.  Properly
designed electronic ballasts should be very reliable.  Whether they actual
are reliable in practice depends on their location with respect to the heat
produced by the lamps as well as many other factors.  Since these ballasts
include rectification, filtering, and operate the tubes at a high frequency,
they also usually eliminate or greatly reduce the 120 Hz flicker associated
with iron ballasted systems.

I have heard, however, of problems with these relating to radio frequency
interference from the ballasts and tubes.  Other complaints have resulted
do to erratic behavior of electronic equipment using infra red remote controls.
There is a small amount of IR emission from the fluorescent tubes themselves
and this ends up being pulsed at the inverter frequencies which are similar
to those used by IR hand held remote controls.

  12.8) Wiring for preheat fluorescent fixtures

The following is the circuit diagram for a typical preheat lamp - one that
uses a starter or starting switch.

               Power Switch    +-----------+
  Line 1 (H) o------/ ---------|  Ballast  |------------+
                               +-----------+            |
                       .--------------------------.     |
  Line 2 (N) o---------|-       Fluorescent      -|-----+
                       | )         Tube         ( |
                   +---|-         (bipin)        -|-----+
                   |   '--------------------------'     |
                   |                                    |
                   |          +-------------+           |  
                   |          |   Starter   |           |
                   +----------| or starting |-----------+
                              |   switch    |

Here is a variation that some preheat ballasts use.  This type was found on
a F13-T5 lamp fixture:

               Power Switch   +-------------+
  Line 1 (H) o------/ --------|A  Ballast   |
                   +----------|B           C|-----------+
                   |          +-------------+           |
                   |                                    |
                   |   .--------------------------.     |
  Line 2 (N) o-----+---|-       Fluorescent      -|-----+
                       | )         Tube         ( |
                   +---|-         (bipin)        -|-----+
                   |   '--------------------------'     |
                   |                                    |
                   |          +-------------+           |  
                   |          |   Starter   |           |
                   +----------| or starting |-----------+
                              |   switch    |

  12.9) Fluorescent starter operation

The starter incorporates a switch which is normally open.  When power is
applied a glow discharge takes place which heats a bimetal contact.  A second
or so later, the contacts close providing current to the fluorescent filaments.
Since the glow is extinguished, there is no longer any heating of the
bimetal and the contacts open.  The inductive kick generated at the
instant of opening triggers the main discharge in the fluorescent tube.
off with the contacts open.  If the contacts open at a bad time - current
near zero, there isn't enough inductive kick and the process repeats.

Where a manual starting switch is used instead of an automatic starter,
there will be three switch positions:

OFF:   Both switches are open.
ON:    Power switch is closed.
START: (momentary) Power switch remains closed and starting switch in closed.

When released from the start position, the breaking of the filament circuit
results in an inductive kick as with the automatic starter which initiates
the gas discharge.

  12.11) Wiring fluorescent lamps to remote ballasts

For reasonable distances, this should work reliably and be safe provided that:

1. This is only attempted with iron ballasts.  The fire safety and reliability
   of electronic ballasts that are not in close proximity to the lamps is
   unknown.  The ballast may fail catastrophically either immediately or a
   short time later as the circuit may depend on a low impedance (physically
   short) path for stability.

   In addition, there will almost certainly be substantial Radio Frequency
   Interference (RFI) created by the high frequency currents in the long
   wires.  The FCC police (or your neighbors) will come and get you!  This
   may be a problem with iron ballasts as well - but probably of less

2. Wire of adequate rating is used.  The starting voltage may exceed 1 KV.
   Make sure the insulation is rated for at least twice this voltage.  Use
   18 AWG (or heavier) gauge wire.

3. There is no possibility of human contact either when operating or if any
   connectors should accidentally come loose - dangerous line voltage and high
   starting voltage will be present with tubes disconnected.

Note: one application that comes up for this type of remote setup is for
aquarium lighting.  My recommendation would be to think twice about any
homebrew wiring around water.  A GFCI may not help in terms of shock
hazard and/or may nuisance trip due to inductive nature of the ballast
(both depend at least in part on ballast design).

  12.12) Problems with fluorescent lamps and fixtures

In addition to the usual defective or damaged plugs, broken wires in the
cord, general bad connections, fluorescent lamps and fixtures have some
unique problems of their own.  The following assumes a lamp or fixture
with a conventional iron (non-electronic) ballast.  Always try a new set
of fluorescent tubes and starter (where used) before considering other
possible failures.

1. Bad fluorescent tubes.  Unlike incandescent lamps where a visual examination
   of the bulb itself will often identify a broken filament, there is usually
   no way of just looking at a fluorescent tube to determine if it is bad.
   It may look perfectly ok though burned out fluorescents will often have
   one or both ends blackened.  However, a blackened end is not in itself
   an indication of a bad tube.

   Failure of the electrodes/filaments at one or both ends of the the
   fluorescent tube will result in either a low intensity glow or flickering
   behavior.  A broken filament in a fluorescent tube used in a preheat
   type fixture (with a starter) will simply result in a totally dead
   lamp as there will be no power to the starter.  The best approach is
   to simply try replacing any suspect tubes - preferably both in a pair
   that are driven from a single ballast.

2. Bad starter (preheat fixtures only).  The little starter can may go bad
   or be damaged by faulty fluorescent tubes continuously trying to start
   unsuccessfully.  It is a good idea to replace the starter whenever tubes
   are replaced in these types of fixtures.

3. Defective iron ballast.  The ballast may be obviously burned and smelly,
   overheated, or have a loud hum or buzz.  Eventually, a thermal protector
   built into most ballasts will open due to the overheating (though this
   will probably reset when it cools down).  The fixture may appear to be
   dead.  A bad ballast could conceivably damage other parts as well and
   blow the fluorescent tubes.  Ballasts for fixtures less than 30 watts
   usually do not have thermal protection and in rare cases catch fire
   if they overheat.  Defective fixtures should not be left operating.
   If the high voltage windings of rapid start or trigger start ballasts
   are open or shorted, then the lamp will not start.

4. Bad sockets.  These can be damaged through forceful installation or
   removal of a fluorescent tube.  With some ballasts (instant start,
   for example), a switch contact in the socket prevents generation of the
   starting voltage if there is no tube in place.  This minimizes the
   possibility of shock while changing tubes but can also be an additional
   spot for a faulty connection.

5. Lack of ground.  For fluorescent fixtures using rapid start of instant
   start ballasts, it is often necessary for the metal reflector to be
   connected to the electrical system's safety ground.  If this is not
   done, starting may be erratic or may require you to run your hand over
   the tube to get it to light.  In addition, of course, it is an important
   safety requirement.

Warning: electronic ballasts are switching power supplies and need to be
serviced by someone qualified in their repair both for personal safety as
well as continued protection from electrical and fire hazards.

  12.13) Why do fluorescent lamps buzz and what to do about it?

The buzzing light is probably a mundane problem with a defective or cheap
ballast.  There's also the possibility of sloppy mechanical construction
which lets something vibrate from the magnetic field of the ballast until
thermal expansion eventually stops it.

First check for loose or vibrating sheetmetal parts - the ballast may
simply be vibrating these and itself not be defective.

Most newer fixtures are of the 'rapid start' or 'warm start' variety and
do not have starters.  The ballast has a high voltage winding which provides
the starting voltage.

There will always be a ballast - it is necessary to limit the current to the
tube(s) and for starting if there is no starter.  In older fixtures, these will
be big heavy magnetic choke/transformer devices - hard to miss if you
open the thing.  Cheap and/or defective ones tend to make noise.  They
are replaceable but you need to get one of the same type and ratings -
hopefully of higher quality.  A new fixture may be cheaper.

The starter if present is a small cylindrical aluminum can, approximately
3/4" x 1-1/2" in a socket, usually accessible without disassembly.  It
twists counterclockwise to remove.  They are inexpensive but probably not
your problem.  To verify, simply remove the starter after the lamp is on - it
is not needed then.

The newest fixtures may use totally electronic ballasts which are less
likely to buzz.  Warning: electronic ballasts are basically switching
power supplies and are may be hazardous to service (both in terms of
your safety and the risk of a fire hazard from improper repair) unless
you have the appropriate knowledge and experience.

  12.14) Fluorescent lamps cycling on and off

This usually means that the tubes associated with one ballast are cycling
with a period in the 5 to 30 minute range.

There is a thermal protector in the ballast which cuts power to the tubes
that it feeds above a certain temperature.  It is likely that this is causing
the cycling behavior.  The ballast overheats, shuts off, cools down, starts
up, etc.  One or more of the following causes are possible:

* Bad ballast - shorted turns or other fault is causing overheating.

* Bad tubes - replace them and see how it behaves.

* High temperature location - did anything change?  Is it 110 degrees F
  in the shade (or in the room)?

* High line voltage - test with a multimeter.

* Bad starter (preheat fixtures only) - remove the starter with the lights
  on.  If the problem goes away, the starter is probably defective.

* The fixtures are being controlled by a photocell and light from the fixture
  is hitting the sensors and turning them off.

  12.15) Replacing fluorescent lamp or fixture components

Most of these parts are easily replaced and readily available.  However,
it is usually necessary to match the original and replacement fairly
closely.  Ballasts in particular are designed for a particular wattage,
type and size, and tube configuration.  Take the old ballast with you
when shopping for a replacement.  There may be different types of sockets
as well depending on the type of ballast you have.
It is also a possible fire hazard to replace fluorescent tubes with a
different wattage even if they fit physically.  A specific warning has been
issued about replacing 40 W tubes with 34 W energy saving tubes, for example.
The problem is that the ballast must also be correctly sized for the new
tubes and simply replacing the tubes results in excessive current flow and
overheating of the ballast(s).

  12.16) Why are those tiny tiny 4 watt fluorescent bulbs so expensive?

Can you say 'supply and demand' and 'economies of mass production'.  You
are comparing the price of the common F40CW-T12 lamp manufactured by the
zillions and sold in home centers for about $1 with specialty bulbs used
in a relatively few devices like battery powered fluorescent lanterns
and makeup mirrors.  These little bulbs may indeed cost up to ten times
as much as the much larger ones.

By any measure of materials and manufacturing cost, the 4 foot bulb is much
much more expensive to produce.  There is nothing special involved.

Chapter 13) Gas Discharge Lamps

Editor's note: This section is a condensed version of the document of the
same name available at: http://www.misty.com/~don/.  Special thanks to
Don Klipstein for help in editing of this material.

  13.1) Gas discharge lamp basics

Gas discharge lamps are used in virtually all areas of modern lighting
technology including common fluorescent lighting for home and office - and
LCD backlights for laptop computers, high intensity discharge lamps for
very efficient area lighting, neon and other miniature indicator lamps,
germicidal and tanning lamps, neon signs, photographic electronic flashes
and strobes, arc lamps for industry and A/V projectors, and many more.

Unlike incandescent lamps, gas discharge lamps have no filament and do not
produce light as a result of something getting hot (though heat may be
a byproduct).  Rather, the atoms or molecules of the gas inside a glass,
quartz, or translucent ceramic tube, are ionized by an electric current
through the gas or a radio frequency or microwave field in proximity to
the tube.  This results in the generation of light - usually either visible
or ultraviolet (UV).  The color depends on both the mixture of gasses or
other materials inside the tube as well as the pressure and type and amount
of the electric current or RF power.

Fluorescent lamps are a special class of gas discharge lamps where the
electric current produces mostly invisible UV light which is turned into
visible light by a special phosphor coating on the interior of the tube.
See the chapter: "Fluorescent Lamps, Ballasts, and Fixtures".

The remainder of this chapter discusses two classes of gas discharge lamps:
low pressure 'neon' tubes used in signs and displays and high intensity
discharge lamps used for very efficient area and directional lighting.  An
entire chapter is dedicated to "Fluorescent Lamps, Ballasts and Fixtures".

  13.2) Neon lights and signs

Neon technology has been around for many years providing the distinctive
bright glowing signs of commerce of all kinds before the use of colored
plastics became commonplace.

Neon tubes have electrodes sealed in at each end.  For use in signs, they
are formed using the glass blower's skill in the shape of letters, words,
or graphics.  Black paint is used to block off areas to be dark.  They are
evacuated, backfilled, heated (bombarded - usually by a discharge through
the tube at a very high current) to drive off any impurities, evacuated
and then backfilled with a variety of low pressure gasses.

Neon is the most widely known with its characteristic red-orange glow.
Neon may be combined with an internal phosphor coating (like a
fluorescent tube) to utilize neon's weak short-wave UV emissions.
Other gas fills may also be used as well as colored glass or coatings
for added flexibility in determining the tube's color.

  13.3) Power supplies for neon

Extremely high voltage power supplies are used to power neon signs.  In
the past, this was most often provided by a special current limited HV
line transformer called a neon sign or luminous tube transformer.  The
output is typically 6,000 to 15,000 VAC at 15 to 60 mA.  One such unit
can power 10s of feet of tubing.  This transformer acts as its own ballast
providing the high voltage needed for starting and limiting the running
current as well.  Warning: the output of these transformers can be lethal
since even the limited current availability is relatively high.

As with everything else, the newest neon sign power supplies use an
electronic AC-AC inverter greatly reducing the size and weight (and
presumably cost as well) of these power supplies by eliminating the
large heavy iron transformer.

Small neon lamps inside high-tech phones and such also use solid state
inverters to provide the more modest voltage required for these devices.

  13.4) Problems with neon

These fall into two categories:

1. Power supply - like fluorescent ballasts, the high voltage transformers
   can fail resulting in reduced (and inadequate) voltage or no power at all.
   Since they are already current limited, overheating may not result and
   any fuse or circuit breaker may be unaffected.  The use of a proper (for
   safety if nothing else) high voltage meter can easily identify a bad

2. Neon tubes - these may lose their ability to sustain a stable discharge
   over time as a result of contamination, gas leakage, or electrode damage
   (either from normal wear or due to excessive current).  Check for obvious
   damage such as a cracked tube or cracked seals around the electrodes or
   badly deteriorated electrodes.  A previously working tube that now will
   not strike or maintain a stable discharge on a known good transformer 
   will need to be replaced or rebuilt.

  13.5) High intensity discharge (HID) lamp technology

These have been used for a long time in street, stadium, and factory lighting.
More recently, smaller sizes have become available for home yard and crime
prevention applications.  Like other gas discharge lamps, these types
require s special fixture and ballast for each type and wattage.  Unlike
fluorescents, however, they also require a warmup period.

There are three popular types:

* High pressure mercury vapor lamps contain an internal arc tube made of
  quartz enclosed in an outer glass envelope.  A small amount of metallic
  (liquid) mercury is sealed in an argon gas fill inside the quartz tube.
  After the warmup period, the arc emits both visible and invisible (UV)
  light.  High pressure mercury vapor lamps (without color correction)
  produce a blue-white light directly from their discharge arc.  Phosphors
  similar to those used for fluorescent lamps can be used to give these a
  color closer to natural light.  (Without this color correction, people
  tend to look like cadavers).  Mercury vapor lamps have the longest life
  of this class of bulbs - 10,000 to 24,000 hours.  The technology was first
  introduced in 1934 and was the first of the commercially viable HID lamps.

* Metal halide lamps are constructed along similar lines to mercury vapor
  lamps.  However, in addition to the mercury and argon, various metal
  halides are included in the gas fill - usually combinations of sodium iodide
  and scandium iodide.  The use of these compounds increases the luminous
  efficiency and results in a more pleasing color balance than the raw arc
  of the mercury vapor lamp.  Thus, no phosphor is needed to produce a color
  approaching that of a cool white fluorescent lamp.

* High pressure sodium vapor lamps contain an internal arc tube made of
  a translucent ceramic material (a form of aluminum oxide known as
  "polcyrystalline alumina").  Glass and quartz cannot be used since they
  cannot maintain structural strength at the high temperatures (up to 1300
  degrees C) encountered here, and hot sodium chemically attacks quartz
  and glass.  Like other HID lamps, the arc tube is enclosed in an outer
  glass envelope.  A small amount of metallic (solid) sodium in addition
  to mercury is sealed in a xenon gas fill inside the ceramic arc tube.
  Some versions of this lamp use a neon-argon mixture instead of xenon.
  Basic operation is otherwise similar to mercury or metal halide lamps.
  High pressure sodium vapor lamps produce an orange-white light and have
  a luminous efficiency much higher than mercury or metal halide lamps.

Unlike fluorescent lamps, HID lamps will give full light output over a
wide range of temperatures.  This often makes HID lamps more suitable than
fluorescent lamps for outdoor use.

When cold, the metallic mercury or sodium in the arc tube is in its normal
state (liquid or solid) at room temperature.  During the starting process,
a low pressure discharge is established in the gases.  This produces very
little light but heats the metal contained inside the arc tube and gradually
vaporizes it.  As this happens, the pressure increases and light starts being
produced by the discharge through the high pressure metal vapor. A quite
noticeable transition period occurs when the light output increases
dramatically over a period of a minute or more.  The entire warmup process
may require up to 10 minutes, but typically takes 3 to 5 minutes.  A hot
lamp cannot be restarted until it has cooled since the voltage needed to
restrike the arc is too high for the normal AC line/ballast combination to

  13.6) Problems with high intensity discharge lamps

While HID lamps have a very long life compared to incandescents (up to
24,000 hours), they do fail.  The ballasts can also go bad.  In addition,
their light output falls off gradually as they age.  For some types, light
output may drop to half its original value towards the end of their life.

A lamp which is cycling - starting, warming up, then turning itself off -
is probably overheating due to a bad bulb or ballast.  A thermal protector
is probably shutting down the fixture to protect it or the arc is being
extinguished on its own.  However, make sure that it is not something
trivial like a photoelectric switch that is seeing the light from the lamp
reflected from a white wall or fence and turning the fixture off once the
(reflected) light intensity becomes great enough!

Sodium lamps often "cycle" when they have aged greatly.  The arc tube's
discolorations absorb light from the arc, causing the arc tube to overheat,
the sodium vapor pressure becomes excessive, and the arc cannot be maintained.
If a sodium lamp "cycles", the first suspect is an aging bulb which should be

If you have more than one fixture which uses **identical** bulbs, swapping
the bulbs should be the first test.  If the problem remains with the fixture,
then its ballast or other circuitry is probably bad.  Don't be tempted to swap
bulbs between non-identical fixtures even if they fit unless the bulb types
are the same.

Warning: do not operate an HID lamp if the outer glass envelope is cracked
or broken.  First, this is dangerous because the extremely hot arc tube can
quite literally explode with unfortunate consequences.  In addition, the
mercury arc produces substantial amounts of short wave UV which is extremely
hazardous to anything living.  The outer glass normally blocks most of
this from escaping.  Some lamps are actually designed with fusable links
that will open after some specified number of hours should air enter the
outer envelope.  Thus, an undetected breakage will result in the lamp dying
on its own relatively quickly.

Chapter 14) Motors 101

  14.1) Small motors in consumer electronic equipment

A large part of the functionality of modern appliances is based on the
use of motors of one form or another.  They are used to rotate, blow,
suck, sweep, spin, cut, grind, shred, saw, sand, drill, plane, time,
and control.

Motors come in all shapes and sizes but most found in small appliances
can be classified into 5 groups:

1. Universal motors - run on AC or DC, speed may be varied easily.  Quite
   efficient but use carbon brushes and may require maintenance.

2. Single phase induction motors - AC, fairly fixed speed except by switching,
   windings, very quiet.  Quite efficient and low maintenance.

3. Shaded pole induction motors - AC, somewhat fixed speed, very quiet, not
   very efficient and low maintenance.

4. Small permanent magnet DC motors - DC, variable or constant speed, often
   cheaply made, fairly quiet, prone to problems with metal brushes.

5. DC brushless motors - DC usually, somewhat variable or fixed speed, very
   quiet, low maintenance.

6. Synchronous timing motors - constant speed absolutely tied to power line.
   The long term accuracy of clocks based on the AC line exceed that of most
   quartz oscillator based time pieces since the ultimate reference is an
   atomic frequency standard.

Each has its advantages and disadvantages.  More than one type may be suitable
for any particular application.

  14.2) Identifying type of unknown motor

Determining the actual type of motor is the first step toward being
able to test to see if it is being powered properly or if there is
a fault in the motor itself.

Open frame motors in line operated appliances with a single coil off to
one side are almost always shaded pole induction motors.  To confirm, look
for the copper 'shading rings' embedded in the core.  There will usually
be either 1 or 2 pairs of these.  Their direction is determine by the
orientation of the stator frame (position of the shading rings).

For enclosed motors, first check to see if there are carbon brushes on
either side of a commutator made of multiple copper bars.  If so, this
is almost certainly a series wound 'universal' motor that will run on
AC or DC though some may be designed for DC operation only.

If there are no brushes, then it is likely a split phase induction or
synchronous motor.  If there is a capacitor connected to the motor, this
is probably used for starting and to increase torque when running.

Where there is a capacitor, it is likely that how this is wired to the
motor determines the direction of rotation - make sure you label the

Very small motors with enclosed gear reducers are usually of the synchronous
type running off the AC line.  Their direction of rotation is often set by
a mechanical one-way clutch mechanism inside the casing.

Motors used in battery operated tools and appliances will usually be of
the permanent magnet DC type similar to those found in toys and electronic
equipment like VCRs and CD players.  Most of these are quite small but there
are exceptions - some electric lawnmowers use large versions of this type of
motor, for example.  These will be almost totally sealed with a pair of
connections at one end.  Direction is determined by the polarity of the
DC applied to the motor.

For universal and DC permanent magnet motors, speed control may be accomplished
with an internal mechanical governor or electronic circuitry internal or
external to the motor.  On devices like blenders where a range of (useless)
speeds is required, there will be external switches selecting connections
to a tapped winding as well as possibly additional electronic circuitry.  The
'solid state' design so touted by the marketing blurb may be just a single
diode!  A similar approach may also be used to control the speed of certain
types of induction motors (e.g., ceiling fans) but most are essentially fixed
speed devices.

Once identified, refer to the appropriate section for your motor.

COLIN Electric Motor Service has a page with some Motor Connection Diagrams
for large motors that may be of some value (though more so if you have a few'
100 horsepower three-phase motors in your concrete processing plant!).

  14.3) Universal motors

The Universal motor is the most common type of high speed motor found
in appliances and portable line operated power tools.  Typical uses
include vacuum cleaners, floor polishers, electric drills, routers, and
sewing machines.  They are likely to be found anywhere medium power, high
speed, and/or variable speed control are required capabilities.  Note that
quiet operation is NOT a feature of these motors.  Therefore, they will
not often be found in electronic equipment.

Construction consists of a stationary set of coils and magnetic core called the
'stator' and a rotating set of coils and magnetic core called the 'armature'.
Incorporated on the armature is a rotating switch called a 'commutator'.
Connection to the armature is via carbon (or metal) contacts called 'brushes'
which are mounted on the frame of the motor and press against the commutator.
Technically, these are actually series wound DC motors but through the use of
steel laminated magnetic core material, will run on AC or DC - thus the name

Speed control of universal motors is easily achieved with thyristor
based controllers similar to light dimmers.  However, simply using a
light dimmer as a motor speed controller may not work due to the
inductive characteristics of universal motors.

Changing direction requires interchanging the two connections between the
stator and the armature.

This type of motor is found in blenders, food mixers, vacuum cleaners,
sewing machines, and many portable power tools.

  14.4) Problems with universal motors

These motors can fail in a number of ways:

* Open  windings - this may result in a bad spot, a totally dead motor,
  lack of power, or excessive sparking. 

* Shorted windings - this may result in excessive current, severe sparking,
  reduced speed and power, and overheating.  The thermal protector, fuse,
  or circuit breaker may trip.  Continuing to run such a motor may result
  in a meltdown or burned coils and insulation - i.e., a burned out motor.

* Worn carbon brushes - while these usually last for the life of the
  appliance, this is not always the case.  The result could be erratic
  or sluggish operation, excessive sparking, or even damage to the

* Dry/worn bearings - this may result in a tight or frozen motor or a motor
  shaft with excessive runout.  The result may be a spine tingling squeal
  during operation and/or reduced speed and power, and overheating.  Running
  such a motor may eventually lead to burnout due to overheating from the
  increased load.

  14.5) Testing of universal motors

Test the field coils for continuity with an ohmmeter.  An open winding is
bad and will require replacement of the entire stator assembly unless the
break can be located.  Compare the resistance of the two windings - they
should be nearly equal.  If they are not, a short in one of the windings
is likely.  Again, replacement will be necessary.

Also test for a short to the frame - this should read infinity.  If lower than
1 M or so, the motor will need to be replaced unless you can locate the fault.

An open or shorted armature winding may result in a 'bad spot' - a position
at which the motor may get stuck.  Rotate the motor by hand a quarter turn and
try it again.  If it runs now either for a fraction of a turn or behaves
normally, then replacement will probably be needed since it will get stuck
at the same point at some point in the future.  Check it with an ohmmeter.
There should be a periodic variation in resistance as the rotor is turned
having several cycles per revolution determined by the number of commutator
segments used.  Any extremely low reading may indicate a shorted winding.
Any erratic readings may indicate the need for brush replacement or cleaning.
An unusually high reading may indicate an open winding or dirty commutator.
Cleaning may help a motor with an open or short or dead spot.

A motor can be tested for basic functionality by disconnecting it from the
appliance circuit and running it directly from the AC line (assuming it is
intended for 115 VAC operation - check to be sure).

CAUTION: series wound motors can overspeed if run without a load of any kind
and spectacular failure may result due to centrifugal disassembly of the
armature due to excess G forces.  In other words, the rotor explodes.  This is
unlikely with these small motors but running only with the normal load
attached is a generally prudent idea.

  14.6) About commutators and brushes in universal motors

A commutator is essentially a rotating switch which routes power to the
appropriate windings on the armature so that the interaction of the fixed
(stator) and rotating (armature) magnetic fields always results in a
rotational torque.  Power is transferred to the commutator using carbon
brushes in most motors of this type.  The carbon is actually in the form
of graphite which is very slippery as well.  Despite that fact that graphite
is a relatively soft material, a thin layer of graphite is worn off almost
immediately as the motor is started for the first time and coats the
commutator.  After this, there is virtually no wear and a typical set of
carbon brushes can last thousands of hours - usually for the life of the
appliance or power tool.

A spring presses the brush against the rotating commutator to assure good
electrical contact at all times.  A flexible copper braid is often embedded
in the graphite block to provide a low resistance path for the electric
current.  However, small motors may just depend on the mounting or pressure
spring to provide a low enough resistance.

The typical universal motor will have between 3 and 12 armature windings
which usually means a similar number of commutator segments.  The segments
are copper strips secured in a non-conductive mounting.  There are supposed
to be insulating gaps between the strips which should undercut the copper.
With long use, the copper may wear or crud may build up to the point that
the gaps between the copper segments are no longer undercut.  If this
happens, their insulating properties will largely be lost resulting in an
unhappy motor.  There may be excessive sparking, overheating, a burning
smell, loss of power, or other symptoms.

Whenever checking a motor with a commutator, inspect to determine if the
commutator is in good condition - smooth, clean, and adequately undercut.
Use a narrow strip of wood or cardboard to clean out the gaps assuming
they are still present.  For larger motors, a hacksaw blade can be used
to provide additional undercutting if needed though this will be tough
with very small ones.  Don't go too far as the strength of the commutator's
mounting will be reduced.  About 1/32 to 1/16 inch should do it.  If the
copper is pitted or worn unevenly, use some extra fine sandpaper (600 grit,
not emery cloth or steel wool which may leave conductive particles behind)
against the commutator to smooth it while rotating the armature by hand.

Since the carbon brushes transmit power to the rotating armature,
they must be long enough and have enough spring force behind them to
provide adequate and consistent contact.  If they are too short, they
may be unstable in their holders as well - even to the point of being
ripped from the holder by the commutator causing additional damage.

Inspect the carbon brushes for wear and free movement within their holders.
Take care not to interchange the two brushes or even rotate them from their
original orientation as the motor may then require a break-in period and
additional brush wear and significant sparking may occur during this time.
Clean the brushes and holders and/or replace the brushes if they are broken
or excessively worn.

  14.7) Repairing small universal motors

Too bad that the Sears lifetime warranty only applies to hand (non-power)
tools, huh?

Which part of the motor is bad?  The armature or stator?  How do you 
know? (A smelly charred mess would probably be a reasonable answer).

Rewinding a motor is probably going to way too expensive for a small
appliance or power tool.  Finding a replacement may be possible since
those sizes and mounting configurations were and are very common.

However, I have, for example, replaced cheap sleeve bearings with ball
bearings on a couple of Craftsman power drills.  They run a whole lot
smoother and quieter.  The next model up used ball bearings and shared
the same mounting as the cheaper sleeve bearings so substitution was

  14.8) Single phase induction motors

Where a fixed speed is acceptable or required, the single phase induction
motor is often an ideal choice.  It is of simple construction and very
robust and reliable.  In fact, there is usually only one moving part which
is a solid mass of metal.

Most of the following description applies to all the common types of
induction motors found in the house including the larger fractional
horsepower variety used in washing machines, dryers, and bench power

Construction consists of a stationary pair of coils and magnetic core called
the 'stator' and a rotating structure called the 'rotor'.  The rotor is
actually a solid hunk of steel laminations with copper or aluminum bars running
lengthwise embedded in it and shorted together at the ends by thick plates.
If the steel were to be removed, the appearance would be that of a 'squirrel
cage' - the type of wheel used to exercise pet hamsters.  A common name for
these (and others with similar construction) are squirrel case induction

These are normally called single phase because they run off of a single
phase AC line.  However, at least for starting and often for running as
well, a capacitor or simply the design of the winding resistance and
inductance, creates the second (split) phase needed to provide the rotating
magnetic field.

For starting, the two sets of coils in the stator (starting and running
windings) are provided with AC current that is out of phase so that the
magnetic field in one peaks at a later time than the other.  The net
effect is to produce a rotating magnetic field which drags the rotor
along with it.   Once up to speed, only a single winding is needed though
higher peak torque will result if both windings are active at all times.

Small induction motors will generally keep both winding active but larger
motors will use a centrifugally operated switch to cut off the starting
winding at about 75% of rated speed (for fixed speed motors).  This is
because the starting winding is often not rated for continuous duty

For example, a capacitor run type induction motor would be wired as shown
below.  Interchanging the connections to either winding will reverse the
direction of rotation.  The capacitor value is typical of that used with
a modest size fan motor.

      Hot o------+------------+
                 |             )||
                 |             )|| Main winding
                 |           2 )||
  Neutral o---+---------------+ 
              |  |
              |  |    C1     3         C1: 10 uF, 150 VAC
              |  +----||------+
              |                )||
              |                )|| Phase winding
              |              4 )||

Speed control of single phase induction motors is more complex than
for universal motors.  Dual speed motors are possible by selecting
the wiring of the stator windings but continuous speed control is 
usually not provided.  This situation is changing, however, as the
sophisticated variable speed electronic drives suitable for induction
motors come down in price.

Direction is determined by the relative phase of the voltage applied
to the starting and running windings (at startup only if the starting
winding is switched out at full speed).  If the startup winding is
disconnected (or bad), the motor will start in whichever direction
the shaft is turned by hand.

This type of motor is found in larger fans and blowers and other
fixed speed appliances like some pumps, floor polishers, stationary
power tools, and washing machines and dryers.

  14.9) Shaded pole induction motors

These are a special case of single phase induction motors where only a
single stator winding is present and the required rotating magnetic field is
accomplished by the use of 'shading' rings which are installed on the stator.
These are made of copper and effectively delay the magnetic field buildup in
their vicinity just enough to provide some starting torque.

Direction is fixed by the position of the shading rings and electronic
reversal is not possible.  It may be possible to disassemble the motor
and flip the stator to reverse direction should the need ever arise.

Speed with no load is essentially fixed but there is considerable
reduction as load is increased.  In many cases, a variable AC source
can be used to effect speed control without damaging heating at any speed.

This type of motor is found in small fans and all kinds of other low
power applications like electric pencil sharpeners where constant speed
is not important.  Compared to other types of induction motors, efficiency
is quite poor.

  14.10) Problems with induction motors

Since their construction is so simple and quite robust, there is little
to go bad.  Many of these - particularly the shaded pole variety - are even
protected from burnout if the motor should stall - something gets caught in
a fan or the bearings seize up, for example.

Check for free rotation, measure voltage across the motor to make sure it
is powered, remove any load to assure that an excessive load is not the

If an induction motor (non-shaded pole) won't start, give it a little help
by hand.  If it now starts and continues to run, there is a problem with
one of the windings or the capacitor (if used).

For all types we have:

* Dirty, dry, gummed up, or worn bearings - if operation is sluggish even
  with the load removed, disassemble, clean, and lubricate with electric
  motor oil.  The plain bearings commonly used often have a wad of felt
  for holding oil.  A add just enough so that this is saturated but not
  dripping.  If there is none, put a couple of drops of oil in the bearing

* Open coil winding - test across the motor terminals with your ohmmeter.
  A reading of infinity means that there is a break somewhere - sometimes
  it is at one end of the coil and accessible for repair.  For those with
  starting and running windings, check both of these.

* Shorted coil winding - this will result in loss of power, speed, and
  overheating.  In extreme cases, the motor may burn out (with associated
  smelly byproducts) or blow a fuse.  The only way to easily test for a winding
  that is shorted to itself is to compare it with one from an indentical good
  motor and even in this case, a short which is only a few turns will not show
  up (but will still result in an overheating motor).

* Coil shorted to the frame - this will result in excessive current, loss of
  power, overheating, smoke, fire, tripped breaker or overload protector, etc.

If any of these faults are present, the motor will need to be replaced (or
rewound if economical - usually not for typical appliance motors).  The only
exception would be if the location of the open or short is visible and can be
repaired.  They usually are not.

For capacitor run type:

* A bad capacitor may be the cause of a motor which will not start, has
  limited power, excessive hum, or overheats.  A simple test with your
  ohmmeter on the high resistance scale can give some indication of whether
  the capacitor is good.  remove at least one lead of the capacitor and
  measure across it.  A good capacitor will show an initially low reading
  which will quickly climb to infinity.  If there is no low reading at all
  or it remains low, then the capacitor is bad (open or shorted respectively).
  This does not really prove the capacitor is good but if the test shows open
  shorted, it is definitely bad.  Substitution is best.

For larger induction motors with centrifugal starting switches:

* A centrifugal switch which does not activate the starting winding will
  result in a motor that will not start on its own but will run if it is
  rotated initially by hand.  A centrifugal switch that does not cut off
  when the motor is up to speed will result in excessive power use,
  overheating, and may blow a line fuse or trip a circuit breaker.  These
  are usually pretty simple and a visual inspection (may require disassembly)
  should reveal broken, worn, or otherwise defective parts.  Check for
  proper switch contact closing and opening with a continuity tester or
  ohmmeter.  Inspect the rotating weights, springs, and the sliding lever
  for damage.

* Bad rotor - this is somewhat rare but repeated heating and cooling
  cycles or abuse during starting can eventually loosen up the (supposedly)
  welded connections of the copper bars to the end rings.  The result is
  a motor that may not start or loses power since the required shorted
  squirrel cage has been compromised.  One indication of this would be
  a rotor that is asymmetric - it vibrates or has torque at only certain
  large angular positions indicating that some of the bars are not connected
  properly.  Normally, an induction motor rotor is perfectly symmetric.

  14.11) Disassembling and reassembling a universal or induction motor

The description below assumes that the construction is of an enclosure
with an integral stator and brush holder.  For those with an internal
structural frame, remove the outer casing first.

For the case of induction motors, ignore any comments about brushes as
there are none.  With shaded pole motors, the entire assembly is often
not totally enclosed with just stamped sheet metal brackets holding the

Follow these steps to minimize your use of 4 letter expletives:

1. Remove the load - fan blades, gears, pulleys, etc.  If possible, label
   and disconnect the power wiring as well as the motor can them be totally
   removed to the convenience of your workbench.

2. Remove the brushes if possible.  Note the location of each brush and
   its orientation as well to minimize break-in wear when reinstalled.  Where
   the brushes are not easily removable from the outside, they will pop
   free as the armature is withdrawn.  Try to anticipate this in step (6).
   (Universal motors only).

3. Confirm that there are no burrs on the shaft(s) due to the set screw(s)
   that may have been there.  For motors with plain bearings in particular,
   these will need to be removed to allow the shaft(s) to be pulled out
   without damage to the bushing.  For ball bearing motors, the bearings
   will normally stay attached to the shaft as it is removed.

4. Use a scribe or indelible pen to put alignment marks on the covers so that
   they can be reassembled in exactly the same orientation.

5. Unscrew the nuts or bolts that hold the end plates or end bells together
   and set these aside.

6. Use a soft mallet if necessary to gently tap apart the two halves or end
   bells of the motor until they can be separated by hand.

7. Remove the end plate or end bell on the non-power shaft end (or the end
   of your choice if they both have extended shafts).

8. Remove the end plate or end bell on the power (long shaft) end.  For
   plain bearings, gently ease it off.  If there is any resistance, double
   check for burrs on the shaft and remove as needed so as not to damage
   the soft bushing.

9. Identify any flat washers or spacers that may be present on the shaft(s) or
   stuck to the bushings or bearings.  Mark down their **exact** location and
   orientation so that they may be replaced during reassembly.  Clean these
   and set aside.

Inspect all components for physical damage or evidence of overheating or
burning.  Bad bearings may result in very obvious wear of the shaft or
bushings or show evidence of the rotor scraping on the stator core.
Extended overloads, a worn commutator, or shorted windings may result in
visible or olfactory detected deterioration of wire insulation.

While it is apart, brush or blow out any built up dust and dirt and thoroughly
clean the shaft, bushings, commutator, and starting switch (present in large
induction motors, only).

Relubrication using electric motor oil for plain bearings and light grease
for non-sealed ball/roller bearings.

CAUTION: cleanliness is absolutely critical when repacking bearings or else
you will be doing this again very soon.

Badly worn ball bearings will need replacement.  However, this may be better
left to a motor rebuilding shop as they are generally press fit and difficult
to remove and install.

Reassemble in reverse order.  If installation of the brushes needs to be
done before inserting the armature, you will need to feed them in spring
end first and hold them in place to prevent damage to the fragile carbon.
Tighten the nuts or bolts evenly and securely but do not overtighten.

  14.12) Determining wiring for multispeed induction motor

Many motors have a wiring diagram on their nameplate.  However, where this is
not the case, some educated guessing and experimentation will be necessary.

Here is an example for a common multispeed furnace blower motor.  In this
case there is no capacitor and thus there are few unknowns.

" Here's the problem - I have a squirrel cage fan that I would like to wire
  up. Unfortunately, there's only these four wires hanging there and I would
  hate to burn it up trying combinations.  Here's what I know:

  * The motor came out of a furnace.
  * It's marked with three amp ratings (4.5, 6.1, 7.5) - three speeds, right?
  * The wires look like they were white, black, red and blue.

  * With a ohm meter set on 200, I tried the following combinations:

              White   Black   Blue   Red
      White    0      1.5     2.2    2.9
      Black    1.5    0        .7    1.3
      Blue     2.2     .7     0       .7
      Red      2.9    1.3      .7    0

 So, how do I connect the motor?"

From the resistance readings, it would appear that the Black, Blue, and Red
are all taps on a single winding. My guess (and there are no warranties :-)
would be: White is common, black is HIGH, blue is MEDIUM, red is LOW.

I would test as follows:

Put a load in series with the line.  Try a 250 W light bulb.  This should
prevent damage to the motor if your connections are not quite correct.

Connect each combination of White and one other color.  Start with black.
It should start turning - not nearly at full speed, however.  If it does
turn, then you are probably safe in removing the light bulb.

Alternatively, if you have a Variac (variable autotransformer) of sufficient
ratings, just bring up the voltage slowly.

If it does not make any effort to start turning - just hums, go to plan B.
It may require a starting/running capacitor and/or not be a 3 speed motor.

  14.13) Small permanent magnet DC motors

These are constructed like small versions of universal motors except that the
stator field is provided by powerful ceramic permanent magnets instead of a
set of coils.  Because of this, they will only operate on DC as direction is
determined by the polarity of the input voltage.

Small PM DC motors are used in battery or AC adapter operated shavers,
electric knives, and cordless power tools.

Similar motors are also used in cassette decks and boomboxes, answering
machines, motorized toys, CD players and CDROM drives, and VCRs.  Where
speed is critical, these may include an internal mechanical governor or
electronic regulator.  In some cases there will be an auxiliary tachometer
winding for speed control feedback.  This precision is rarely needed for

As noted, direction is determined by the polarity of the input power
and they will generally work equally well in either direction.

Speed is determined by input voltage and load.  Therefore, variable
speed and torque is easily provided by either just controlling the
voltage or more efficiently by controlling the duty cycle through pulse
width modulation (PWM).

These motors are usually quite reliable but can develop shorted or open
windings, a dirty commutator, gummed up lubrication, or dry or worn bearings.
Replacement is best but mechanical repair (lubrication, cleaning) is
sometimes possible.

  14.14) Problems with small PM motors

These motors can fail in a number of ways:

* Open or shorted windings - this may result in a bad spot, excess
  current drain and overheating, or a totally dead motor. 

* Partial short caused by dirt/muck, metal particle, or carbon buildup on
  commutator - this is a common problem in CD player spindle and cassette
  deck motors but not as common a problem with typical appliances.

* Dry/worn bearings - this may result in a tight or frozen motor or a motor
  shaft with excessive runout.  The result may be a spine tingling squeal
  during operation and/or reduced speed and power.

  14.15) Testing of small PM motors

An open or shorted winding may result in a 'bad spot' - a position at which
the motor may get stuck.  Rotate the motor by hand a quarter turn and
try it again.  If it runs now either for a fraction of a turn or behaves
normally, then replacement will probably be needed since it will get stuck
at the same point at some point in the future.

Check across the motor terminals with an ohmmeter.  There should be a periodic
variation in resistance as the rotor is turned having several cycles per
revolution determined by the number of commutator segments used.  Any
extremely low reading may indicate a shorted winding. An unusually high
reading may indicate an open winding or dirty commutator.  Cleaning may help
a motor with an open or short or dead spot as noted below.  Erratic readings
may indicate the need for cleaning as well.

Also check between each terminal and the case - the reading should be high,
greater than 1M ohm.  A low reading indicates a short.  The motor may still
work when removed from the equipment but depending on what the case is
connected to, may result in overheating, loss of power, or damage to the
driving circuits when mounted (and connected) to the chassis.

A motor can be tested for basic functionality by disconnecting it from the
appliance circuit and powering it from a DC voltage source like a couple
of 1.5 V D Alkaline cells in series or a DC wall adapter or model train power
pack.  You should be able to determine the the required voltage based on the
battery or AC adapter rating of the appliance.  If you know that the appliance
power supply is working, you can use this as well.

  14.16) Identifying voltage and current ratings small PM motors

If the carcass of the device or appliance is still available, the expected
voltage may be determined by examining the original power supply - batteries,
voltage regulator, wall adapter, etc.

The following applies to the common DC permanent magnet (PM) motors found
in tape players and cassette decks used for the capstan.

* This motor may have an internal speed regulator.  In that case, you can
  determine the appropriate voltage by using a variable supply and increasing
  it slowly until the speed does not increase anymore.  This will typically
  be between 2 and 12 V depending on model.  The motor should then run
  happily up to perhaps 50% more input voltage than this value.

  Note that many motors are actually marked with voltage and current ratings.
  Internal regulators may be electronic or mechanical (governor).  One way to
  tell if there is an internal electronic regulator is to measure the
  resistance of the motor.  If it is more than 50 ohms and/or is different
  depending on which direction the meter leads are connected, then there is
  an electronic regulator.

Motors without internal speed regulators are used for many functions in
consumer electronics as well as toys and small appliances.

* If it does not have an internal regulator, typical supply voltages are
  between 1.5 and 12 V with typical (stopped) winding resistances of 10 to 50
  ohms.  Current will depend on input voltage, speed, and load.  It *cannot*
  be determined simply using Ohms law from the measured resistance as the
  back EMF while running will reduce the current below what such a calculation
  would indicate.

The wire color code will probably be red (or warm color) for the positive (+)
lead and black (or dark cool) color for the minus (-) lead.

  14.17) Reviving a partially shorted or erratic PM motor

Dirt or grime on the commutator can result in intermittent contact and erratic
operation.  Carbon or metal particle buildup can partially short the motor
making it impossible for the controller to provide enough voltage to maintain
desired speed.  Sometimes, a quick squirt of degreaser through the ventilation
holes at the connection end will blow out the shorting material.  Too much will
ruin the motor, but it would need replacement otherwise anyway.  This has
worked on Pioneer PDM series spindle motors.

Another technique is to disconnect the motor completely from the circuit
and power it for a few seconds in each direction from a 9 V or so DC source.
This may blow out the crud.  The long term reliability of both of these
approaches is unknown.

WARNING: Never attempt to power a motor with an external battery or power
supply when the motor is attached to the appliance, particularly if it
contains any electronic circuitry as this can blow electronic components
and complicate your problems.

It is sometimes possible to disassemble the motor and clean it more
thoroughly but this is a painstaking task best avoided if possible.
See the section: "Disassembling and reassembling a miniature PM motor".

  14.18) Disassembling and reassembling a miniature PM motor

Note: for motors with carbon brushes, refer to the section: "Disassembling
and reassembling a universal or induction motor".  This procedure below is
for those tiny PM motors with metal brushes.

Unless you really like to work on really tiny things, you might want to just
punt and buy a replacement.  This may be the strategy with the best long
term reliability in any case.  However, if you like a challenge, read on.

CAUTION: disassembly without of this type should never be attempted with high
quality servo motors as removing the armature from the motor may partially
demagnetize the permanent magnets resulting in decreased torque and the need
to replace the motor.  However, it is safe for the typical small PM motor
found in appliances and power tools.

Select a clean work area - the permanent magnets in the motor will attract
all kinds of ferrous particles which are then very difficult to remove.

Follow these steps to minimize your use of 4 letter expletives:

1. Remove the load - fan blades, gears, pulleys, etc.  Label and disconnect
   the power wiring as well as the motor will be a whole lot easier to work
   on if not attached to the appliance or power tool.  Note: polarity is
   critical - take note of the wire colors or orientation of the motor if
   it is directly soldered to a circuit board!

2. Confirm that there are no burrs on the shaft(s) due to the set screw(s)
   that may have been there.  For motors with plain bearings in particular,
   these will need to be removed to allow the shaft(s) to be pulled out
   without damage to the bushing.

3. Use a scribe or indelible pen to put alignment marks on the cover so that
   it can be replaced in the same orientation.

4. Make yourself a brush spreader.  Most of these motors have a pair of
   elongated holes in the cover where the power wires are connected to
   the commutator.  These allow the very delicate and fragile metal brushes
   to be spread apart as the armature is removed or installed.  Otherwise,
   the brushes will get hung up and bent.  I have found that a paper clip
   can be bent so that its two ends fit into these holes and when rotated
   will safely lift the brushes out of harm's way.

5. Use a sharp tool like an awl or dental pick to bend out the 2 or 3 tabs
   holding the cover in place.

6. Insert the brush spreader, spread the brushes, and pull the cover off of
   the motor.  If done carefully, no damage will be done to the metal brushes.

7. The armature can now be pulled free of the case and magnets.

8. Identify any flat washers or spacers that may be present on the shaft(s).
   Mark down their **exact** location and orientation so that they may be
   replaced during reassembly.  Clean these and set aside.

Inspect all components for physical damage or evidence of overheating or
burning.  Bad bearings may result in very obvious wear of the shaft or
bushings or show evidence of the rotor scraping on the stator core.
Extended overloads, a worn commutator, or shorted windings may result in
visible or olfactory detected deterioration of wire insulation.

Check that the gaps in the commutator segments are free of metal particles
or carbonized crud.  Use a sharp instrument like an Xacto knife blade to
carefully clear between the segments.  Clean the brushes (gentle!), shafts,
and bushings.

When reassembling, make sure to use your brush spreader when installing the

  14.19) DC brushless motors

These are a variation on the small DC motors described above and uses a
rotating permanent magnet and stationary coils which are controlled by
some electronic circuitry to switch the current to the field magnets at
exactly the right time.  Since there are no sliding brushes, these are
very reliable.

DC brushless motors may be of ordinary shape or low profile - so called 
pancake' style.  While not that common in appliances yet, they may be found
in small fans and are used in many types of A/V and computer equipment (HD,
FD, and CD drives, for example).  Fortunately, they are extremely reliable.
However, any non-mechanical failures are difficult to diagnose.  In some
cases, electronic component malfunction can be identified and remedied.
Not that common in appliances but this is changing as the technology matures.

Direction may be reversible electronically (capstan motors in VCR require
this, for example).  However, the common DC operated fan is not reversible.

Speed may be varied over a fairly wide range by adjusting the input
voltage on some or by direct digital control of the internal motor drive

The most common use for these in appliances are as small cooling fans
though more sophisticated versions are used as servo motors in VCRs and
cassette decks, turntables, and other precision equipment.

  14.20) Disassembling and reassembling a DC brushless fan

This is the type you are likely to encounter - modify this procedure for
other types.

1. Remove the fan from the equipment, label and disconnect the power wires
   if possible.

2. Remove the manufacturer's label and/or pop the protective plastic button
   in the center of the blade assembly.  Set these aside.

3. You will see an E-clip or C-clip holding the shaft in place.  This must
   be removed - the proper tool is best but with care, a pair of fine
   needlenose pliers, narrow screwdriver, dental pick, or some other
   similar pointy object should work.  Take great care to prevent it from
   going zing across the room.

4. Remove the washers and spacers you find on the shaft.  Mark down their
   positions so that they can be restored exactly the way you found them.

5. Withdraw the rotor and blades from the stator.

6. Remove the washers and spacers you find on the shaft or stuck to
   the bushings.  Mark down their positions so that they can be restored
   exactly the way you found them.

For fans with plain bearings, inspect and clean the shaft and the hole in the
bushing using a Q-tip and alcohol or WD40 (see there is a use for WD40!).
Check for any damage.  Lubricate with a couple drops of electric motor oil
in the bushing and any felt pads or washers.

For fans with ball bearings, check the bearings for free rotation and runout
(that they do not wobble or wiggle excessively).  If bad, replacement will
be needed, though this may not be worth the trouble.  These are generally
sealed bearings so lubrication is difficult in any case.  On the other hand,
they don't go bad very often.

Reassemble in reverse order.

  14.21) Synchronous timing motors

Miniature synchronous motors are used in mechanical clock drives as found
in older clock radios or electric clocks powered from the AC line,
appliance controllers, and refrigerator defrost timers.  These assemblies
include a gear train either sealed inside the motor or external to it.
If the motor does not start up, it is probably due to dried gummed up
lubrication.  Getting inside can be a joy but it is usually possible to
pop the cover and get at the rotor shaft (which is usually where the
lubrication is needed).  However, the tiny pinion gear may need to be
removed to get at both ends of the rotor shaft and bearings.

These consist of a stator coil and a magnetic core with many poles and a
permanent magnet for the rotor.  (In many ways, these are very similar to
stepper motors).  The number of poles determines the speed precisely and
it is not easily changed.

Direction is sometimes determined mechanically by only permitting the motor
to start in the desired direction - they will usually be happy to start either
way but a mechanical clutch prevents this (make note of exactly how is was
positioned when disassembling).  Direction can be reversed in this manner
but I know of no actual applications where it would be desirable.  Others
use shading rings like those in a shaded pole induction motor to determine
the direction of starting.

Speed, as noted, is fixed by construction and for 60 Hz power it is
precisely equal to: 7200/(# poles) RPM.  Thus, a motor with 8 poles
will run at 900 RPM.

  14.22) Disassembling and reassembling a small timing motor

The best approach is usually replacement.  In some designs, just the rotor
and gear unit can be replaced while retaining the stator and coils.

However, if your motor does not start on its own, is sluggish, or squeals,
cleaning and lubrication may be all that is needed.  However, to get to the
rotor bearing requires removal of the cover and in most cases the rotor as
well.  This may mean popping off a press-fit pinion gear.

1. Remove the motor from the appliance and disconnect its power wires if
   possible.  This will make it a lot easier to work on.

2. Remove the cover.  This may require bending some tabs and breaking an
   Epoxy seal in some cases.

3. Inspect the gears and shafts for gummed up lubrication.  Since these
   motors have such low torque, the critical bearing is probably one for
   the main rotor.  If there is any detectable stiffness, cleaning and
   lubrication is called for.

4. You can try lubricating in-place but this will usually not work as there
   is no access to the far bearing (at the other end of the shaft from the
   pinion gear).  I have used a small nail or awl to pop the pinion gear
   from the shaft by gently tapping in the middle with a small hammer.

5. Withdraw the rotor from the motor.

6. Identify any flat washers or spacers that may be present on the shaft.
   Mark down their **exact** location and orientation so that they may be
   replaced during reassembly.  Clean these and set aside.
Inspect and clean the shaft and bushings.  Lubricate with electric motor oil.

Reinstall the rotor and washers or spacers.  Then press the pinion gear back
onto the shaft just far enough to allow a still detectable end-play of about
.25 to .5 mm.  Check for free rotation of the rotor and all gears.  Replace
the cover and seal with household cement once proper operation has been

  14.23) Motor bearing problems

A dry or worn bearing can make the motor too difficult to turn properly or
introduce unacceptable wobble (runout) into the shaft as it rotates.

Feel and listen for a dry bearing:

The shaft may be difficult to turn or it may turn with uneven torque.
A motor with a worn or dry bearing may make a spine tingling high pitched
sound when it is turning under power.  A drop of light machine oil (e.g.
electric motor oil) may cure a dry noisy bearing - at least temporarily.

Runout - wobble from side to side - of a motor shaft is rarely critical
in a small appliance but excessive side-to-side play may result in
noise, rapid bearing wear, and ultimate failure.

  14.24) Motor noise

If the noise is related to the rotating motor shaft, try lubricating the motor
(or other suspect) bearings - a single drop of electric motor oil, sewing
machine oil, or other light oil (NOT WD40 - it is not a suitable lubricant),
to the bearings (at each end for the motor).  This may help at least as a
temporary fix.  In some cases, using a slightly heavier oil will help with
a worn bearing.  See the section: "Lubrication of appliances and electronic

For AC motors in particular, steel laminations or the motor's mounting
may be loose resulting in a buzz or hum.  Tightening a screw or two
may quiet it down.  Painting the laminations with varnish suitable for
electrical equipment may be needed in extreme cases.  Sometimes, the
noise may actually be a result of a nearby metal shield or other
chassis hardware that is being vibrated by the motor's magnetic field.
A strategically placed shim or piece of masking tape may work wonders.

  14.25) Finding a replacement motor

In many cases, motors are fairly standardized and you may be able
to find a generic replacement much more cheaply than the original
manufacturer's part.  However, the replacement must match the following:

1. Mechanical - you must be able to mount it.  In most cases, this
   really does mean an exact drop-in.  Sometimes, a slightly longer
   shaft or mounting hole out of place can be tolerated.  The pulley
   or other drive bushing, if any, must be able to be mounted on the new
   motor's shaft.  If this is a press fit on the old motor, take extreme
   care so as not to damage this part when removing it (even if this means
   destroying the old motor in the process - it is garbage anyway).

2. Electrical - the voltage and current ratings must be similar.

3. Rotation direction - with conventional DC motors, this may be
   reversible by changing polarity of the voltage source.  With AC motors,
   turning the stator around with respect to the rotor will reverse rotation
   direction.  However, some motors have a fixed direction of rotation
   which cannot be altered.

4. Speed - depending on the type appliance, this may or may not be that
   critical.  Most induction motors run at slightly under 900, 1800, or 3600
   RPM (U.S., 60 Hz power).  DC motor speed can vary quite a bit and these
   are rarely marked.

MCM Electronics, Dalbani, and Premium Parts stock a variety of small DC
replacement motors.  Appliance repair shops and distributors may have
generic replacements for larger motors.  Junk and salvage yard or your
local dump may actually have what you want for pennies on the pound or less!

  14.26) Is motor rebuilding economical?

So you left your electric cement mixer mixing away and forgot about it - for
3 days.  Now the motor is a black charred ruin.  You can rent a jack hammer
to break up the cement but the motor is a lost cause.  The manufacturer has
been out of business for 20 years.  What should you do besides give the tool
a decent burial?

Here is a possible option for, in this case, a planer:

(From: Ed Schmitt (easchmitt@penn.com)).

I located a person who rewinds motors and had the job done for $60.00.
That was over 7 years ago, and the planer is still working.  Look around
and find some of our elderly craftsman who know how to rewind motors.
You'll save a bundle, and have a working tool.

(From: Michael Sloane (msloane@worldnet.att.net)).

That is an interesting thought - I have a 1942 Cat road grader with burned
out wiring in the 6 V wiper motor. Cat wants $200(!) for a new one, so I
would like to find someone who would rewind the old one (and make it
12 V at the same time).  I wouldn't even bother with the so-called
auto-electric guys, all they do is replace the brushes and diodes on
starters and alternators.

  14.27) Motor armature testing - or - what is a growler?

A common fault that cannot always be reliably identified with a simple
ohmmeter test is a couple of shorted turns in the winding that do not
affect the total resistance significantly.

A growler is basically an AC electromagnet exciting the windings in the
armature.  A shorted armature winding will act as a the secondary of a
transformer resulting in a high current flow and high induced magnetic field.

Hold a piece of spring steel like a hacksaw blade as a probe over the armature
as you rotate it slowly on the electromagnet.  A shorted winding will show up
as a strong audible vibration of the 'probe' - thus the name growler.

  14.28) Small motor repair and replacement

(From: mjsrnec (mjsrnec@prairie.lakes.com)).

Most motor shops won't bother with the universal motors because they are much
cheaper to replace than repair. However, if yours is a special be prepared to
pay standard rates for the service.  Email the Electrical Apparatus Service
Association found at: http://www.easa.com/  to find the EASA shop nearest you.

If you think the motor may be fairly common pick up a Grainger catalog or go
to: Grainger or: Grainger Universal Motor Index.

If this is for a power tool, contact the tool manufacturer for the authorized
service center nearest your location.

Chapter 15) Large Appliances

Editor's note:  Yes, I know this is supposed to be the "Small Appliance FAQ"
but so be it.  Until and if I write a "Large Appliance FAQ", this will have
to do :-).

  15.1) Web sites for large appliance troubleshooting

The following has complete diagnostic references for many major brands of
dishwashers, gas and electric driers, gas and electric ranges and ovens,
refrigerators, and washing machines:

* A-1 Appliance Parts - RepairNet Online Diagnostics

Here are some other sites with large appliance DIY repair info:

* Appliance Clinic
* Appliance Repair Net
* Garrell's Appliance Center

Also see "Sam's Neat, Nifty, and Handy Bookmarks" for additional large
appliance related Web sites.

  15.2) Electric oven calibration

If your cakes come out all drippy or your chicken breasts end up hard as a
rock and charred, this discussion is for you!  It is possible that the
thermostat on your oven needs calibration.  However, major errors in
temperature may be the result of a bad heating element, blown fuse or
tripped breaker, a door that doesn't close or seal properly, etc.  Confirm
that the oven is in otherwise good operating condition before attempting

The procedure given below assumes that your oven has a mechanical thermostat
which is still the most common type.  For an electronic thermostat - one in
which the set-point is entered via a touchpad - the adjustment (if any) will
likely be on the controller circuit board rather than under the temperature
knob.  If you do attempt calibration of an electronic thermostat, make double
sure that you have located the correct adjustment screw!

(Portions from: ken859@sprynet.com).

Most thermostats have a calibration screw located under the knob.  Try pulling
the knob off and look at the shaft.  Some shafts have a small screw located
in the center.  Rotating this screw will change the trip point at which the
thermostat will turn on and off.  This is determined by the sensor located
inside the oven itself.

You can also have your oven calibrated by an appliance service technician
by locating them in your yellow pages and have him/her make a house call but
you wouldn't be reading this if you wanted someone else to do it!

The following procedure can be performed by almost anyone who knows which end
of a screwdriver to poke into the screw head :-).

1.  Locate 2 thermometers that are oven safe and place them inside the oven
    on a shelf approximately in the center of the oven.  Make sure the actual
    sensing elements of the thermometers do not touch anything.

2.  Remove the knob from the thermostat and locate an appropriate screwdriver
    for the adjusting screw.  Re-install the knob.

3.  Turn on the oven and set it for 300 degrees F.  Allow it to come up to
    temperature (set light goes out).  Then wait an additional 10 minutes.

4.  Look at the temperature of the thermometers (averaging the two) and
    determine the error amount and direction.  Note: if the error is large
    (greater than, perhaps, 50 degrees F) then there may be a problem with
    the oven (such as a bad temperature sensor) which will not be remedied
    by calibration.

5.  Remove the knob and adjust the screw in the shaft one way or the other
    depending on which way the oven set-point is off.  If the direction is
    not marked to increase or decrease the temperature, just pick one - there
    is no standard.  You may be wrong on the first attempt :-(.

    Note: Rotate the adjustment in small increments!

6.  Place the knob back on the shaft. 

7.  Again wait 10 minutes after the oven set light goes off.  

8.  Look at the temperature of the thermometers and see how far off the error
    is now.  

9.  Repeat the steps above until this set-point is accurate.

10. Now set the thermostat to 400 degrees F and repeat the steps above for
    this setting.

11. The oven set-point should now be a lot closer to the actual temperature.

If you really want to be the oven to be accurate,  Turn the oven off and allow
it to completely cool.  The, repeat the above complete procedure 2 more times
or until the accuracy you desire is achieved.

Repeating this procedure may seem redundant but some thermostats because of
their mechanical nature have a margin of error.  Also due to the mechanical
nature, some settling of the parts inside does occur.

As long as the heating elements in the oven do not fail.  The oven should
maintain its accuracy for quite some time.  A simple check of the oven
once every 6 months or once every year will assure you that your baking
temperatures will be accurate.

  15.3) Heat control in electric range surface units

The typical electric range surface unit has two spiral elements.  In
older ranges, they are used in various combinations across the 120 and
240.  We have a GE range like this which has 5 heat settings (and off)
for each 'burner'.

Given 2 element and 2 voltages there are 8 possible connection
possibilities.  I don't know which 5 my GE range uses.

Newer ranges use a single element or just parallel the two elements and
use variable power control (pulse width modulation or thyristor phase
control) to obtain arbitrary heat levels and/or a thermostat to sense
the actual temperature.

BTW, this GE range is about 46 years old and still going strong (except
for the 1 hour timer which died about 5 years ago.)

(The following experiments from: Mark Zenier (mzenier@netcom.com)).

From my multiple renovations of my mother's stove of a similar vintage:

Warm is 120 volts applied to both elements of a burner in series.

Low is 120 volts applied to one of the two elements.  The burners are
wired so that they are not the same.  Half of the burners used the
center element, the others used the rim element.  Usually split between
front burners and rear.  (This is a GE, other companies used two
interleaved spiral elements.)

Third is 120 volts applied to both elements.

Second is 240 volts applied to one element, like Low, it varies 
from burner to burner.

High is 240 volts applied to both elements.

  15.4) Electric range top element does not work properly

If all the elements are dead, check for blown fuses/tripped circuit breakers.
There may be some in the range unit itself in addition to your electrical
service panel.

If one element is completely dead on all heat settings, the control is
probably bad or there is a broken wire.  If it is stuck on high for
all control settings or is erratic, the control is bad - replacements
are readily available and easily installed.

On ranges with push button heat selection, a pair of heating elements are
switched in various combinations across 120 and/or 240.  If some heat
settings do not work, the most likely cause is that one of the heatings
elements is burnt out although a bad switch is also possible.  Kill power
to the range and test the heating elements for continuity.  Replacements
are available from appliance parts stores or the places listed in the section:
"Parts suppliers".

  15.5) Improvised welding repair of heating elements

Due to the high temperatures at which they operate, welding may provide
better long term reliability of heating elements than mechanical fasteners.
However, in most cases, the following extreme measures are not really needed.

Warning: only consider the following if you are absolutely sure you understand
the safety implications of working directly with line voltage - it is not very
forgiving.  There is both an electrocution and fire hazard involved.

(From: Donald Borowski (borowski@spk.hp.com)).

I have had some success with welding heating element wires back together.
I did this on two toasters recently.

I extracted the carbon rod from a carbon/zinc D cell ('Classic' or 'Heavy
Duty' variety, alkalines do hot have carbon rods).  I filed one end to a point.

I wired a circuit as follows:

* Hot side of line to one connection of 1500 electric heater.

* Other connection of heater to carbon rod.

* Both connections of toaster under repair to neutral side of line, toaster
  turned on (to make connection).

* I twisted together the heater wires to be welded.

Then I touched the carbon rod to the wires, and drew it away.

There was a very brief arc, but it seemed to be sufficient.  It did take
several tries to get it right.

Of course, all safety warnings apply:  Dangerous power line voltages, welder's
mask needed for protect eyes, possible dangerous chemicals in D cell, etc.

This should work for other types of Nichrome coiled or ribbon heating elements
as well.

I vaguely recall seeing many years ago a suggestion of making a paste of
borax and putting it over the twisted-together ends.  I guess it was supposed
to act as a self-welding flux.  Anyone else recall this?

  15.6) Range, oven, and furnace electronic ignition

Many modern gas stoves, ovens, furnaces, and other similar appliances use an
electronic ignition rather than a continuously burning pilot flame to ignite
the fuel.  These are actually simple high voltage pulse generators.

* Where starting is manual (there is a 'start' position on the control(s), a
  set of switch contacts on the control(s) provides power to the ignition

  - A problem of no spark with only one control indicates that the fault is
    with it or its wiring.

  - A problem with continuous sparking even with all the controls off or in
    their normal positions indicates a short - either due to a defective switch
    in one of the controls or contamination bypassing the switch contacts.

* Where starting is automatic, an electronic sensor, thermocouple, or bimetal
  switch provides power to the ignition module as needed.

The Harper-Wyman Model 6520 Kool Lite(tm) module is typical of those found in
Jenne-Aire and similar cook-tops.  Input is 115 VAC, 4 mA, 50/60 Hz AC.  C1
and D1 form a half wave doubler resulting in 60 Hz pulses with a peak of about
300 V and at point A and charges C2 to about 300 V through D2.  R2, C3, and
DL1 form a relaxation oscillator triggering SCR1 to dump the charge built up
on C2 into T1 with a repetition rate of about 2 Hz.

           C1                A       D1                     T1 o
    H o----||----------------+-------|>|-------+-------+       +-----o HVP+
         .1 uF     D2 1N4007 |     1N4007      |       |  o ||( 
         250 V   +----|>|----+                 |       +--+ ||(
                 |           |                 |           )||(
                 +---/\/\----+                 |       #20 )||( 1:35
                 |  R1 1M    |             C2 _|_          )||(
                 |        R2 /           1 uF ---      +--+ ||(
                 |       18M \    DL1   400 V  |     __|__  ||(
                 |           /    NE-2         |     _\_/_     +-----o HVP-
                 |           |    +--+         |     / |
                 |           +----|oo|----+---------'  | SCR1
                 |       C3  |    +--+    |    |       | S316A
                 |  .047 uF _|_        R3 /    |       | 400 V
                 |    250 V ---       180 \    |       | 1 A
                 |           |            /    |       |
         R4 2.7K |           |            |    |       |
    N o---/\/\---+-----------+------------+----+-------+

Before you blame the ignition module for either lack of spark or continuous
spark, make sure the wiring is in good condition and completely dry and clean
(well reasonably clean!).  Confirm that proper voltage is reaching the module
with a multimeter or neon test lamp.  The modules are actually quite robust:

* Any liquid that may have dripped into the module may result in temporary or
  permanent failure.  Fortunately, as with the model cited above, it may be
  possible to pop off the bottom cover (with power OFF or the module removed!)
  and clean it.  The most likely failure would be the SCR if you are into
  component level repair.  Else, just replace it.

  WARNING: There are several capacitors inside that may be charged to as much
  as 300 volts.  The charge they can hold is probably not dangerous but may be
  painful or startling.  Discharge these before touching anything inside or
  attempting to check components.  Use a screwdriver blade or test clips and
  then confirm that they are discharged with your multimeter.

* Contamination of the controls from spilled liquid (did your tea kettle boil
  over?) may result in continuous activation of the ignition module since any
  electrical leakage across the switch contacts will likely be enough to
  activate it - only a few mA are required.  Remove the control panel cover
  and dry it out or unplug the range or oven for a couple of days.  If the
  contamination is not just plain water, it is a good idea to clean it
  thoroughly to prevent future problems.

* Spills into the area of the electrodes at the gas burner assembly may short
  out the ignition for ALL the burners since they probably use the same module.
  Again, clean and dry it out or let it dry out on its own (if just water).

These are probably standard modules and replacements should be available from
your local appliance repair shop or parts supplier.  An exact mechanical match
is not needed as long as the specifications are compatible.

  15.7) Replacing a thermostat

The following applies to refrigerators and freezers, air conditioners,
electric space heaters, as well as other small appliances.

Removing the thermostat (unplug AC line first!) and cleaning the contacts
using contact cleaner NOT sandpaper or a file - may help temporarily.
Replacement is easy if the cold control is self contained using a bimetal
strip.  If it uses a liquid filled bulb, the tube may snake around inside
the cabinet and may be more challenging. Still no big deal.  An appliance
part distributor or your appliance manufacturer should have a replacement.

  15.8) Oven door seal repair

(From: Brian Symons (brians@mackay.net.au)).

If you need a high temp silastic (e.g., for refitting glass windows in ovens)
then the Black silastic sold for car windscreen sealing from the local service
station or garage is the stuff.  Works well.  Someone here waited several
months and paid $80 for what he could buy down the road for $10 - it was even
the same brand.

  15.9) Freezer is normal but fresh food compartment isn't even cool

Some possibilities:

* The door is not properly closing for some reason.

* Someone messed with the controls accidentally.

* Something is blocking the passageway between the evaporator and the 
  fresh food compartment.

* The defrost cycle is not working and ice has built up in the evaporator
  coils.  This could be due to a bad defrost timer (most likely), bad
  defrost heater, or bad defrost thermostat.

* The interior light is not going out when the door is closed - that small
  amount of heat can really mess up the temperature (remove the bulb(s) as a
  test if you are not sure.

* Low Freon can result in problems of this type but that is a lot less likely.
  (These refrigeration systems are hermetically sealed (welded).  Slow leaks
  are unlikely.)

If you are handy, you can narrow down the problem and possible fix it - a
defrost timer can be easily replaced.  See the section: "Defrost system
operation and wiring".

  15.10) Refrigerator not cooling after a week

First, clean the condensor coils.  It is amazing how much dust collects there
and interferes with proper cooling.

If you just turned it on a week ago and it is not acting up, a failure of
the defrost timer is quite likely.  On an old fridge, the grease inside
dries out/gunks up and restarting from cold results in it not running.
It takes about a week for enough ice to build up to be a problem.

This is a $12 repair if you do it yourself or $100 or so if you call someone.

Could be other things but that is what I would check first.  On a GE, it is
usually located at the bottom front and there is a hole in the front in which
you can poke your finger to turn it clockwise by hand.  Turn it until you 
hear a click and the fridge shuts off.  You should not get melting in the
evaporator compartment and water draining into the pan at the bottom.  The
fridge compressor should start up again in 10-20 minutes but I bet in your
case it won't as the timer needs replacement.

  15.11) Defrost system operation and wiring

The most common type of defrost system on a no-frost refrigerator or freezer
usually consists of:

* Defrost timer - motor driven (typically) switch which selects between the
  compressor and its associated devices (like the evaporator fan) and the
  defrost heater (located adjacent to the evaporator coils).  The timer motor
  likely only runs when the main thermostat calls for cooling.

* Defrost heater - resistance element located in the evaporator compartment to
  melt ice built up on the coils

* Defrost thermostat - closed when the temperature is below about 32 degrees F
  to allow current to flow to the defrost heater.  Shuts off once the ice melts
  as indicated by the temperature rising above 32 degrees F.

Testing: It should be possible to easily identify the bad components.  For
the following, it is assumed that the main thermostat is set such that the
compressor is on.

* Usually, it is possible to manually turn the defrost timer shaft (through
  a hole in the timer case) with a finger or small screwdriver - try both
  directions - one should rotate easily with a slight ratcheting sound until
  a distinct 'click' is heard.

* The click indicates that the switch has changed position.  The compressor
  should shut off (or start up if it was stuck in defrost).  Over 90% of the
  rotation range enables the compressor with a short time (e.g., 20 minutes)
  for defrost.  The total time is several hours (6 typical).

* At this point, the defrost heater should come on if there is enough ice to
  keep the defrost thermostat below 32 F.  You will know it comes on because
  there will be crackling sounds as ice melts and parts expand and the element
  may even glow red/orange when hot.  Water should start flowing to the drip
  pan.  If there is no sign of heating:

  - Test (with power off) the resistance of the element - it should measure
    under 100 ohms (31 ohms typical).

    If open - at the terminals of the element - it is bad.

  - Test (with power applied) for AC voltage across the element.  If there is
    none, test across the defrost thermostat - there should be none.  Or, test
    across the series combination of the defrost heater and thermostat.
    There should be full line voltage across the series combination.

    If there is still none, the contacts on the defrost timer may be bad, you
    may be in the normal cycle by mistake, the main thermostat may be defective
    or not calling for cooling, the wiring may be incorrect or have bad
    connections, or there may be no power to the outlet.

    If there is voltage across the defrost thermostat, it is defective or
    the temperature is above 32 F.  Confirm by jumpering across the defrost
    thermostat and see if the defrost heater comes on.

* If ice buildup is modest, the defrost thermostat should shut off the heater
  in a few minutes.  In any case, the timer should advance and switch to the
  normal position with the compressor running and defrost heater shut off in
  about 10 to 20 minutes.

  If the timer never advances, the motor is likely not running due to gummed
  up lubrication, a broken or loose gear, or a broken wire.  On some of these
  timers, the connections to the motor are to the moving contacts and break
  after a few years.  These can be repaired by soldering them to a more stable

  One indication that the motor is not being powered is for it to be ice cold
  even after several hours with the compressor (and thus the timer) being on.
  Normally, the coil runs warm to hot.  If the timer never advances even with
  a toasty winding, the lubrication is gummed up or a gear has broken.

Defrost timers are readily available at appliance parts distributors.  A
generic timer will cost about $12.  An exact replacement, perhaps up to $35.
If you call in a service person, expect to pay over $100 for the part and

Generally, the defrost timer is an SPDT switch operated by a cam on a small
motor with a 4 to 8 hour cycle (depending on model).  For an exact replacement,
just move the wires from the old timer to the same terminals on the new unit.
For a generic replacement, the terminal location may differ.  Knowing what is
inside should enable you to determine the corresponding terminal locations
with a multimeter.

The terminal numbering and wire color code for the defrost timer in a typical
GE refrigerator is shown below:

                     Black (4)
    Gray (3)      /o---------o Normal position - Compressor, evaporator fan.
H* o-----+------/
         |         o---o Blue (2)
       Timer           |         Defrost heater  Defrost Thermostat
       Motor (3180     o------------/\/\/\------------o/o----------+
         |    ohms)                 31 ohms          32 F          |
         |                                                         |
         | Orange (1)                                              |
         o---------------------------------------------------------+--o Common

   * H is the Hot wire after passing through the main thermostat (cold control)
     in the fresh food compartment.

  15.12) Compressor starting relays

Most refrigeration compressors use a current mode relay to engage the
starting winding of their split phase induction motor.  However, a
PTC (Positive Temperature Coefficient) thermistor might also be used.

A starting relay senses the current flowing to the run winding of the
compressor motor (the coil is a few turns of heavy wire in series with
the run winding) and engages the starting winding when that current is
above a threshold - indicating that the rotor is not up to speed.

A PTC thermistor starts with a very low resistance which increases to
a high value when hot.  Proper operation depends on the compressor getting
up to speed within a specific amount of time.

For testing only, you can substitute an external switch for the starting
device and try to start it manually.

CAUTION: Do not bypass a faulty starting device permanently as the starting
winding is not intended to run continuously and will overheat and possibly
burn out if left in the circuit.

Assuming you have waited long enough for any pressures to equalize (five
minutes should do it if the system was operating unless there is some
blockage - dirt or ice - inside the sealed system), you can test for proper
operation by monitoring the voltage on the start and run windings of the
compressor motor.  If there is line voltage on both windings and it still
does not start up - the overload protector switches off or a fuse or circuit
breaker pops - the compressor is likely bad.

  15.13) Changing the temperature range of a small refrigerator

It is simple in principle.  The cold control - the thing with the knob -
needs to be modified or replaced.  It is a simple on/off thermostat. 
You may be able to figure out how to adjust its limits (mechanical) or
simply locate a suitable thermostat and install it in place of the
existing unit.  Note: if it uses a capillary tube to a sensing bulb, don't
attempt to modify that part - it is sealed and should remain that way.
The mechanism it operates may still be adjustable.  However, you will
likely loose the low end of your temperature range.

  15.14) Washer sometimes spins

When it should be spinning, is the motor running?  Does it complete the
cycle in the normal time?

I would guess that the solenoid to shift it into spin is binding or
erratic.  Thus opening the door gives switches it on and off like the
timer but since it sometimes works, it sometimes works by cycling the
door switch.

  15.15) Clothes washer does not fill (cold or hot)

This assumes the unit has power and otherwise operates normally.  However,
determining this may be difficult if the completion of the cycle is dependent
on a water weight or volume sensor.

There are several possibilities:

1. The appropriate water inlet filter is clogged.  This will be accessible by
   unscrewing the hose connection.  Clean it.

2. The solenoid is bad.  If you are electrically inclined, put a multimeter
   on the cold water valve to see if it is getting power.

3. The temperature selector switch is bad or has bad connections.

4. The controller is not providing the power to the solenoid (even
   for only hot or cold, these will have separate contacts).

  15.16) Window air conditioner preventive maintenance

Very little needs to be done to get many years of service from a typical
window air conditioner.

Of course, clean the inside filter regularly.  This is usually very easy
requiring little or no disassembly (see your users manual).  Some slide
out without even removing the front cover (e.g., Emerson Quiet Kool).

I generally do not bother to open them up each year (and we have 4).
Generally, not that much dirt and dust collects inside.  A cover during
the winter also helps.

Use a vacuum cleaner on the condenser coils in the back and any other easily
accessible dirt traps.

If you do take the cover off, check the fan motor for free rotation.  If
it is tight indicating bad bearings or lack of lubrication, it will have
to be disassembled, cleaned, and lubricated - or replaced.  If there are
lubrication holes at the ends of the motor, put a couple drops of electric
motor oil in there while you have it open.

These units have a sealed freon system - so if anyone's been into it
before - you can tell from obvious saddle valves clamped on.  Generally,
if it cools and the air flow is strong, it is OK.

These units tend to be very reliable and low maintenance.

  15.17) Window air conditioner doesn't cool

This means the fan runs but you do not hear the compressor kick in.

It could be several things:

* If you hear the 'click' of the thermostat but nothing happens (Your room
  lights do not dim even for a second) and there is no other sound, it could
  be bad connections, bad thermostat, dirty switch contacts, bad compressor,
  etc.  Or, you have it set on fan instead of cool.  Try cycling the mode
  selector switch a couple times.

* If you do not hear a click at all, then the thermostat is probably bad or
  it is cooler in your room than you think!  Try tapping on the thermostat.
  Sometimes they just stick a bit after long non-use.

* If you get the click and the lights dim and then a few seconds later there
  is another click and the lights go back to normal, the compressor, or its
  starting circuitry is bad.  It is trying to start but not able to get up to
  speed or rotate at all.

Except for a bad compressor, all these are repairable relatively inexpensively
but if it is real old, a new high efficiency model may be a better solution.

  15.18) Air conditioner freezes up

When this happens, airflow is reduced greatly since ice is blocking the
evaporator.  Turning the unit off for a while or running it on fan-only
will clear the ice but this may indicate the need for maintenance or an
actual problem.  Similar comments apply to window and central air conditioners
as well as heat pumps.

The three major causes of an air conditioner freezing up are:

1. Reduced airflow due to a dirty filter or clogged evaporator.  If you are
   not aware that there is a filter to clean, this is probably the cause :-).

2. Low Freon.  While your intuition may say that low Freon should result in
   less cooling, what happens is that what is there evaporates too quickly
   and at the input end of the evaporator coils resulting in lower temperatures
   than normal at that end (which results in condensed water vapor freezing
   instead of dripping off) but part of the evaporator will likely be too warm.

   You cannot fix this yourself without specialized equipment.  For a room
   air conditioner that isn't too old, it may be worth taking it in to a
   reputable shop for an evaluation.  For a central air conditioner, you will
   have to call an HVAC service company for repairs.

   The fact that the Freon is low means that there is a leak which would also
   need to be repaired.  Freon does not get used up.

3. Outside and/or inside temperature may be very low.  The unit may not be
   designed to operate below about 65 degrees F without freezing up.

If it is 90 degrees F and you have full air flow with the fan set on high and
still get the freezup on a part of the evaporator, then low Freon is likely.

  15.19) Comments on electric clothes dryer problems and repair

For quite a lot of useful information, do a web search for 'appliance 
repair'.  There are a couple of decent sites with DYI information.

(From: Bernie Morey (bmorey@aardvark.apana.org.au)).

I've repaired our electric dryer several times over the years and kept it 
going well beyond its use-by date.

My main problems have been:

1. Mechanical timer failure.  Easy fix.

2. Leaking steam damaging the element.  Have replaced element twice -- fairly
   easy job.  Had to replace some stainless stand-offs at the same time.  
   Elements readily available and equivalent of USD24 each.

3. Bearing replacement -- have to be done carefully or they don't last.

4. Belt replacement.  (Make sure you center the belt with respect to the idler
   and rotate the drum by hand to double check it before buttoning things up.
   Else, it may pop off the first time the motor starts.  --- sam).

5. Exhaust fan bearing replacement.  This was the trickiest, although far 
   from impossible.  It is a sealed unit subject to high heat and dust 
   contamination -- not a good environment.

The only problem for the past two years has been the dryer throwing the 
exhaust fan belt.  Cleaning up the fluff fixes it for another year.

Did all these without any guide -- just carefully inspecting the work before 
starting and making diagrams of wiring and ESPECIALLY the main drum belt.  I 
generally have to get my wife to help me with the main belt -- hard to get 
the tensioner in position while stopping the belt slipping down the far side 
of the drum.

These things are mechanically and electrically pretty simple -- if it's not 
working the fault is usually obvious.

  15.20) Dryer shuts down after a few minutes

There are multiple thermostats in a dryer - one that sets the air temperature
during normal operation (and controls power to the heating element) and one or
more that sense fault conditions (and may shut everything down) such as those
described below.

(From: Bernie Morey (bmorey@aardvark.apana.org.au)).

The dryer is likely cutting out because a thermostat is tripping.  The
fundamental reason is probably that the exhaust air is too  hot.  And the air
flow is probably too hot because it is restricted -- lower  volume of air at
higher temperature.  Check these things out:

1. Lint filter.  Although these can look clean (and I assume you do clean 
   it after every load!) the foam variety can gradually clog up with very fine 
   dust and restrict air flow.  If it's a foam disk, a new one is fairly cheap.

2. Can you feel the exhaust air?  If not, the exhaust fan belt may be worn 
   broken or slipping.  The exhaust fan bearing could be partly seized -- try 
   turning the fan by hand and check for stiffness.

3. Air outlet blockage.  Lint and dust may have built up in the exhaust 
   side of the machine.  Check for restrictions.  Our machine just vents up 
   against the laundry wall as it is too difficult to vent it to the outside. 

   Outside vents are often plastic tubing with a spiral spring steel coil for 
   stiffness -- check for kinks or obstructions.

4. 'Clutching at straws' Dept #1:  Element may have developed a hot-spot 
   near a thermostat.  Involves dismantling the machine and checking the 
   element.  NB -- if you dismantle the machine, make a diagram of how the 
   drive belt fits over the drum, motor, and idler!

5. 'Clutching at straws' Dept #2:  The drum may be restricted from turning 
   freely.  This would slow the motor and hence the exhaust fan.  Check for 
   socks, women's knee-highs (these thing seem to breed everywhere!) & caught 
   near the bearings (probably the front).

You cannot completely check the thermostat with a meter -- they are either
open or closed.  To test it properly you would have to know the temperature 
at which it opens (from the manufacturer's specs), and then measure the 
temperature of the exhaust air with a probe while watching the thermostat. 

  15.21) Why has my dryer (or other high current) plug/socket burned up?

This sort of failure is not unusual.  The brass (or whatever) corrodes a
bit over time and/or the prongs loosen up.  It doesn't take much resistance
at 20 or 30 Amps to produce a substantial amount of heat.  The hotter it gets,
the more the resistance goes up, heating increases, it loosens more, and so
on until something melts.  The power is I*I*R (where I is current and R
is the resistance) so at 20 A, a .1 ohm resistance at the contact results
in 40 W - think of the heat of a 40 W light bulb.

An exact cause would be hard to identify.  However, only the plug and
receptacle are involved - this is not a case of an outside cause.  Such
a failure will not normally blow a fuse or trip a breaker since the current
does not increase - it is not a short circuit.

It is definitely wise to replace both the plug and receptacle in such
cases since at the very least, the socket has lost its springiness due to
the heating and will not grip well..  Make sure that the prongs on the new
plug make a secure fit with the socket.

On plugs having prongs with a pair of metal strips, spreading them out a bit
will make much better contact in an old receptacle.

In general, if a plug is noticeably warm, corrective action should be taken
as it will likely get worse.  Cleaning the prongs (with 600 grit sandpaper)
and spreading the metal strips apart (if possible) should be done first but
if this does not help much, the plug and/or socket should be replaced.
Sometimes, the original heating problem starts at the wire connections to
the plug or socket (even inside molded units) - loose screws, corroded wires,
or deteriorated solder joints.

  15.22) Four year old gas dryer just started popping GFCI

Why is it on a GFCI in the first place?  A grounded outlet is all the
protection that is needed and any type of appliance with a motor or transformer
could be a potential nuisance tripper with a GFCI (though not always).

As to why it is now different, I assume that this is a dedicated outlet so
nothing else you added could affect it.  Thus you are left with something
changing in the dryer or the GFCI somehow becoming overly sensitive.

It is possible that there is now some electrical leakage in the dryer wiring
just from accumulated dirt and grime or dampness.  This could be measured
with an AC milliamp meter or by measuring the resistance between the AC wires
and the cabinet.  If this test shows up nothing, I would recommend just
putting on a grounded outlet without a GFCI.  It could also be that due
to wear, the motor is working harder at starting resulting in just a tad
more of an inductive current spike at startup.

  15.23) Checking dishwasher solenoids

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

Greetings. Well, since it's a moist/damp environment... I'd suspect a
bad connection first. You will need to pop off the front bottom panel
and get at the wires that actually connect the solenoid to the timer
motor (and/or wire harness). You will need an ohmmeter to check the
resistance of the coil - if it's OK (20-200 ohms I would guess), that's
not the problem. Well, that leaves you with pretty much the wires that
connect the timer motor (a MULTI-contact switch driven by a timer motor
like those found in old clocks that plugged into outlets) and the switch
itself. I hope the dishwasher is unplugged... Since the dishwasher
operates as a closed system (because of the "darned" water :-) it will
be difficult to test it in circuit. I suggest that you try to trace
the wires that come off the solenoid to their other ends... and then test
the wires themselves. If you feel this is too much for you, call the
repair folks - ask around... see if anyone else knows a particular
service that has a good record...

Chapter 16) Electrical Wiring Information and Problems

  16.1) Safe electrical wiring

This chapter is in no way intended to be a comprehensive coverage of wiring
issues but includes a discussion of a few of the common residential wiring
related questions.  For more information, see the official Usenet Electrical
Wiring FAQ or a DIY book on electrical wiring.  The NEC (National Electrical
Code) handbook which is updated periodically is the 'bible' for safe wiring
practices which will keep honest building inspectors happy.  However, the NEC
manual is not what you would call easy to read.  A much more user friendly
presentation can be found at the CodeCheck web site:

* http://www.codecheck.com/

This site includes everything you always wanted to know about construction
codes (building, plumbing, mechanical, electrical) but were afraid to ask.

In particular, the following series of sections on Ground Fault Circuit
interrupters is present at the CodeCheck web site and includes some nice
graphics as well.

  16.2) What is a GFCI?

A Ground Fault Circuit Interrupter (GFCI) is a device to protect against
electric shock should someone come in contact with a live (Hot) wire and
a path to ground which would result in a current through his/her body.  The
GFCI operates by sensing the difference between the currents in the Hot and
Neutral conductors.  Under normal conditions, these should be equal.  However,
if someone touches the Hot and a Ground such as a plumbing fixture or
they are standing in water, these currents will not be equal as the path is
to Ground - a ground fault - and not to the Neutral.  This might occur
if a short circuit developed inside an ungrounded appliance or if someone
was working on a live circuit and accidentally touched a live wire.

The GFCI will trip in a fraction of a second at currents (a few mA) well
below those that are considered dangerous.  Note that a GFCI is NOT a
substitute for a fuse or circuit breaker as these devices are still
required to protect equipment and property from overloads or short
circuits that can result in fire or other damage.

GFCIs can be installed in place of ordinary outlets in which case they
protect that outlet as well as any downstream from it.  There are also
GFCIs that install in the main service panel.

Note that it may be safe and legal to install a GFCI rated at 15 A on a
20 A circuit since it will have a 20 A feed-through.  Of course, the GFCI
outlet itself can then only be used for appliances rated 15 A or less.

Many (if not most) GFCIs also test for a grounded neutral condition where a
low resistance path exists downstream between the N and G conductors.  If such
a situation exists, the GFCI will trip immediately when power is applied even
with nothing connected to the protected outlets.

  16.3) GFCIs, overloads, and fire safety

A GFCI is NOT a substitute for a fuse or circuit breaker (unless it is a
combined unit - available to replace circuit breakers at the service panel).

Therefore, advice like "use a GFCI in place of the normal outlet to prevent
appliance fires" is not really valid.

There may be some benefit if a fault developed between Hot and Ground but that
should blow a fuse or trip a circuit breaker if the outlet is properly wired.
If the outlet is ungrounded, nothing would happen until someone touched the
metal cabinet and an earth ground simultaneously in which case the GFCI would
trip and provide its safety function.  See the section: "Why a GFCI should not
be used with major appliances" for reasons why this is not generally
desirable as long as the appliance or outlet is properly grounded.

However, if a fault occurs between Hot and Neutral - a short in the motor, for
example - a GFCI will be perfectly happy passing almost any sort of overload
current until the GFCI, wiring, and appliance melts down or burns up - a GFCI
is not designed to be a fuse or circuit breaker!  That function must be
provided separately.

  16.4) How does a GFCI work

GFCIs typically test for the following condition:

1. A Hot to Ground (safety/earth) fault.  Current flows from the Hot wire to
   Ground bypassing the Neutral.  This is the test that is most critical for

2. A grounded neutral fault.  Due to miswiring or a short circuit, the N and G
   wires are connected by a low resistance path downstream of the GFCI.  In
   this case, the GFCI will trip as soon as power is applied even if nothing
   is connected to its protected (load) circuit.

To detect a Hot to Ground fault, both current carrying wires pass through the
core of a sense coil (transformer).  When the currents are equal and opposite,
there is no output from its multiturn sense voltage winding.  When an imbalance
occurs, an output signal is produced.  When this exceeds a threshold, a circuit
breaker inside the GFCI is tripped.

GFCIs for 220 VAC applications need to monitor both Hots as well as the
Neutral.  The principles are basically the same: the sum of the currents in
Hot1 + Hot2 + Neutral should be zero unless a fault exists.

To detect a grounded neutral fault, a separate drive coil is continuously
energized and injects a small 120 Hz signal into the current carrying
conductors.  If a low resistance path exists between N and G downstream
of the GFCI, this completes a loop (in conjunction with the normal connection
between N and G at the service panel) and enough current flows to again
trip the GFCI's internal circuit breaker.

GFCIs use toroidal coils (actually transformers to be more accurate) where the
core is shaped like a ring (i.e., toroid or doughnut).  These are convenient
and efficient for certain applications.  For all practical purposes, they are
just another kind of transformer.  If you look inside a GFCI, you will find a
pair of toroidal transformers (one for H-N faults and the other for N-G faults
as described above).  They look like 1/2" diameter rings with the main current
carrying conductors passing once through the center and many fine turns of
wire (the sense or drive winding) wound around the toroid.

All in all, quite clever technology.  The active component in the Leviton
GFCI is a single chip - probably a National Semiconductor LM1851 Ground Fault
Interrupter.  For more info, check out the specs at National'a web site at:

  16.5) More on how the GFCI detects a N-G short

To detect a Neutral to Ground fault there is a second transformer placed
upstream of the H-G sense transformer (see the illustration of the internal
circuitry of the GFCI at: http://www.national.com/pf/LM/LM1851.html).  A small
drive signal is continuously injected via the 200 T winding which induces
equal voltages on the H and N wires passing through its core.

* If N and G are separate downstream (as they should be), no current will be
  flow in either wire and the GFCI will not trip.  (No current will flow in
  the H wire as a result of this stimulus because the voltage induced on both
  H and N is equal and cancels.)

* If there is a N-G short downstream, a current will flow through the N wire,
  to the G wire via the short, and back to the N wire via the normal N-G
  connection at the service panel.  Since there will be NO similar current in
  the H wire, this represents a current unbalance and will trip the GFCI in
  the same manner as the usual H-G short.

* Interestingly, this scheme automatically detects a H-H fault as well.  This
  unlikely situation could occur if the Hots from two separate branch circuits
  were accidentally tied together in a junction box downstream of the GFCI.
  It works the same way except that the unbalance in current that trips the
  GFCI flows through the H wire, through the H-H fault, and back around via
  the Hot busbar at the service panel.  Of course if the two Hots are not on
  the same phase, there may be fireworks as well :-).

  16.6) GFCIs and safety ground

Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be
installed in a 2 wire circuit, the GFCI does not create a safety ground.
In fact, shorting between the Hot and Ground holes in the GFCI outlet
will do absolutely nothing if the GFCI is not connected to a grounded
circuit (at least for the typical GFCI made by Leviton sold at hardware
stores and home centers). It will trip only if a fault occurs such that
current flows to a true ground.  If the original circuit did not have a
safety ground, the third hole is not connected.  What this means is that
an appliance with a 3 prong plug can develop a short between Hot and the
(supposedly) grounded case but the GFCI will not trip until someone
touches the case and an earth ground (e.g., water pipe, ground from
some other circuit, etc.) at the same time.

Note that even though this is acceptable by the NEC, I do not consider it
desirable.  Your safety now depends on the proper functioning of the GFCI
which is considerable more complex and failure prone than a simple fuse or
circuit breaker.  Therefore, if at all possible, provide a proper Code
compliant ground connection to all outlets feeding appliances with 3 wire

  16.7) Where are 3 wire grounded outlets required?

If you move into a house or apartment where some or all of the outlets are the
old 2 prong ungrounded type, don't panic.  There is no reason to call an
electrician at 2:00 AM in the morning to upgrade them all at great expense.

You don't need grounded outlets for two wire appliances, lamps, etc.  They
do essentially nothing if the third hole isn't occupied :-).  A GFCI will
provide much more protection!

You should have grounded outlets for the following:

* Computers in order for the line filters and surge suppressors to be most

* High-end entertainment gear if it uses 3 prong plugs for similar reasons.

* Microwave ovens.  For safety, these really should be on a grounded circuit.
  (A GFCI will not protect against a fault on the high voltage side of a
  microwave oven, though this sort of fault is extremely unlikely).

* Large appliances including refrigerators, clothes washers and dryers,
  dehumidifiers, window air conditioners, etc.

In most cases, there will only be a few circuits where this is needed and only
these need to be upgraded.  To what extent the wiring plan of your residence
separates lighting type circuits from those with outlets that will be used for
3 wire equipment will determine how easy it is to upgrade only those outlets
that are affected.  It may be cheaper to just add new branch circuits for
specific equipment needs.

  16.8) Why you should NOT connect H to N

The question often arises: "Why can't I just connect the H to the N if my
outlets are only two prong?"

For one reason, consider the 'appliance' below:

             |                 |        Open Fault
  Hot o---------o-o----/\/\---------+------ X -----o Neutral
             | Switch  Load    |    |
             |  (On)           |----+ Case should be G but is connected to N

With the appliance 'on', current passes through the internal wiring/motor/etc.
of the appliance to the N but this is now connected to the case as well.  If
the house wiring opens (or even if the plug is loose, it is possible to have
line voltage on the case.

  16.9) Testing installed GFCIs

The built-in tester is designed to actually introduce a small leakage
current so its results should be valid.  Therefore, testing a single
GFCI outlet with an external widget is not really necessary except for
peace-of-mind.  However, such a device does come in handy for identifying
and testing outlets on the same circuit that may be downstream of the GFCI.

An external tester is easy to construct - a 15 K ohm resistor between H and G
will provide a 7 mA current.  Wire it into a 3 prong plug and label it "GFCI
Tester - 7 mA".  The GFCI should trip as soon as you plug the tester into a
protected outlet.  On a GFCI equipped for grounded neutral detection (as most
are), shorting the N and G conductors together downstream of the GFCI should
also cause it to trip.

Note that such a tester will only work for GFCI protected outlets that are on
grounded (3 wire) circuits (unless you add an external ground connection).
Thus, just using a commercial tester may falsely indicate that the GFCI is bad
when in fact it is simply on an ungrounded outlet (which is allowed by Code in
a retrofit situation).

The test button will work whether or not the circuit includes a safety ground
because it passes an additional current through the sense coil between Hot and
Neutral tapped off the wiring at the line side of the GFCI and therefore
doesn't depend on having a safety Ground.

I suppose you can purchase suitable low cost testers as well (but they are
subject to the same must-be-grounded restrictions).  Try your local home
center or electrical supply distributor.

  16.10) John's comments on the use of GFI breakers

(From: John Grau (affordspam@execpc.com)).

I personally would not feed a subpanel with a GFI breaker.  Here are just a
few of the reasons:

1. GFI breakers for personnel protection are set to trip at 5 mA (1/1000ths of
   an Amp). The longer the circuit conductors, the greater the potential for
   leakage. If you subfeed a panel, you would have the cumulative distances of
   all circuits connected to that panel to contend with and hope that the
   breaker would hold.

2. You would not be able to connect any thing to that subpanel that would be a
   critical load. e.g. freezer, sump pump, well pump, furnace, etc. An
   unnoticed nuisance trip, could mean that you would come home to a thawed
   freezer, frozen pipes, flooded basement, etc.

3. Using breakers to achieve GFI protection has 2 downsides: expense, and
   usually, an inconvenient location to reset the tripped device. A GFI outlet
   at the point of usage, is usually more convenient to reset, should it trip.
   Here in Wisconsin, I can buy about 6 GFI outlets for the cost of 1 breaker. 

There is no compulsory language in the National Electrical Code the forces an
update to current code standards, unless you repair, replace or update the
affected component. Not all changes in the 1996 code made sense, and I would
not update the wiring in my own home (built in 1995) to current standards.

  16.11) Phantom voltage measurements of electrical wiring

When making measurements on household wiring, one expects to see one of three
voltages: 0, 115 VAC, or 230 VAC (or very similar).  However, using a typical
multimeter (VOM or DMM) may result in readings that don't make sense.  For
example, 2 VAC between Neutral and safety Ground or 40 VAC between a Hot wire
(with its breaker off) and Neutral or safety Ground.

The most likely reason for these strange readings is that there is E/M
(electromagnetic) coupling - capacitive and/or inductive - between wires which
run near one another - as inside a Romex(tm) cable.  Where one end of a wire
is not connected to anything - floating, the wire acts as an antenna and picks
up a signal from any adjacent wires which are energized with their 60 (or 50)
Hz AC field.  There is very little power in these phantom signals but due to
the very high input resistance/impedance of your VOM or DMM, it is picked up
as a voltage which may approach the line voltage in some cases.

Another possibility is that the you didn't actually walk all the way down to
the basement to shut off power completely and the circuit is connected to a
high tech switch (such as one with a timer or an automatic dimming or off
feature) or a switch with a neon light built in.  There will be some leakage
through such a switch even if it is supposed to be off - kill power completely
and test again.

Putting any sort of load between the wires in question will eliminate the
voltage if the cause is E/M coupling.  A small light bulb with test probes can
be used to confirm this both by serving as a visual indication of significant
voltage (enough to light the bulb, if weakly) and to short out the phantom
voltage for testing with the multimeter.

There can be other causes of such unexpected voltage readings including
incorrect or defective wiring, short circuits in the wiring or an appliance,
and voltage drops due to high current in a circuit.  However, the E/M coupling
explanation is often overlooked when using a multimeter.

  16.12) Determining wiring of a 2-wire outlet

Connect a wire between one prong of a neon outlet tester and a known ground -
cold water pipe if copper throughout, heating system radiator, ground rod, etc.

(Experienced electricians would just hold onto the other prong of the tester
rather than actually grounding it.  Their body capacitance would provide
enough of a return path for the Hot to cause the neon to glow dimly but
you didn't hear this from me :-).  Yes, they survive without damage and don't
even feel anything because the current is a small fraction of a mA.  DON'T
try this unless you are absolutely sure you know what you are doing!)

With one prong grounded, try the other prong in the suspect outlet:

* The Hot should glow brightly and the Neutral should not light at all.  This
  is the normal situation.

* If neither side glows, the fuse is blown, the circuit breaker is tripped,
  this is a switched outlet and the switch is off, or there is a wiring
  problem elsewhere - or your ground isn't really ground.

* If both sides glow and using the tester between the slots results in no glow,
  then you have an open Neutral and something else on the circuit that is on is
  allowing enough current to flow to light the neon tester.

* If both sides glow and using the tester between the slots results in an even
  brighter glow, the outlet is wired for 220 V, a dangerous violation of the
  NEC Code unless it is actually a 220 V approved outlet.  It is unlikely you
  will ever see this but who knows what bozos worked on your wiring in the

  16.13) Outlet wiring screwed up?

So your $6 outlet tester displays a combination of lights that doesn't
make sense or one or more lights is dim.  For example, all three lights
are on but K and X (see below) are dim.

The three neon bulbs are just between what should be (The first letter is
how the light is marked on mine):

K Hot to Ground (GROUND OK).
O Hot to Neutral (HOT OK?).
X Neutral to Ground (HOT/NEUTRAL REVERSE - should not light).

I suspect at the very least that your ground is not connected at the
service panel.  I may run from some/all the outlets but ends somewhere.
You are seeing capacitive/inductive pickup between the floating ground
and the other wires in the circuit.  Your N and H may be reversed as well
but this cannot be determined without checking with a load between H/N
and a proper ground.

I would recommend:

1. Determining if the ground wire for those 3 prong outlets does indeed
   go anywhere.

2. Determining if the Hot and Neutral polarity is correct by testing between
   each of the prongs and a confirmed ground (properly connected 3 prong
   outlet, service panel, or a cold water pipe in an all metal water system)
   with a load like a 25 W light bulb.  The neon lamps in the tester or a high
   impedance multimeter can be fooled by capacitance and other leakage paths.

For a computer or other 3 wire appliance, you should really install a
proper 3 prong outlet wired correctly.  Otherwise, any power line filters
and surge suppressors will not have the safety ground (which a GFCI does
NOT create).  Some UPSs may get away without one but then their surge
suppressor and/or line filters will not work correctly.

Some appliances like microwave ovens MUST have a proper safety ground
connection for safety.  This not only protects you from power line
shorts to the case but also a fault which could make the case live
from the high voltage of the microwave generator.

  16.14) 220 V outlet reads 0 VAC between slots

"I have a 220 outlet that I need to plug an AC unit into.  The AC unit works
 fine in another outlet, but not in this specific outlet.  I pulled out my
 handy dandy meter and checked the voltage across the two line slots - the
 meter read 0.

 But when I tried one line and the ground I got 125 V.  Similarly, when I
 tried the other line and the ground I also got 125 V.  What's the scoop?  Why
 does the meter, and obviously the AC, think that there isn't 220 V coming in?
 Any help is greatly appreciated - as this room is stinking hot right now!"

Did it ever work?  It sounds like both slots are being fed from the same
phase of the power from the service panel.  Check with a load like a 100
W light bulb between each slot and ground.  This could have happened during
the original installation or during renovation.

Another possibility is that there is some other 220 V appliance on the
same line with its power switch in the ON position (and not working either)
AND one side of the line has a tripped breaker or blown fuse.

Yet another possibility:

(From: David L. Kosenko (davek@informix.com)).

My load center is GE unit.  They make both full height and half height breakers.
If you use a half height breaker set for a 220 line, you must be careful to
install it across the two phases.  It is very easy (especially if you don't
know about 220) to place the ganged breakers into a single full height slot in
the load center, giving you both lines off the same phase line.

  16.15) Testing for fault in branch circuit

This may trip the breaker or blow a fuse - or trip a GFCI if so protected.
The procedure below is specifically for GFCI tripping.  You will need a

* First, unplug everything from the circuit and see if it still trips.  If
  it now does not trip, one of the appliances was the problem.  Try them one
  at a time to see which is the problem and then check the section for that
  or a similar appliance elsewhere in this document.

Assuming the circuit is at fault:

* You need to determine whether this is a H-G leakage fault (which is what
  most people think is the only thing GFCIs test for) or a shorted G-N fault.

* A H-G fault that doesn't trip the normal breaker might be due to damp
  wiring (an outside outlet box that gets wet or similar) or rodent damage.

* A shorted G-N fault means that G and N are connected somewhere downstream
  of the GFCI - probably due to incorrect wiring practices or an actual
  short circuit due to frayed wiring or wires touching -  damage during
  installation or renovation.

Assuming the line is separate from any other wiring:

* With the line disconnected from the service panel (all three wires), first
  test between each pair of wires with the multimeter on AC to make sure it is
  truly dead - there should be virtually no voltage.  H-G, N-G, and H-N should
  all be close to 0 (say, less than a volt).

* If this passes, test across the dead line's H and G for leakage on the
  resistance range.  It should be greater than 15 K ohms (it should really
  be infinity but to trip the GFCI requires around 15 K ohms or less).

* Then, test for resistance between H and G - this too should be infinity.

One of these will show a fault - possibly the N-G test indicating a short or
improperly wired outlet since this would not result in any operational
problems until a GFCI is installed (though it does represent a safety

  16.16) Locating wires inside a wall

There are gadgets you can buy that look like test lights but sense the
electric field emitted by the Hot wire.  It is also possible to inject
a signal into the wire and trace it with a sensitive receiver.

However, if you are desperate, here is a quick and easy way that is worth
trying (assuming your wiring is unshielded Romex - not BX - and you can power
the wire).  Everything you need is likely already at your disposal.

Get a cheap light dimmer or a fixture with a light dimmer (like that halogen
torchier that is now in the attic due to fire safety concerns) and plug it
into an outlet on the circuit you want to trace.  Set it about half brightness.

Now, tune a portable AM radio in between stations.  If you position the
radio near the wire, you should hear a 120 Hz hum - RFI (Radio Frequency
Interference) which is the result of the harmonics of the phase controlled
waveform (see the section: "Dimmer switches and light dimmers".  Ironically,
the cheaper the dimmer, the more likely this will work well since no RFI
filtering is built in.

I have tried this a bit and it does work though it is somewhat quirky.  I do
not know how sensitive it is or over how large a circuit it is effective.
It is somewhat quirky and even normal power may have enough junk on the 
waveform to hear it in the radio.  However, with a partner to flip the dimmer
off and on to correlate its position with what you hear, this may be good

  16.17) Bad Neutral connections and flickering lights or worse

Residential service comes from a centertapped 110-0-110 V transformer on the
utility pole.  There are 3 wires into your house - 2 Hot or live wires and the
Neutral which is the centertap of the transformer.  If the connection between
the Neutral bus in your service panel and the pole transformer centertap
becomes loose and opens or develops a high resistance, then the actual voltage
on either of the Hots with respect to the Neutral bus (which is divided among
your branch circuits) will depend on the relative loads on either side much in
the way of a voltage divider using resistors.  Needless to say, this is an
undesirable situation.

Symptoms include excessive flickering of lights (particularly if they get
brighter) when large appliances kick in, light bulbs that seem too bright
or too dim or burn out frequently, problems with refrigerators or freezer
starting due to low voltage, etc.  In the worst case, one set of branch
circuits can end up with a voltage close to 220 VAC - on your poor 110 V
outlets resulting in the destruction of all sorts of appliances and
electronics.  The opposite side will see a much reduced voltage which may be
just as bad for some devices.

It is a simple matter for an electrician to tighten up the connections but
this is not for the DIY'er unless you are familiar with electrical wiring and
understand the implications of doing anything inside the service panel while
it is live!

  16.18) Lightning storm trips GFCIs protecting remote outdoor outlets

"I have several outdoor 110V outlets, protected by GFCI breakers. These
 circuits nearly always trip when there are nearby lightening strikes.
 I am satisfied that there is no short circuit caused by water as :

 * A lightning storm without rain will still trip the GFCI.

 * Water from the sprinklers does not cause a problem.

 * I can immediately reset the GFCI when it is still raining and it comes
   back on.

 The electrical cables buried underground run for about 600 feet.

 Is GFCI tripping caused by electrical storms normal ? Are my GFCI breakers too
 sensitive ? Is there any way to modify the circuits to avoid this?"

This doesn't surprise me.  Long runs of cable will be sensitive to the
EM fields created by nearby lightning strikes.  Those cables probably
have 3 parallel wires: H, N, G.  The lightning will induce currents in 
all three which would normally not be a problem as long as H and N are
equal.  However, I can see this not being the case since there will be
switches in the Hot but not the Neutral so currents could easily unbalance.

These are not power surges as such and surge suppressors will probably not

Since it happens with all of your GFCIs, it is not a case of a defective unit.
Perhaps there are less sensitive types but then this would reduce the
protection they are designed to provide.

  16.19) GFCI trips when it rains (hard)

Most likely, moisture/water is getting into some portion of the GFCI's
protected wiring (at the GFCI or anywhere downstream) and the GFCI is
simply doing its job.  You will have to trace the wiring through all
junction boxes and outlets to determine where the problem is located.
Yes, I know this may not be your idea of fun!

  16.20) Why a GFCI should not be used with major appliances

A Ground Fault Circuit Interrupter is supposed to be a valuable safety
device.  Why not use them everywhere, even on large appliances with
3 wire plugs?

1. A properly grounded 3 prong outlet provides protection for both people
   and the appliance should a short circuit develop between a live wire
   and the cabinet.

2. Highly inductive loads like large motors or even fluorescent lamps or
   fixtures on the same circuit can cause nuisance tripping of GFCIs which
   needless to say is not desirable for something like a refrigerator.

  16.21) Toasters and GFCIs

The following is a reason to use GFCIs on kitchen outlets that may not
be obvious:

(From: David Buxton (David.Buxton@tek.com)).

In addition to the usual explanations dealing with safety around water,
another reason why kitchen outlets need a GFCI is the toaster.  All too 
often people stick a butter knife in there to dislodge some bread.  If 
the case was grounded there would be short from the element to the case. 
So toasters are two wire instead of 3-pronged.  So, you must have a GFCI 
for any outlet that might take on a toaster.

  16.22) Reverse polarity outlets - safety and other issues

"Our new home has reverse polarity in all of the electrical outlets.  The
 house inspector didn't seem to think this was a major problem, and neither
 did he think it was worth fixing.  Can anyone explain how this might matter
 for us?  The best I understand this is that when something is plugged in, even
 when it's not turned on, there is  still a current going through it--is that
 true at all, or is that normal?  Our biggest concern is our computers, and the
 possibility that our surge protectors won't be effective.  If anyone could
 clear this up, that would be great."

New as in brand new or new for you?  If it is a totally new home, the builder
should have them fixed and you should not sign off on the house until this is
done.  While there is no imminent danger, the house inspector was being a bit
too casual for my tastes.  It is not a big deal as in should stop you from
going through with the purchase but it really should be fixed.

As far as current present when the appliance is off, this is not quite true.
When properly wired, the power switch is the first thing in the circuit so it
cuts off power to all other parts of the internal wiring.  With the reversal,
it is in the return - the rest of the wiring will be live at all times.  Except 
or servicing, this is really not that big a concern and does not represent any
additional electricity usage.

Normally (I assume these are 3 prong grounded outlets) you have the following:

* Hot - the live conductor - the narrow slot.
* Neutral - the return for the current used by the device - the wide slot.
* Ground (or safety ground) - the U shaped slot.

Reverse polarity means that Hot and Neutral are interchanged. (any other
variation like an interchange with the ground represents a serious safety
hazard and it should be corrected as soon as possible.  The outlet should
not used until it is).

For most appliances and electronics, this does not really matter.  By
design, it must not represent a safety hazard.  However, there can be
issues - as you are concerned - with surge suppressors and susceptibility
to interference.  In some cases, the metal case of a stereo could be
coupled to the Neutral by a small capacitor to bypass radio frequency
interference.  This will be coupled now to Hot instead.  While not a
safety hazard, you might feel an almost imperceptible tingle touching
such a case.

Surge suppressors may or may not be affected (to the extent that they are
ever effective in any case - unplugging the equipment including modem lines
and the like during an electrical storm is really the only sure protection
but that is another section).  It depends on their design.  Some handle the
3 wires in an identical manner and interchanging them makes no difference.
Others deal differently with the Hot and Neutral in which case you may lose
any protection you would otherwise have.

My advice: If you are handy electrically, correct them yourself.  If not,
get them corrected the next time you have an electrician in for any reason.
It is a 5 minute job per outlet unless the wiring is extremely screwed up.

Use a properly wired outlet for your computer to be doubly sure.

It is not an emergency but I consider proper wiring to be very desirable.

Here is another example:

"I was checking some outlets in my apartment. As I recall, the narrow prong
 should be hot, i.e., there should be 120 V between it and the wide prong or
 the ground prong. The wide prong should be neutral, i.e., it should show no
 voltage relative to the ground prong. Well, it appears that the Neutral
 and Hot wires are reversed in some outlets. In others, they are correct."

Well, there should be very little voltage although it may not be 0.

Reversed polarity outlets are not unusual even in new construction.

Reversed H and N is not usually dangerous as appliances must be designed
so that no user accessible parts are connected to either H or N - even
those with polarized plugs.  Think of all the times people use such appliances
in old unpolarized outlets or with unpolarized extensions cords.  (There are
exceptions like electric ranges where there may be no separate safety ground
conductor but I assume you are talking about branch circuits, not permanently
wired-in appliances.)

"In still others, I get some voltage between ground and either the wide or
 narrow prong. Ack. Should I worry? Should I do more than worry?"

You should, of course, measure full line voltage between the H and G.  The
safety ground, G, does not normally carry any current but is at the same or
nearly the same potential as N.

The voltage between G and (actual) N if quite low - a couple volts or less - is
probably just due to the the voltage drop in the current carrying N wire.  Turn
off everything on this branch circuit and it should go away.  However, there
could also be a bad (high resistance connection) somewhere in the N circuit.

If the voltage reads high to either H or N - say, 50 volts - and you are
measuring with a high impedance multimeter, this is probably just due to an
open ground: a three prong outlet was installed without connecting the ground
(in violation of Code unless on a GFCI) and this leakage is just due to
inductive/capacitive pickup from other wires.

Full line voltage on the G conductor relative to an earth ground (like a
copper cold water pipe) would represent a serious shock hazard to be corrected
as soon as possible - the appliance or outlet should *not* be used until
the repair is made.  While unlikely, for anyone to screw up this badly, it
could happen if someone connected the green or copper wire, or green screw
to H instead of G.

In any case, it would be a good idea to correct the H-N reversals and determine
if the voltage on the G is an actual problem.

  16.23) Comments on whole house surge suppressors

These are typically offered your power company:

"I have a surge suppressor that was put between my meter and the service
 panel.  It's rented from my power company.  The advertised product is part of
 a 'package' that includes plug in surge suppressors.  The package price is
 $4.95/month.  I didn't want the plug in suppressors so they said that it
 would be $2.75/month.  Is this a good deal?"

(From: Kirk Kerekes (redgate@oklahoma.net)).

The power company just passes on the warranty of the manufacturer, which
is, in turn, merely an insurance policy whose premium in included in the
normal retail price of the unit. Basically, the power company is taking a
product with a wholesale cost of about $30, and "renting" it to consumers
for $40-$100 a year. 


Nice work if you can get it.

Note that most homeowner and similar insurance policies _already_ cover
lightning damage, and that the policy from the surge protector is
generally written to only apply to losses not already covered by other
insurance.  As a result, you are paying for insurance that you will likely
*never* be able to make a claim against, even if the device is totally

The simplest whole-house protection is to purchase an Intermatic whole
house surge protector ($40 from Home Depot or Lowe's) and install it
yourself (or pay an electrician to do so -- maybe 15 minutes of work).
Then purchase inexpensive ($10 and under) plug-in surge protectors and
surge-protected power strips and use them all over the house at sensitive
equipment. Note that surge protectors and surge protected power strips
protect the _other_ outlets in the house as well as the ones they contain
(because the MOV's in inexpensive surge protectors are simply connected in
parallel with the power line), so the more of that that you have plugged
in, the more effectively protected your home is. Some power strips need to
be turned "on" for the MOV's to be connected to the power lines.

You can also buy MOV's and add your own custom protection -- but if you
don't already know that, you probably shouldn't be tinkering with such

Note that you should only purchase surge protectors that contain a monitor
LED to tell you if the protector is still functioning -- MOV's deteriorate
when zapped by large surges. This is one reason why I recommend the
multiple-power-strip distributed-protection approach -- it is doubtful
that all of your surge protectors/power strips will get zorched at once.

Chapter 17) All About Wire and the AWG (American Wire Gauge) Numbers

  17.1) Some types of wire

Note: For an understanding of the AWG numbers, you may want to first see the
section: "American Wire Gauge (AWG) table for annealed copper wire".

A semi-infinite variety of wire and cable is used in modern appliances,
electronics, and construction.  Here is a quick summary of the buzz words
so you will have some idea of what your 12 year old is talking about!

* Solid wire: The current carrying conductor is a single solid piece of metal
  (usually copper.  It may be bare, tinned (solder coated), silver plated, or
  something else.

  Solid wire may be used for general hookup inside appliances and electronics,
  and building (and higher power wiring) but not for cords that need to be
  flexible and flexed repeatedly.

* Stranded wire: The current carrying conductor consists of multiple strands
  of copper or tinned copper (though other metals may be found in some cases).
  The individual strands are NOT insulated from one-another.  The wire gauge
  is determined by the total cross sectional area (which may be a bit greater
  than the specified AWG number due to discrete number of strands).  See the
  section: "What about stranded wire?".

  Stranded wire is used for general hookup, building wiring, etc.  It is
  easier to position than solid wire (but tends not to stay put) and more
  robust when flexed repeatedly.  Cordsets always use finely stranded wire
  but despite this, may develop problems due to flexing after long use.

* Magnet wire: This is a solid copper (or sometimes aluminum or silver)
  conductor insulated with a very thin layer of varnish or high-tech plastic.
  This coating must be removed either chemically, by heating in a flame, or
  fine sandpaper, before the wire can be connected to anything.

  Magnet wire is used where a large number of turns of wire must be packed as
  tightly as possible in a limited space - transformers, motors, relays,
  solenoids, etc.

  The very thin insulation is susceptible to nicks and other damage.

* Litz wire: This is similar to stranded wire EXCEPT that the strands are
  individually insulated from each other (like multiple pieces of magnet

  Litz wire is used in high frequency transformers to reduce losses (including
  the skin effect which results in current only traveling near the surface
  of the wire - using multiple insulated strands increases its effective
  surface area).

  Like magnet wire, the insulation needs to be removed from all strands before
  making connections.

* Tinsel wire: A very thin, metallic conductor is wound around a flexible
  cloth or plastic core.

  Tinsel wire is found in telephone and headphone cords since it can be made
  extremely flexible.

  Repair is difficult (but not impossible) since it very fine and the
  conductor must be unraveled from the core for soldering.  The area of the
  repair must be carefully insulated and will be less robust than the rest of
  the cord.

* Shielded wire: An insulated central conductor is surrounded by a metal braid
  and/or foil shield.

  Shielded wire is used for low level audio and video, and other analog or
  digital signals where external interference needs to be minimized.

* Coaxial cable: This is similar to shielded wire but may be more robust and
  have a specified impedance for transmitting signals over long distances.

* Zip cord: This is 2 or 3 (or sometimes more) conductor cable where the
  plastic insulation is scored so that the individual wires can be easily
  separated for attachment to the plug or socket.

* 14/2, 12/3, etc.: These are the abbreviations used for building (electrical)
  wire like Romex (which is one name brand) and for round or zip-type cordset
  wire.  The conductor material is usually copper.

  Note: Some houses during the '50s and '60s were constructed with aluminum
  wiring which has since been found to result in significantly increased risk
  of fire and other problems.  For more information, see the references listed
  in the section: "Safe electrical wiring".  However, aluminum wiring is safe
  if installed according to very specific guidelines (and is used extensively
  in power transmission and distribution - probably for your main connection
  to the utility - due to its light weight and low cost).

  The first number is the AWG wire gauge.

  The second number is the number of insulated conductors (excluding any bare
  safety ground if present).  For example:

  - A 14/2 Romex cable has white and black insulated solid #14 AWG current
    carrying conductors and a bare safety ground (some older similar types of
    cable had no safety ground, however).

  - A 16/3 cordset has white, black and green insulated stranded #16 AWG wires
    (or, overseas, blue, brown, and green or green with yellow stripe).

  17.2) So, where did AWG come from?

Nearly everyone who has done any sort of wiring probably knows that the AWG or
American Wire Gauge number refers to the size of the wire somehow.  But how?

(From: Frank (fwpe@hotcoco.infi.net)).

According to the 'Standard Handbook for Electrical Engineers' (Fink and Beaty)
the 'gauge' you referenced to is 'American Wire Gauge' or AWG and also known
as Brown & Sharp gauge.

According to above handbook, the AWG designation corresponds to the number of
steps by which the wire is drawn. Say the 18 AWG is smaller than 10 AWG and is
therefore drawn more times than the 10 AWG to obtain the smaller cross
sectional area.  The AWG numbers were not chosen arbitrary but follows a
mathematical formulation devised by J. R. Brown in 1857!

  17.3) For the marginally mathematically inclined

Each increase of 3 in the gauge halves the cross sectional area.  Each
reduction by 3 doubles it.  So, 2 AWG 14 wires is like one AWG 11.

It seems that everyone has their own pet formula for this (though I prefer
to just check the chart, below!).

(From: Tom Bruhns (tomb@lsid.hp.com)).

As I understand it, AWG is defined to be a geometric progression with AWG 0000
defined to be 460 mils diameter and 36 gauge defined to be 5.000 mils diameter.
This leads directly to the formula:

              Diameter(mils) = 5 * 92^((36-AWG)/39)

That is, 460 mils is 92 times 5 mils, and the exponent accounts for 39 steps
of AWG number starting at 36 gauge.

(From: David Knaack (dknaack@rdtech.com)).

You can get a fairly accurate wire diameter by using the equation:

          Diameter(inches) = 0.3252 * e^(-0.116 * AWG)

where 'e' is the base of the natural logarithms, 2.728182....

I don't know where it came from, but it is handy (more so if you can do natural
base exponentials in your head).

In its simplest form, the cross sectional area is:

                 A(circular mils) = 2^((50 - AWG) / 3)

  17.4) American Wire Gauge (AWG) table for annealed copper wire

(Similar tables exist for other types of wire, e.g., aluminum.)

(Table provided by: Peter Boniewicz (peterbon@mail.atr.bydgoszcz.pl)).

Wire Table for AWG 0000 to 40, with diam in mils, circular mils,
square microinches, ohms per foot, ft per lb, etc.

   AWG  Dia in  Circ.  Square  Ohm per lbs per Feet/   Feet/    Ohms/
  gauge  mils   Mils   MicroIn 1000 ft 1000 ft Pound    Ohm     Pound
  0000  460.0  211600  166200  0.04901 640.5   1.561   20400   0.00007652
  000   409.6  167800  131800  0.06180 507.9   1.968   16180   0.0001217
  00    364.8  133100  104500  0.07793 402.8   2.482   12830   0.0001935

  0     324.9  105500  82890   0.09827 319.5   3.130   10180   0.0003076
  1     289.3  83690   65730   0.1239  253.3   3.947   8070    0.0004891
  2     257.6  66370   52130   0.1563  200.9   4.977   6400    0.0007778

  3     229.4  52640   41340   0.1970  159.3   6.276   5075    0.001237
  4     204.3  41740   32780   0.2485  126.4   7.914   4025    0.001966
  5     181.9  33100   26000   0.3133  100.2   9.980   3192    0.003127

  6     162.0  26250   20620   0.3951  79.46   12.58   2531    0.004972
  7     144.3  20820   16350   0.4982  63.02   15.87   2007    0.007905
  8     128.5  16510   12970   0.6282  49.98   20.01   1592    0.01257

  9     114.4  13090   10280   0.7921  39.63   25.23   1262    0.01999
  10    101.9  10380   8155    0.9989  31.43   31.82   1001    0.03178
  11    90.74  8234    6467    1.260   24.92   40.12   794     0.05053

  12    80.81  6530    5129    1.588   19.77   50.59   629.6   0.08035
  13    71.96  5178    4067    2.003   15.68   63.80   499.3   0.1278
  14    64.08  4107    3225    2.525   12.43   80.44   396.0   0.2032

  15    57.07  3257    2558    3.184   9.858   101.4   314.0   0.3230
  16    50.82  2583    2028    4.016   7.818   127.9   249.0   0.5136
  17    45.26  2048    1609    5.064   6.200   161.3   197.5   0.8167

  18    40.30  1624    1276    6.385   4.917   203.4   156.6   1.299
  19    35.89  1288    1012    8.051   3.899   256.5   124.2   2.065
  20    31.96  1022    802.3   10.15   3.092   323.4   98.50   3.283

  21    28.46  810.1   636.3   12.80   2.452   407.8   78.11   5.221
  22    25.35  642.4   504.6   16.14   1.945   514.2   61.95   8.301
  23    22.57  509.5   400.2   20.36   1.542   648.4   49.13   13.20

  24    20.10  404.0   317.3   25.67   1.223   817.7   38.96   20.99
  25    17.90  320.4   251.7   32.37   0.9699  1031.0  30.90   33.37
  26    15.94  254.1   199.6   40.81   0.7692  1300    24.50   53.06

  27    14.20  201.5   158.3   51.47   0.6100  1639    19.43   84.37
  28    12.64  159.8   125.5   64.90   0.4837  2067    15.41   134.2
  29    11.26  126.7   99.53   81.83   0.3836  2607    12.22   213.3

  30    10.03  100.5   78.94   103.2   0.3042  3287    9.691   339.2
  31    8.928  79.70   62.60   130.1   0.2413  4145    7.685   539.3
  32    7.950  63.21   49.64   164.1   0.1913  5227    6.095   857.6

  33    7.080  50.13   39.37   206.9   0.1517  6591    4.833   1364
  34    6.305  39.75   31.22   260.9   0.1203  8310    3.833   2168
  35    5.615  31.52   24.76   329.0   0.09542 10480   3.040   3448

  36    5.000  25.00   19.64   414.8   0.07568 13210   2.411   5482
  37    4.453  19.83   15.57   523.1   0.06001 16660   1.912   8717
  38    3.965  15.72   12.35   659.6   0.04759 21010   1.516   13860

  39    3.531  12.47   9.793   831.8   0.03774 26500   1.202   22040
  40    3.145  9.888   7.766   1049.0  0.02993 33410   0.9534  35040
  41    2.808  7.860   6.175   1319    0.02379 42020   0.758   55440

  42    2.500  6.235   4.896   1663    0.01887 53000   0.601   88160
  43    2.226  4.944   3.883   2098    0.01497 66820   0.476   140160
  44    1.982  3.903   3.087   2638    0.01189 84040   0.379   221760

  45    1.766  3.117   2.448   3326    0.00943 106000  0.300   352640
  46    1.572  2.472   1.841   4196    0.00748 133640  0.238   560640

Ohms per 1000 ft, ft per Ohm, Ohms per lb, all taken at 20 degC (68 degF).

Note: Values for AWG #41 to #46 extrapolated from AWG #35 to #40 based on wire
gauge formula.

  17.5) What about stranded wire?

(From: Calvin Henry-Cotnam (cal@cate.ryerson.ca)).

In addition to the cross-section area, there are a few other factors.  First
off, a stranded wire effectively has more surface area than a solid wire of
the same gauge, but much of this surface is "inside" the wire.

I checked out the label of a spool of #18 stranded wire and found it was
comprised of 16 strands of #30 wire.  Given the info above that each reduction
of 3 in the gauge, then #18 has a cross-section area that is 16 times greater
than #30 -- so it *appears* to translate exactly.

Looking through a catalog for wire, I found that this more-or-less holds true,
though the occasional wire might have an extra strand or two.  Here is what I
quickly found -- there are many more, but this is a sample:

  17.6) Overall gauge Typical stranded wires made up of

            #32              7 x #40
            #30              7 x #38
            #28              7 x #36
            #26              7 x #34
            #24              7 x #32    19 x #36
            #22              7 x #30    19 x #34
            #20              7 x #28    10 x #30    19 x #32
            #18             16 x #30
            #16             19 x #29    26 x #30
            #14             41 x #30
            #12             65 x #30
            #10             65 x #28
             #8             84 x #27

Chapter 18) Items of Interest

Editor's note: Not all of these actually apply to small appliances but may
be of use nonetheless.

  18.1) Determining electricity usage

So, where does all the electricity (or money, same thing) go?

You could put a watt-hour meter on every appliance in your house but that is
probably not needed to estimate the expected electricity usage.

Check the nameplate on heating appliances or those with large motors.  They
will give the wattage.  Multiple these by hours used and the result is W-hours
(or KW-hours) worst case.  Appliances that cycle like refrigerators and space
heaters with thermostats will actually use less than this, however.

Multiple light bulb wattages by hours used to get the W-hours for them.

Things like radios, clocks, small stereos, etc., are insignificant.

Add up all the numbers :-).

It would be unusual for an appliance to suddenly increase significantly in its
use of electricity though this could happen if, for example, the door on a
freezer or refrigerator is left ajar or has a deteriorated seal.

  18.2) Taking equipment overseas (or vice-versa)

When does it make sense to take an appliance or piece of electronic equipment
to a country where the electric power and possibly other standards differ?

For anything other than a simple heating appliance (see below) that uses a
lot of power, my advise would be to sell them and buy new when you get there.
For example, to power a microwave oven would require a 2KVA step down (U.S.
to Europe) transformer.  This would weigh about 50 pounds and likely cost
almost as much as a new oven.

There are several considerations:

1. AC voltage - in the U.S. this is nominally 115 VAC but in actuality
   may vary from around 110 to 125 VAC depending on where you are located.
   Many European countries use 220 VAC while voltages as low as 90 or 100
   VAC or as high as 240 VAC (or higher?) are found elsewhere.

2. Power line frequency - in the U.S. this is 60 Hz.  The accuracy,
   particularly over the long term, is excellent (actually, for all intents
   and purposes, perfect) - better than most quartz clocks.  In many foreign
   countries, 50 Hz power is used.  However, the stability of foreign power
   is a lot less assured.

3. TV standards - The NTSC 525L/60F system is used in the U.S. but other
   countries use various versions of PAL, SECAM, and even NTSC.  PAL
   with 625L/50F is common in many European countries.

4. FM (and other) radio station channel frequencies and other broadcast
   parameters differ.

5. Phone line connectors and other aspects of telephone equipment may differ
   (not to mention reliability in general but that is another issue).

6. Of course, all the plugs are different and every country seems to think
   that their design is best.

For example, going to a country with 220 VAC 50 Hz power from the U.S.:

For electronic equipment like CD players and such, you will need a small
step down transformer and then the only consideration power-wise is the
frequency.  In most cases the equipment should be fine - the power
transformers will be running a little closer to saturation but it is
likely they are designed with enough margin to handle this.  Not too
much electronic equipment uses the line frequency as a reference for
anything anymore (i.e., cassette deck motors are DC).

Of course, your line operated clock will run slow, the radio stations
are tuned to different frequencies, TV is incompatible, phone equipment
may have problems, etc.

Some equipment like PCs and monitors may have jumpers or have universal
autoselecting power supplies - you would have to check your equipment
or with the manufacturer(s).  Laptop computer, portable printer,  and
camcorder AC adapter/chargers are often of this type.  They are switching
power supplies that will automatically run on anywhere from 90-240 VAC,
50-400 Hz (and probably DC as well).

Warning: those inexpensive power converters sold for international travel
that weigh almost nothing and claim to handle over a kilowatt are not
intended and will not work with (meaning they will damage or destroy)
many electronic devices.  They use diodes and/or thyristors and do not
cut the voltage in half, only the heating effect.  The peak voltage may
still approach that for 220 VAC resulting in way too much voltage on the
input and nasty problems with transformer core saturation. For a waffle
iron they may be ok but not a microwave oven or stereo system.  I also
have serious doubts about their overall long term reliability and fire
safety aspects of these inexpensive devices..

For small low power appliances, a compact 50 W transformer will work fine
but would be rather inconvenient to move from appliance to appliance or
outlet to outlet.  Where an AC adapter is used, 220 V versions are probably
available to power the appliance directly.

As noted, the transformer required for a high power heating appliance is
likely to cost more than the appliance so unless one of the inexpensive
converters (see above) is used, this may not pay.

For additional information, see the document: "International Power and
Standards Conversion".

  18.3) Controlling an inductive load with a triac

Thyristor based controllers need to be designed with inductive loads
in mind or else they may not work correctly or may be damaged when
used to control a motor or even a transformer or large relay.

There are a couple of issues:

1. Will it switch correctly?  Assuming it uses a Triac to do the switching,
   the inductive nature of the load may prevent the current from ever turning
   off.  Once it goes on the first time, it stays on.

2. Inductive kickback.  Inductive loads do not like to be switched off
   suddenly and generate a voltage spike as a result of the rapid change
   in current.  This may damage the Triac resulting the load staying
   on through the next millennium.

3. Heating.  Due to the inductive load, this will be slightly greater for
   the switch but I wouldn't expect it to be a major issue.  However, some
   derating would be advised.  Don't try to switch a load anywhere near
   the rated maximum for a resistive load.

Where feasible, adding a light bulb in parallel with the load will decrease
the effect of the inductance.  There is no way of knowing whether it will be
effective without analyzing the design or trying it.

Using a relay controlled by the Triac to then switch the inductive load
may work but keep in mind that a relay coil is also an inductive load - a
much smaller one to be sure - but nonetheless, not totally immune to these

  18.4) Dan's notes on low voltage outdoor lighting

(From: Dan Hicks (danhicks@millcomm.com)).

Most major brands of 12V lights are "sort of" interchangeable.
(Occasionally you have trouble getting the wire from one brand to
connect with the fixtures of another brand, but with a little fudging it
can usually be done.)  So look for the brand/model that gives you 
most of the lights you want in the styles you want, then augment with
add-ons from other brands.  Be aware of the current limit of 
transformers, though -- some kits have small transformers not sized for 
add-ons, while others have quite a bit of excess capacity.  I've got a 
(mostly) Toro system I'm semi-satisfied with, though the built-in
photocell system has failed twice.  (I'm going to install a separate
photocell & timer and just set the transformer to "On".)

  18.5) Effects of brownouts and blackouts on electronic equipment and appliances

Brownouts down to 100 V, maybe even 90 volts should not affect electronic
equipment.  It is possible that there is a no-man's land in between 0 and 90
volts (just an estimate) where strange things may happen.  Whether this will
cause permanent damage I cannot say.  The surge, spikes, and overvoltage
possibly associated with repeated brownouts or blackouts can damage
electronics, however.

Induction motors - the type in most large appliances - will run hotter
and may be more prone to failure at reduced line voltage.  This is because
they are essentially constant speed motors and for a fixed load, constant
power input.  Decrease the voltage and the current will increase to compensate
resulting in increased heating.  Similar problems occur with electronic
equipment using switching power supplies including TVs, some VCRs, PCs and
many peripherals.  At reduced line voltage, failure is quite possible.  If
possible, this type of equipment should not be used during brownout periods.

  18.6) Grounding of computer equipment

While electronic equipment with 3 prong plugs will generally operate properly
without an earth ground (you know, using those 3-2 prong adapters without
attaching the ground wire/lug), there are 3 reasons why this is a bad idea:

1. Safety.  The metal cases of computer equipment should be grounded so that
   it will trip a breaker or GFCI should an internal power supply short occur.

   The result can be a serious risk of shock that will go undetected until
   the wrong set of circumstances occur.

2. Line noise suppression.  There are RLC filters in the power supplies of
   computer and peripheral equipment which bypass power supply noise to
   ground.  Without a proper ground, these are largely ineffective.

   The result may be an increased number of crashes and lockups or just plain
   erratic wierd behavior.

3. Effectiveness of surge suppressors.  There are surge suppression components
   inside PC power supplies and surge suppression outlet strips.  Without a
   proper ground, H-G and N-G surge protection devices are not effective.

   The result may be increased hard failures due to line spikes and overvoltage

  18.7) Removing gummed labels (or other dried or sticky gunk)

My order of attack: water, alcohol, WD40, Windex, then stronger stuff like
ammonia, acetone, degreaser, flux-off, carburetor cleaner, lacquer thinner,
gasoline.  WARNING: most of these are flammable and harmful to your health -
use only in a well ventilated areas away from open flames.  Test that they
are safe for plastics and painted surfaces by trying some in an inconspicuous
location first.

(From: Paul Grohe (grohe@galaxy.nsc.com)).

I use "Desolv-it", one of those citrus oil (orange) based grease and 
"get's-the-kids-gum-out-of-your-carpet" cleaners (These are usually touted
as "environmentally friendly" or "natural" cleaners).

Spray it right on the label and let it soak into the paper for a minute or two,
then the sticker slips right off (it also seems to do well on tobacco and
kitchen grease residue).

The only problem is you have to remove the oily residue left by it. I just use
Windex (a window cleaner) to remove the residue, as I usually have to clean the
rest of the unit anyways.

(From: Bob Parnass, AJ9S (parnass@radioman.ih.att.com)).

I spray the label with WD40 and let it soak in for several minutes.  This
usually dissolves the glue without damaging the paint and I can remove the
label using my fingernail.

  18.8) Preventing radio frequency interference from whacking out appliances

This probably applies to many of the new high tech appliances including touch
lamps, smart irons and coffeemakers, etc.

(From: James Leahy (jleahy@norwich.net)).

My lamps were flashing each time I transmitted on 2 meters. HF
transmissions don't seem to cause any trouble. (that just knocks the
neighbor's TV out, har de har). Believe it or not, a simple snap-on
toroidal choke with the lamp cord wrapped as many turns possible near the
plug end cured it. Didn't want to bother with the several type of filter
circuits one could build to fix the problem. It may be a simple fix for
others with similar 2-way interference problems. One can get these chokes
at Radio Shack among other sources.

  18.9) Yard lights cycling and maintenance humor

(From: John Rowe (johnrowe@lightresource.com)).

The new maintenance man at one of our customers, a rather large apartment
complex in Minneapolis, had purchased from us a case of 200 watt incandescents.
He returned to our office about a week later with the lamps, complaining that
they 'flashed' and that the residents were really upset that these lights
(used outside) were not letting them sleep.

Under the 'customer is right' rule, I replaced them immediately, no questions
asked.  Of course I tested the 'bad' ones and found no defects.

When he returned with the new batch and the same complaint, he was really
upset, because the residents were now complaining to the management company
(his employer) about the situation.

I sat him down and asked him about the application.  He explained that they
were being used in 16" white poly pole lights, along all the footpaths around
the complex.

I asked how they were switched, and he replied that they used to be on timers
but that after complaints that the lights were on during the daylight hours,
he had purchased, from his local hardware store, screw-in photocells.  The type
into which the bulb screws.  These were then, inside the globes with the bulbs.

Of course the reflection within the poly globe was enough to prompt the
photocell to switch the circuit off and cycle the lights all night.

It took him a minute or two to comprehend his error.  I was able to recommend
an electrician to install more appropriate photocells.  He remained a good
customer for several more years after this incident.

My amusement comes from the picture I have in my mind of the residents of this
rather up-scale apartment complex looking out of their windows to see all the
walkway security lights going on and off all night, and wondering what the heck
was going on!  I imagine it was quite a sight.

  18.10) Will a hard-wired appliance save energy over a plugged in variety?

The resistance of the connection may be slightly lower - .05 versus .1
ohm, for example.  Other than the reduced amount of power lost in this
wiring, there is otherwise no functional difference.

With fancy expensive test equipment you might be able to detect it but
not in normal use.  The savings of a hard wired appliance would be quite
small even for a high wattage device like a space heater.

However, the hard wired connection will be more reliable and should not
deteriorate over time whereas a plug and outlet can corrode and the
spring force decreases with multiple plugins and outs.  The added resistance
will increase the losses.  So, in this regard, directly connecting the device
into the house wiring is better.

Note that if the cord and/or plug gets hot in use, this is a loss (though
for a space heater, the heat is just coming from the cord/plug instead of
the elements inside) - and a possible fire hazard as well and should be
checked out.  Sometimes, all it takes to remedy such a problem is to expand
the metal strips of the prongs of the plug so it makes better contact.

  18.11) A short history of heat

(From: Bill (bill394@juno.com)).

In the beginning we had but rocks and wood, not an efficient safe or practical
way to heat your home.  This system was refined and did do a fair job, as long
as you didn't mind cold spots or care about your safety.

Then we got more creative and used coal and then oil.  Oil was a far safer and
a better controlled system.  Then came gas now that's the fuel, the fuel of
choice for most.  It's also the one we are here to explain.

The older systems were really very simple.  You had a small pilot light which
was always on.  No safety, it just was lit, and we hoped it stayed lit.  When
the thermostat called for heat we opened a solenoid (electric valve) and
allowed gas to flow in and hopefully get lit by the pilot light.  If the pilot
had gone out the theory was that the majority of the gas would go up the
chimney and vent to the outside.  This simple system, used for years did a
fair job.  It lacked many features we take for granted today.

With the coming of more technology people started thinking more of safety and
expected more from there equipment.  A device commonly known as a thermocouple
was a great start in the direction of safety.  It is a union of dissimilar
metals that when heated generates electricity.  Now we had a way to stop gas
flow if our pilot went out.  By putting a solenoid in the pilot gas line we
could use a thermocouple to keep it powered open by the heat of the pilot.
Thus if our pilot went out the thermocouple would cool and stop producing
power to hold the solenoid open, gas flow would be interrupted.  Power from
this control was also required prior to the main valve opening, this making
uncontrolled gas flows a thing of the past.

With the coming of the R.E.A.  (Rural Electric Authority) power to every home
became a reality.  We now could introduce a new concept, blowers.  The fan
motor made forced air heat a reality.  Now even the most distant room could be
heated and even temperatures became a real happening.

The addition of electricity allowed for the addition of safety controls which
resulted in greatly reducing the fiscal size of a furnace.  We now had the
means to control running temperatures using the fan - turning it on and off by
the temperature and the on and off valve of the fire.  Should by chance the
fan not start, the furnace would over heat and a high temperature switch would
turn the fire off.  No melt down! very safe.

We all know that something simple that works well can't be left alone.  Man
just has to make it more labor complex.  Soon came the addition of some
actually neat ideas.  First being the addition of humidity, in cold climates a
must, that also lowers your heat bill.  The ability to run the fan just to
stir air, not add heat or cool.  Then the electronic air cleaner.  This one if
you have allergy is a must.  I don't have one so can't tell if it is on or
off.  BUT my son can tell in a matter of hours if its off.

And let's not forget the best of all air conditioning! In my world a must.
All of these additions were working steps towards our modern furnace.

The older burners were called ribbon (they sat in the combustion chamber) and
did a good job until we started going for higher efficiency.  Then a major
problem arrived, with colder heat exchangers came condensation.  This caused
the mild steel burners to rust and the size of the openings to get smaller,
making for a poor air to fuel ratio and just a terrible dirty burn, lots of
soot.  The good news is stainless steel burners did solve this, how ever it's
an expensive fix.

Now remember what we said about something that worked? You got it! new style
burners, not all bad though.  With the high efficiency furnaces comes a colder
stack temperature (fumes to chimney).  They are cold enough that they possibly
would not raise without a little help.  So a venter (blower) motor is used to
draw the fumes out of the heat exchanger and up the chimney.  This made
possible a new style burner.  It is in reality a far better burner then the
previous style.  We call it, in shot.  This burner is self adjusting for it's
air mixture and is positioned out side of the heat exchanger.  It is more like
the fire from a torch.  The fire is now sucked in to the heat exchanger by the
draft of the venter.  keep in mind the burner sits out in mid air.  In most
modern furnaces the heat exchanger is basically a piece of pipe with a burner
on one end and a venter on the other.

Knowing that good things get better, next we worked over the controls.  Rather
then using temperature to turn on the fan we use a solid state timer.  This
controls all fan functions.  Remember the pilot light?  It's gone.  We now use
either a hot surface igniter or if your lucky a spark.  The hot surface is
much like the filament of a light bulb.  It upon demand gets very hot and is
used as the source for ignition, unfortunately like a light bulb it burns out.
Again remember the thermal couple? Yes it to is gone.  We now use a micro
processor and electronically sense if the fire is lit.

On most modern furnaces the sequence of operation is as follows:

1.  The thermostat call for heat.  It starts only the venter.

2.  The venter comes to speed and if the chimney is not blocked and intake air
    is present it will draw a vacuum on the heat exchanger.  This is sensed by
    a vacuum switch, it now will turn on our timer.

3.  The timer lets the ignition come on and after a delay the gas valve opens
    and if all is well we finally get FIRE!

4.  A rod in the fire passes an extremely small current through the fire to
    ground.  If the microprocessor accepts the signal the fire will remain on.

5.  Our timer will soon turn on the blower.

When the thermostat no longer calls for heat:

Venter stops.  Vacuum is lost.  Fire is turned off.  Blower will run till
timer tells it to stop.  You still have the old style over temperature
switches.  All of this has made new furnaces extremely small, efficient and
safe.  Do they require more maintenance? YES.  If someone tells you different,
they tell less then the truth!  But I will gladly pay the cost to have my
family safe and comfortable.

Chapter 19) Service Information

  19.1) Wiring diagrams

Many larger appliances like washing machines and microwave ovens have
a wiring diagram or connection diagram pasted inside the cover.  However,
this is rare for small appliances.

In most cases, wiring is trivial and five minutes with your Mark I Eyeball(s)
and a pencil and paper (remember those?  If not, use your PC and a schematic
capture software package) will result a complete schematic.  There may still
be some uncertainties with respect to motor, transformer, or switch wiring
but testing with an ohmmeter or continuity checker should eventually prevail.

  19.2) Removing screw with stripped head

Even if a Phillips head screw head is severely damaged, it is sometimes
possible to free it just by applying enough pressure while turning with
a properly shaped screwdriver.  This can only be attempted if it is possible
to press hard without risk of breaking or damaging anything.

Other more drastic measures:

1. Drill it out - the same way you would remove a rivet - with a sharp
   twist drill bit on slow speed.  If necessary, use a metal or plastic
   sleeve to guide the drill bit.

2. Use a Dremel tool with a disk cutter or fine hacksaw blade to cut a slot
   in the head and then use a straight blade screwdriver to remove it.

3. Take a pair of sharp diagonal cutters and grip between the center and
   one edge or the entire head.  Or, grab the head with a pair of miniature
   locking pliers (Vice-Grips(tm)).

4. Drill a hole in the head and use a screw extractor (E-Zout(tm)).

Take care to avoid excessive mechanical shock to delicate equipment and avoid
allowing metal particles to fall into the interior of the appliance.

  19.3) Fil's tips on improvised parts repair

Whenever I'm stuck with some "Unprofitable" with a broken part,
I see if I can duplicate the functionality of the part. My
raw materials include:

5 minute 2-part epoxy (under $8 from a RC hobby store)
30 minute 2-part epoxy (under $8 from a RC hobby store)
wire: copper, steel, SS, "piano", spring, etc.
springs (a box of 1000s from hamfests, stripped monsters)
plastic stock: all types (you will learn which glue well)
plastic build up kit: two parts - foul smelling polymer and "dust"
Al stock: from thin foil to .080" to .5"
brain: regular edition :-)

As long as you know what the part does (you need not HAVE it...
as long as you can see where it goes in, what it moves, what
activates it, etc).

If it's something intricate, my parts bin door is NEVER closed..
and it gives it's "body" to science :-)

If you have part of the old plastic lever, it's usually easy to
build up the broken off part. I like to heat up a segment of
piano wire and insert it into the remaining part in such a way
as to hit the most "meat" of the part. Then, using either epoxy
or plastic build up material, I form something that does the job.

Overall, I have about a 75% "plastic broken part" repair ratio.
After a while, you will be able to judge if it's doable. "lever"s
are usually easy... sliding assemblies are a pain in the @ss...

  19.4) Fixing stripped plastic threaded holes

(From: Gordon S. Hlavenka (cgordon@worldnet.att.net)).

Simply set the screw on top of the hole, and press LIGHTLY on it with the tip
of your soldering iron.  The iron will heat the screw, which then slides into
the post.  After everything cools, you can take the screw out normally and the
threads are as good as new!  If the post is badly stripped, you may want to
stuff the hole with extra plastic shaved from some non-critical area to
provide additional material.

You have to be careful not to overheat, or push too hard.  But it works very

  19.5) Interchangeability of components

The question often arises: If I cannot obtain an exact replacement or
if I have another appliance carcass gathering dust, or
I just have some extra parts left over from a previous project, can I
substitute a part that is not a precise match?  Sometimes, this is simply
desired to confirm a diagnosis and avoid the risk of ordering an expensive
replacement and/or having to wait until it arrives.

For safety related items, the answer is generally NO - an exact replacement
part is needed to maintain the specifications within acceptable limits with
respect to line isolation (shock prevention) and to minimize fire hazards.
However, these components are not very common in small appliances.

For other components, whether a not quite identical substitute will work
reliably or at all depends on many factors.  Some designs are so carefully
optimized for a particular part's specifications that an identical
replacement is the way to return performance to factory new levels.  With
appliances in particular, may parts which perform common functions - like
thermostats - utilize custom mounting arrangements which precluded easy
substitution even if the electrical and thermal characteristics are an
exact match.

Here are some guidelines:

1.  Fuses - exact same current rating and at least equal voltage rating.
    I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm
    long fuse as a substitute.  Also, they should be the same type - slow
    blow only if originally specified.  A fuse with a faster response
    time may be used but it may blow when no faults actually exist.

2.  Thermal fuses and thermal cutouts - exact same temperature and current
    rating (if stated).  Physical size may also be important when these are
    buried in motor or transformer windings.

3.  Thermostats - temperature range must be compatible (or slightly wider
    may be acceptable).  Electrical current and voltage ratings must meet
    or exceed original.  With some devices, hysteresis - the tendency of
    a thermostat that has switched to stay that way until the temperature
    changes by a few degrees - may be an issue.  For example, electric
    heaters use a thermostat which has a typical hysteresis of 3-5 degrees F.
    However, heating appliances like waffle irons and slow cookers may depend
    on the thermal mass of the castings and use a thermostat with very little
4.  Resistors, capacitors, inductors, diodes, switches, trimpots, lamps and
    LEDs, and other common parts - except for those specifically marked as
    safety-critical - substitution as long as the replacement part fits
    and specifications are met should be fine.

5.  Rectifiers - use types of equal or greater current and PRV ratings.  A
    bad bridge rectifier can be replaced with 4 individual diodes.  However,
    high efficiency and/or fast recovery types are used in parts of electronic
    ballasts and other switching power supplies.

6.  Transistors and thyristors (except power supply choppers) - substitutes
    will generally work as long as their specifications meet or exceed those
    of the original.  For testing, it is usually ok to use types that do not
    quite meet all of these as long as the breakdown voltage and maximum
    current specifications are not exceeded.  However, performance may not
    be quite as good.  For power types, make sure to use a heatsink.

7.  Motors - small PM motors may often be substituted if they fit physically.
    Make sure you install for the correct direction of rotation (determined
    by polarity).  For universal and induction motors, substitution may
    be possible but power input, speed, horsepower, direction of rotation,
    and mounting need to be compatible.

8.  Sensor switches - some of these are common types but many seem to be
    uniquely designed for each appliance.

9.  Power transformers - in some cases, these may be sufficiently similar
    that a substitute will work.  However, make sure you test for compatible
    output voltages to avoid damage to the regulator(s) and rest of the
    circuitry.  Transformer current ratings as well as the current
    requirements of the equipment are often unknown, however.

10. Belts or other rubber parts - a close match may be good enough at least
    to confirm a problem or to use until the replacements arrives.

11. Mechanical parts like screws, flat and split washers, C- and E-clips,
    and springs - these can often be salvaged from another unit.

The following are usually custom parts and substitution of something from
your junk box is unlikely to be successful even for testing: SMPS (power
supply) transformers, microcontrollers, other custom programmed chips,
display modules, and entire power supplies unless identical.

  19.6) Appliance repair books

Your local large public or university library should have a variety of
books on appliance repair and general troubleshooting techniques.

Here are a few titles for both small and large appliance repair:

1.  Chilton's Guide to Small Appliance Repair and Maintenance
    Gene B. Williams
    Chilton Book Company, 1986
    Radnor, PA 19089
    ISBN 0-8019-7718-5

2.  Chilton's Guide to Large Appliance Repair and Maintenance
    Gene B. Williams
    Chilton Book Company, 1986
    Radnor, PA 19089
    ISBN 0-8019-7687-1

3.  Major Appliances, Operation, Maintenance, Troubleshooting and Repair
    Billy C. Langley
    Regents/Prentice Hall, A Division of Simon and Schuster, 1993
    Englewood Cliffs, NJ 07632
    ISBN 0-13-544834-4

4.  Major Home Appliances, A Common Sense Repair Manual
    Darell L. Rains
    TAB Books, Inc., 1987
    Blue Ridge Summit, PA 17214
    ISBN 0-8306-0747-1 (Paperback: ISBN 0-8306-0747-2)

5.  Home Appliance Servicing
    Edwin P. Anderson
    Theodore Audel & Co., A Division of Howard W. SAMS & Company, Inc., 1969
    2647 Waterfront Parkway, East Drive
    Indianapolis, IN 46214
    Telephone: 1-800-428-7267

6.  Handbook of Small Appliance Troubleshooting and Repair
    David L. Heisserman
    Prentice-Hall, Inc. 1974
    Englewood Cliffs, NJ 07632
    ISBN 0-13-381749-0

7.  Fix It Yourself - Power Tools and Equipment
    Time-Life Books, Alexandria, VA
    ISBN 0-8094-6268-0, ISBN 0-8094-6269-9 (lib. bdg.)

8.  Readers Digest Fix-It-Yourself Manual
    The Readers Digest Association, 1996
    Pleasantville, New York/Montreal
    ISBN 0-89577-871-8

    Overall, this is an excellent book which I would not hesitate to recommend
    as long as one understands its shortcomings.  The coverage of both small
    and large appliances, tools, and common yard equipment, as well as a
    variety of other categories of household repair (furniture, plumbing, etc.)
    is quite comprehensive.

    It is very well illustrated with hundreds upon hundreds of easy to
    understand exploded diagrams.  In fact, that is probably its most
    significant feature.  Where the equipment is similar to yours, it is
    possible to use the pictures almost exclusively for understanding its
    construction, operation, and disassembly/reassembly procedures.

    The discussion of each type of more complex equipment provides one or
    more troubleshooting charts.  Each entry includes the level of difficulty
    and identifies any needed test equipment (e.g., multimeter) for dealing
    with that problem or repair.

    However, this book is at best an introduction and once-over.  Much of the
    material is presented based on one or two models of a particular type of
    devices while sort of implying that all the rest are similar.  In all
    fairness, very often this is sufficient as most models of simpler differ
    only in details.  However, for all but the most general repairs on the
    more complex appliances, a book with more specific information would be
    highly desirable before actually tackling the repair.

    One significant shortcoming is that there are NO wiring diagrams of any
    kind for any of the appliances.  Their approach seens to be to just check
    parts for failure.  While this will be successful in many cases. a wiring
    diagram would be useful when explaining appliance operation and would
    help in logical troubleshooting to localize the problem.

    Although there is a chapter on home electronics - audio, video, computer,
    security systems, etc. - don't expect anything useful beyond very general
    information and simple repairs like replacing belts and looking for bad
    connections.  While it isn't surprising that the treatment of this complex
    equipment is superficial at best in a book of this type, in some cases it
    is as though the editing was based on a page limit rather than including
    a more complete summary but with fewer details.  For example, the only
    repair on a CD player beyond belts and lens cleaning is to test and replace
    the tray loading motor (one particular model).  Unfortunately, some of the
    specific information is not entirely accurate either and may be misleading
    and expensive.  The safety instructions for the electronics (as well as
    microwave ovens) is also a bit lacking considering some of the suggestions
    for troubleshooting and parts replacement.

    Some errata: Testing of microwave oven HV diodes (good ones will test bad),
    HV discharging of TVs and monitors always (not needed) and possibly to
    wrong place (should be to picture tube ground, not chassis ground) but no
    mention of power supply capacitor discharging, not specific enough on
    'good' and 'bad' resistance readings for various parts like motors.

9.  All About Lamps - Construction, Repair, Restoration
    Frank W. Coggins
    Tab Books, 1992
    Blue Ridge Summit, PA 17214
    ISBN 0-8306-0258-5 (hardback), 0-8306-0358-1 (paperback)

10. How to Repair and Care for Home Appliances
    Arthor Darack and the Staff of Consumer Group, Inc.
    Prentice-Hall, Inc. 1983
    Englewood Cliffs, NJ 07632
    ISBN 0-13-430835-2 (hardcover), ISBN 0-13-430827-1 (paperback)

11. Popular Mechanics Home Appliance Repair Manual
    Hearst Books, NY, 1981
    ISBN 0-910990-75-1

12. Microsoft Home (CDROM)
     Based on the Readers Digest Complete Do-It-Yourself Guide
     The Readers Digest Association, 1991
    Microsoft, 1996
    ISBN 0-57231-259-9

    This isn't the Fix-It-Yourself Manual but I expect that is coming on CDROM
    if it is not out already.  However, there is some information including
    nice diagrams relating to door chimes, telephone wiring, incandescent and
    fluorescent lighting fixtures, electrical switches, and heating and air
    conditioning systems (in addition to everything else you ever wanted to
    know about how your house works, tools and tool skills, materials and
    techniques, and home repair and maintenance).

  19.7) Large appliance repair manuals and Web assistance

These appliance repair manuals are supposed to be written specifically
for the do-it-yourselfer.  Manuals are currently available for about
$20 each for washing machines, clothes dryers, dishwashers, refrigerators,
and ovens and cooktops:

* EB Large Appliance Repair Manuals via Internet
  Email: info@appliancerepair.net
  Phone: U.S. (toll-free) 888-974-1224, Canada, 714-974-1224
  Web: http://www.appliancerepair.net/manuals.htm

They may be available from your local appliance parts dealer for even less.
The web site has a list of parts dealers organized by telephone area codes
(though it does not appear to be very comprehensive at the current time).

There are several web sites devoted to large appliance repair.  Here are two:

* Appliance Clinic, http://www.phoenix.net/~draplinc/

  Tips (often by manufacturer/model) for clothes washers, dryers, and
  refrigerators/icemakers.  Also, some parts other info, free email replies.

* Garrell's Appliance Center, http://members.tripod.com/~garrellsappliance/#Index

  Washers, dryers, stoves, ovens, refrigerators, air conditioners.  Parts,
  manufacturers, manuals, free email replies.

  19.8) Manufacturer support

Major manufacturers may provide a variety of types of support for their
products including technical assistance, parts sourcing, unadvertised repair
or replacement beyond the expiration of the warranty, upgrade or replacement
to fix known defects whether covered by official recalls or not, etc.

I have on several occasions been pleasantly surprised to find that some
companies really do stand behind their products and all it took was a phone
call or short letter.  One only hears of the horror stories!

(From: lizard3 (lizard3@ix.netcom.com)).

Sears sells schematics and plans of all their appliances. This includes a
breakout of the entire machine with each part number. They have a toll-free
number to call. All you need is the model number and a credit card.  We have
used their washing machine schematic a couple of times to replace some very
minor parts.

  19.9) Parts suppliers

Common parts like cordsets, plugs, wire, and some light bulbs can be found
a larger hardware stores, home centers, or electrical supply houses.  Small
electronic components like resistors and capacitors, can be found at any
electronics distributor - including even Radio Shack in a pinch.

The original manufacturer of the appliance is often the best source for
unusual or custom parts.  Many are quite willing to sell to the consumer
directly.  Check for an 800 number and have complete information on model
and a part number if possible.  However, their prices may be high - possibly
rendering a repair uneconomical.

There are numerous appliance repair centers that may be able to obtain parts
at lower cost - check your Yellow Pages.  Their prices may be less than half
of those of the original manufacturer.

The following is a good source for consumer electronics replacement parts,
especially for VCRs, TVs, and other audio and video equipment but they
also carry a variety of common electronic components and appliance parts
like switches, range elements, defrost timers, light bulbs, and belts

* MCM Electronics                 (VCR parts, Japanese semiconductors,
  U.S. Voice: 1-800-543-4330.      tools, test equipment, audio, consumer
  U.S. Fax: 1-513-434-6959.        electronics including microwave oven parts
                                   and electric range elements, etc.)
  Web: http://www.mcmelectronics.com/

Also see the documents: "Troubleshooting of Consumer Electronic Equipment" and
"Electronics Mail Order List" for additional parts sources.

Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]