Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff


[Document Version: 2.86] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff

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) Why is all that junk in your attic?

If you have ever tried to get a piece of consumer electronic equipment
repaired, you understand why so much dead 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 Walkman 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 answering machine.  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 boombox to take take to
the beach may just make sense after all.

This document provides maintenance and repair information for a variety
of consumer electronic devices not covered 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.  As most difficulties encountered with this type of equipment are
mechanical, there is significant emphasis on dirt, lubrication, deteriorated
rubber parts, broken doohickies, and so forth.  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 - or decide that replacement
is indeed the better option.  However, in many cases, you will be able to do
what is required to repair a piece of equipment for a fraction of what would
be charged by a repair center.  Perhaps, you will even 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)!

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.  It will also be easier to do
further research using a repair book or guide.  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 new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.

If you are just getting started, you should refer to "Repair Briefs, an
Introduction" for additional troubleshooting tips, recommended test
equipment, suggested parts inventory, and other general information.

  2.2) Information on consumer electronics technology

Your local public library (621.384 if your library is numbered that way)
or technical bookstore represents a valuable resource for books on both
the technology and repair of a large variety of consumer electronics

For general troubleshooting techniques, see the section: "Some general references".

  2.3) Web sites dealing with low voltage wiring

These sites deal with non-power wiring information: phones, audio, video,
home automation, etc.  Since much of the content of this document relates
to home electronics that may involve such wiring, these sites may be of
interest.  The first also has a pile of links to other related sites.

* http://www.mcdata.com/~meh0045/homewire/wire_guide.html
* http://www.geocities.com/SiliconValley/Pines/4116/
* http://www.geocities.com/ResearchTriangle/3300/
* http://us016757.home.mindspring.com  (Engineering Notebook section)

Chapter 3) Maintenance and Troubleshooting Guide

  3.1) SAFETY

The only danger to you in most of these devices is the AC line connection
(if any) and getting sucked into any mechanical people traps.  Before you
plug in the unit with any covers removed, make note and cover up any
exposed AC line connections.  The rest of the circuitry is low voltage
and while you can destroy your equipment by your actions, you should be
fairly safe.  Exceptions to this are noted where appropriate.

However, you never can tell where an exciting troubleshooting
expedition will lead.  The following Safety Guidelines are included
for your survival when working on line connected or high voltage
equipment (and your reading enjoyment).

  3.2) Safety guidelines

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.

The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions.  Repair of TVs, monitors,
microwave ovens, and other consumer and industrial equipment 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: TVs and monitors may use parts of the metal chassis
  as ground return yet the chassis may be electrically live with respect to the
  earth ground of the AC line.  Microwave ovens use the chassis as ground
  return for the high voltage.  In addition, do not assume that the chassis
  is a suitable ground for your test equipment!

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

* 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 20K-100K ohm resistor).  Monitor while discharging and/or verify that
  there is no residual charge with a suitable voltmeter.

* For TVs and monitors in particular, there is the additional danger of
  CRT implosion - take care not to bang the CRT envelope with your tools.
  An implosion will scatter shards of glass at high velocity in every
  direction.  There is several tons of force attempting to crush the typical
  CRT.  Always wear eye protection.

* 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.

* 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.

* Perform as many tests as possible with power off and the equipment unplugged.
  For example, the semiconductors in the power supply section of a TV or
  monitor can be tested for short circuits with an ohmmeter.

* 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 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.  A circuit breaker is too slow and insensitive to provide any
  protection for you or in many cases, your equipment.  The GFCI may protect
  your scope probe from smoking if you accidentally connect its ground 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!

  3.3) Troubleshooting tips

Many problems have simple solutions.  Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures.  For a tape deck, it may just be a bad belt or a bad tape.
Try to remember that the problems with the most catastrophic impact on
operation (a dead AC adapter) have the simplest solutions (repair the
wires broken due to flexing in the power cable).

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).

Whenever working on precision equipment, make copious notes and diagrams.
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 for storage.

Another consideration is ESD - Electro-Static Discharge.  The electronic
components in a some devices like cassette decks, Walkmen, and portable
phones, are vulnerable to ESD.  There is no need to go overboard but taking
reasonable precautions like not wearing clothing made of wool that tends
to generate static.  When working on larger devices like cassette decks, get
into the habit of touching a ground like the metal chassis before touching
any circuit components.

A basic set of precision hand tools will be all you need to disassemble
and perform adjustments on most consumer electronics equipment.  These
do not need to be really expensive but poor quality tools are worse than
useless and can cause damage.  Needed tools include a selection of Philips
and straight blade screwdrivers, needlenose pliers, wire cutters, tweezers,
and dental picks. A jeweler's screwdriver set is a must particularly if you
are working on compact equipment.  For adjustments, a miniature (1/16" blade)
screwdriver with a non-metallic tip is desirable both to prevent the
presence of metal from altering the electrical properties of the circuit
and to minimize the possibility of shorting something from accidental
contact with the circuitry.

For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'
(they are the same) and a heat gun or blow dryer come in handy to identify
components whose characteristics may be drifting with temperature.  Using the
extension tube of the spray can or making a cardboard nozzle for the heat
gun can provide very precise control of which components you are affecting.

For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs,
an Introduction" as well as other documents available at this site.

  3.4) Soldering equipment

The ease and quality of your work will depend both on proper soldering as
well as desoldering (often called rework) equipment.

* A low wattage (25 W) iron for delicate components including discrete
  semiconductors, ICs, other small parts).

* A medium wattage (40-50W) iron for heavy duty circuit board work including
  power components, power plane connections, and large transformers).

* A 100-140 W soldering gun for chassis connections.

Three wire grounded soldering equipment is recommended but I do not consider
it essential for this type of repair work.  However, a temperature regulated
soldering station is a really nice piece of equipment if you can afford it or
happen on a really good deal.

I consider fine gauge rosin core solder (.030 or less) to be best for most
applications (e.g., Ersin Multicore).

* Desoldering pump - SoldaPullit or similar 'solder sucker' for removing
  components easily and usually nondestructively.  SolderWick is also
  handy for cleaning up desoldered connections.

A vacuum rework station is not needed unless you are removing your soldered
in 500 pin Intel P6!

  3.5) 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!

  3.6) 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.

  3.7) 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.

  3.8) Test equipment

Don't start with the electronic test equipment, start with some analytical
thinking.  Many problems associated with consumer electronic equipment
do not require a schematic (though one may be useful).  The majority
of problems with consumer electronics equipment are mechanical and can be
dealt with using nothing more than a good set of precision hand tools; some
alcohol, degreaser, contact cleaner, 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.

A DMM or VOM is necessary for checking of power supply voltages and
testing of sensors, LEDs, switches, and other small components.  This does
not need to be expensive but since you will be depending on its readings,
reliability is important.  Even a relatively inexpensive DMM from Radio
Shack will be fine for most repair work.  You will wonder how you ever
lived without one!  Cost: $25-50.

Unless you get deep into electronic repair, a high bandwidth oscilloscope
is not required.  However, a relatively inexpensive 5 or 10 MHz dual trace
scope is very handy and you will find all kinds of uses for it.  Such a
scope should cost less than $150 on the used market.

There are several specific pieces of test equipment that you may already own
which are required depending on the devices being fixed.

Audio equipment:

* Stereo tuner or other audio signal source.  An audio signal generator 
  is nice but not really essential.

* An audio amp connected to a loudspeaker.  The input should be selectable
  between line level and mic level and be brought out through a shielded
  cable to a test probe and ground clip.  This is useful for tracing
  an audio circuit to determine where a signal is getting lost.  Inexpensive
  signal tracers are also available but this option is likely free.

* Prerecorded and garbage cassettes or tapes for testing of component
  and walkman tape transports.

Video games, cable boxes, and other video sources:

* A TV (preferably color) with RF (antenna) inputs connected to a VCR
  with a working tuner and RF modulator or a TV with both RF and A/V (RCA
  jacks) inputs.

* A known good game cartridge to confirm that the problem is in the game

Telephone equipment:

* A working tone dialing phone.  If I had a choice, it would be a good
  old reliable ATT Touch Tone desk phone.

* A dual connector phone jack.  Two independent phone lines are desirable
  for answering machine or modem testing.

* A PC or laptop with a fax-modem (for modem and fax machine testing).

* A low voltage DC power supply or wall wart to perform certain tests
  without a telephone connection or phone line simulator.

* A handy-dandy phone line tester.  The inexpensive variety is just a pair of
  LEDs in series with a resistor for each line attached to an RJ11 connector.
  However, this is much more convenient than fumbling with a multimeter!  You
  can buy one at Radio Shack (about $7) or easily build your own.  See the
  section: "Handy-dandy phone line tester" for details.

  3.9) Handy-dandy phone line tester

This simple device (total cost about $3) will show at a glance the status of
all of the phone lines connected to a modular jack.

Parts list: Surface mount RJ11 modular jack, RJ11 extension cord.
            For each phone line: 2 LEDs (red and green), 10K resistor.

Construct the following circuit for each line and attach to the appropriate
color terminals/wires of the modular jack:

                           10K            Green LED
Line 1:     (Green) o------/\/\-----+--------|>|-------+------o (Red
Line 2:     (Black)                 |  Wiring Correct  |        (Yellow)
Line 3:     (White)                 |                  |        (Blue)
                                    |      Red LED     |
                                      Reverse Polarity

Note: Polarity of Tip and Ring are reversed with respect to the wire colors
because of swap that occurs using the RJ11 extension cord.

Mount the LEDs in holes drilled in the plastic cover of the modular jack
(making sure they clear the base when the cover is screwed down).

To test old style 4 prong phone jacks, use an adapter on the end of the RJ11
extension cord.

Correctly wired lines will light up green, reverse polarity will be red, dead
line will be dark, line-in-use will be dark or nearly dark.  If you catch a
line that is ringing. both LEDs will flicker.

Putting just the LED portion (leave out the resistor) of this circuit in
*series* with the phone line will implement an off-hook (in use) indicator.

  3.10) Getting inside consumer electronic equipment

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

Note: the sections on loudspeakers, cameras, and watches have additional
'getting inside' info.

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 or cassette compartment is opened or a trim panel is popped off.

   These will often be of the Philips variety.  (Strictly speaking, many
   of these are not actual Philips head screws but a slight variation.
   Nonetheless, a Philips screwdriver of suitable size will work on them.)
   A precision jeweler's  screwdriver set including miniature Philips
   head drivers is a must for repair of miniature portable devices.

   Sometimes, you will find Torx or a variety of security type fasteners.
   Suitable driver bits are available.  Sometimes, you can improvise
   using regular tools.  In the case of security Torx, the center post can
   usually be broken off with a pair of needlenose pliers allowing a normal
   Torx driver to be used.  In a pinch, a suitable size hex wrench can
   substitute for a Torx driver.   Places like MCM Electronics carry a
   variety of security bits.

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.

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!

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.  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.

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

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

Do not be tempted to use compressed air!

I would quicker use a soft brush to carefully dust off the circuit boards and
power supply.  Work in such a way that the resulting dust does not fall on
the mechanical parts.

For intricate mechanisms, using compressed air could dislodge dirt and dust
which may then settle on lubricated parts 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 surfaces of the deck (in addition to
the normal proper cleaning procedures for the guides, rollers, heads,
wheels, belts, etc.)

  3.12) What to do if a tiny tiny part falls inside

We have all done this: a tiny washer or spring pops off and disappears
from sight inside the guts of the unit.  Don't panic.  First - unplug it
if AC powered.  Remove the battery pack if possible from a portable device.

Try to locate the part with a bright light without moving anything.  You may
have gotten lucky (yeh, right).  Next, over an area where a dropped part
will be visible (not a shag carpet!), try any reasonable means to shake
it loose - upside down, a little gently tapping and shaking, etc.  A hard
surface is better in some ways as you might hear the part drop.  On the
other hand it may bounce into the great beyond.

If this does not work, you have two options:

1. Assume that the part has landed in a place that will not cause future
   problems.  There could be electrical problems if it is metallic and shorts
   out some circuitry or there could be mechanical problems if it jams some
   part of the mechanism.  There is an excellent chance that the part will
   never cause any harm.  What chance?  I don't know, maybe 99%.  It is not
   worth taking the unit to pieces to locate the part.  You are more likely to
   damage something else in the process.  Obtain a replacement and get on
   with your life.  The exception is, of course, if you now begin experiencing
   problems you **know** were not there before.

2. Take the unit to pieces in an attempt to locate the part.  For all you
   know, it may be clear across the room and you will never find it inside.
   If all the gymnastics have not knocked it loose, then it may be really
   wedged somewhere and will stay there - forever.  If the unit behaves
   normally, then in all likelihood it will continue to do so.

To prevent this sort of thing from happening in the future you will no doubt
be much more careful.  Sure you will!  Some suggestions to prevent ejection
of an E-clip, split washer, or spring into the great beyond:

* Construct a paper dam around the area.

* Tie a thread or fine wire around the part before attempting to remove it.
  Keep this 'safety line' on until after it has been reinstalled, then just
  pull it free.

* Keep one finger on the part as you attempt to pop it free.

* Hold onto the part with a pair of needlenose pliers or tweezers while prying
  with a small screwdriver.

Chapter 4) Audio Cassette and Open Reel Tape Equipment

  4.1) Parts of an audio tape transport

The following description applies to most cassette and open reel tape
transports including those used in portable and microcassette recorders,
Walkmen, and telephone answering machines.

Looking at the top of the deck such that the tape heads are at the bottom:

* Supply reel table - left hand side platform on which the supply tape reel
  sits.  Edge which contacts idler tire (if used) should be cleaned.

* Takeup reel table - right hand side platform on which the takeup tape reel
  sits.  Edge which contacts idler tire (if used) should be cleaned.

* Idler - assembly which swings between supply and takeup reels and transfers
  power to the appropriate reel to wind the tape up during play and record
  and often to drive FF and REW.  In some designs, this uses gears or some
  other type of mechanism.  In very expensive decks, individual motors are
  used for each reel and there is no intermediate drive.

* Idler tire - the black rubber ring on the outside of one part of the idler
  which actually contacts the reel edges.  This is not as common in audio
  tape decks as VCRs.  If one is used, it should be cleaned and inspected
  for deterioration, dirt, and wear.

* Capstan - right side after tape exits from area of record/playback/erase
  heads.  The capstan is a shaft (about 1/16" diameter in cassette decks,
  recorders, and Walkmen, 3/16" or larger diameter in open reel machines)
  which during play and record modes precisely controls tape movement when
  the pinch roller is pressed against it.  For autoreverse transports,
  there will be two capstans - one on each side of the head assembly
  so that the tape is always pulled across the heads as this is most
  precise.  (In a VCR, there is only one capstan and it is also used for
  reverse play or search modes.)  Clean to assure proper tape movement
  during play and record modes.

* Pinch Roller - black rubber roller which spins freely and is pressed
  against the capstan during play, record, and search modes.  For autoreverse
  decks, there will be two pinch rollers, one for each capstan.  A hard,
  shiny, cracked, or dried out pinch roller can lead to tape edge munching
  and erratic or wavering sound.  Clean thoroughly (until no more black
  stuff comes off).  Inspect for cracked or deteriorated rubber.

* Tape heads.  Most low to mid priced tape decks have two - an erase head
  and a combined record/playback head.  High-end decks will have separate
  record and playback heads supporting sound-on-sound mixing to the same track
  and allowing recording quality to be monitored off of the tape.  These may
  be physically independent assemblies or combined into a single unit.
  Autoreverse decks often have a head assembly that rotates 180 degrees
  depending on tape direction.  This is less expensive than having two erase
  heads and two record/playback heads or a single record/playback head that
  shifted position to align with the appropriate tracks and electronic
  switching of the record and playback signals.

  Play-only transports such as found in car cassette decks and Walkmen
  do not need an erase head.  Autoreverse play-only decks often do just shift
  the position of the playback head a fraction of a mm depending on playback
  direction to line up with the tracks and interchanges the connections
  for L and R channels.

  Clean the polished surfaces thoroughly (DO NOT use anything abrasive!).

* Various other guide posts - vertical stationary metal posts which tape
  contacts.  Should be cleaned but rarely need adjustment.

* Belts - various size black rubber bands - a typical transport will have
  between 0 and 4 belts, usually below decks.  These will require
  replacement after a few years.  Clean and inspect.

  4.2) General guide to tape deck cleaning and rubber parts replacement

The following procedures apply to boom boxes, cassette decks, microcassette
and other portable tape recorders, open reel tape decks, and telephone
answering machines.  While the tape transports used in these devices are
less complex than those used in VCRs and other helical scan recording
equipment, some routine maintenance can go a long way towards preventing
future problems.  All the guideposts, wheels, and rubber parts should be
inspected and cleaned periodically - how often depends on usage.  Of course,
no one really does this unless something goes wrong.

Qtips and alcohol (91% medicinal is ok, pure isopropyl is better. Avoid
rubbing alcohol especially if it contains any additives) can be used
everywhere EXCEPT on the rotating heads of VCRs and camcorders (and other
helical scan devices like 8mm and 4mm (DAT) storage drives) - see the
document: "Notes on the Troubleshooting and Repair of Video Cassette Recorders" for detailed procedures on cleaning of video heads - you can
destroy the most expensive part of your VCR by improper cleaning techniques.
Dry quickly to avoid leaving residue behind.  Sometimes good old fashioned
water (just a damp cloth) will work better on sugar based gunk and other
kids' grime.

Cleaning may get your machine going well enough to get by until any replacement
rubber parts arrive.

Things to clean:

(Some of these components may not be present in your particular equipment).

1. Capstan and pinch roller.  These collect a lot of crud mostly oxide which
   flakes off of (old) tapes.  Use as many Q-tips (wet but not dripping
   with alcohol) as necessary to remove all foreign matter from the capstan
   (the shiny shaft that pulls the tape through the unit for play and record).
   Just don't get impatient and use something sharp - the crud will come off
   with the Qtips and maybe some help from a fingernail.  On autoreverse
   decks, there will usually be two capstans and pinch rollers.

   Clean the pinch roller (presses against the capstan in play and record)
   until no more black stuff comes off.  Use as many Qtips as necessary.

   If the pinch roller is still hard and/or shiny or has a cracked surface,
   it will probably need replacement.  Many are available from the sources
   listed in the section: "Recommended parts suppliers".

2. Various guideposts that the tape contacts.  Clean like the capstan.

3. Idler tire (idler swings between reels and transfers motor power to
   reels - clean until no more black stuff comes off.  A dirty or worn idler
   tire may prevent the takeup reel from turning resulting in spilled tape.

   Also, the idler assembly includes a slip clutch.  If this weakens, the
   idler may not have enough force to press on the reel table edges.

4. Reel table edges - surface on the reel tables where the idler contacts.

5. Audio head(s) and erase head.  Q-tips and alcohol are ok for these.
   Do not use anything sharp or abrasive!

6. Anything else that the tape contacts on its exciting journey through your

7. Rubber belts.  Access to some of these may require the services of a
   Swiss watchmaker (if any still exist).  Some boomboxes seem to be designed
   specifically to be difficult to service.  After noting where each belt
   goes, remove them individually (if possible) and clean with alcohol and
   Qtips or a lint free cloth.  Dry quickly to avoid degrading the rubber
   from contact with the alcohol.  If a belt is trapped by some assembly
   and not easy to remove, use the Qtip on the belt and/or pulley in place.
   However, if it is stretched, flabby, or damaged, you will need to figure
   out how to free it.

   Note that on some equipment like dual cassette boomboxes and telephone
   answering machines, the belt(s) may follow a highly circuitous path -
   make a detailed diagram!

   Any belts that appear loose, flabby or do not return instantly to
   their relaxed size when stretched by 25% or so will need to be replaced
   and may be the cause of your problems.  Belts cost about $.30-$2.00.
   Meanwhile, the belts will function better once they are cleaned, maybe
   just enough to get by until your replacements arrive.

  4.3) Lubrication of 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.

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 capstan, 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!

  4.4) Tape head demagnetizing

With audio tape decks, demagnetizing is often recommended to improve
sound quality and frequency response.  There is some debate as to
how much benefit there is to this practice but if done properly,
there is little risk.  Demagnetizing removes the residual magnetic
fields that can build up on ferrous pole pieces of the tape heads and
various guideposts and other parts in the tape path which may affect
frequency response.

Use a small demagnetizer designed for a tape deck or cassette deck.  See
the section: "Homemade audio tape head demagnetizer" if you don't have one
or don't want to buy one.  However, do not use anything that might be too
powerful or a bulk tape eraser which would certainly be too powerful.

Make sure the tip is covered with a soft material to prevent damage to
the finely polished surfaces in the tape transport.

Turn power on to the demagnetizer when a couple of feet away from the unit.
Then, slowly bring it in close and slowly go over all surfaces of anything
that the tape contacts or comes close to in the tape path.  The key
word here is **slowly**.  Move fast, and you will make the magnetic
fields stronger.  When finished, slowly draw the demagnetizer away to a
distance of a couple of feet before turning it off.

  4.5) Homemade audio tape head demagnetizer

A perfectly serviceable tape head demagnetizer can be easily constructed
using a large nail, 100 turns of insulated wire (just guessing here) and
an AC wall adapter (from an obsolete modem, for example).  Grind down the
end of the nail so that it is not sharp and coat it with a soft material
or cover the end with electrical tape to protect the finely polished heads
from scratches.

Adjust the number of turns and input voltage for desired strength.  How
strong should it be?  A direct comparison with a commercial unit would be
best but when in close proximity to a steel surface, you should be able to
feel the 120 Hz attraction but it shouldn't jump out of your hand!  Sort of
like "Use a pinch of salt you will know how much" :-)

  4.6) Building a bulk tape eraser

A variety of approaches work for this - all based on strong magnetic fields.
These will erase floppy diskettes, audio and video tapes, and all your credit
cards and Turnpike passes!

* Magnets removed from large loudspeakers (including the pole pieces where
  the voice coil went) and microwave oven magnetrons.

* Some motors, transformers, the butt-end of some soldering guns, etc.

(From: Steven L. Bender (buqu35d@prodigy.com)).

You need a Power Transformer about 3" in each direction, can be like a 
low voltage 12 volt / 3 Amp unit or rated higher.  Remove end bells if 
any, remove all the metal laminations (break the first one, yank it, 
and the rest will come easier).  Re-insert all the metal laminations 
facing in the same direction, with the "E" all pointed the same, 
re-glue, varnish, or whatever.  Connect AC Plug to the Primary, then 
insulate the whole works with Plastic tape and outre layer of Duct 
tape. After insulating it with several layers of tape - Instant Bulk 

Warning - Do not apply power for more than 60 seconds at a time!  (It will get
hot and burn your hand after two minutes.)

I had one of those for some years, but accidentally left it plugged in, 
(pulled the wrong wire out of the 6 to 1 outlet box) and after a few 
minutes, it smelled and was too hot to touch, and made a nasty noise as 
the copper started to melt...  (Sounds Effects of Liquid Krell Metal
in the distance...., Forbidden Planet - Paramount, 1956).

Luckily I didn't walk out, another few minutes and it would have caught fire..

I am not liable for any personal, profession, or consequential damages from
use of this information !!!

  4.7) Splicing of audio tapes

If a tape is broken or seriously crinkled, cutting out the bad section and
joining the remaining ends will be necessary.  There are special splicing
kits for this.  I don't know if a place like Radio Shack carries these but
an audio dealer or electronics distributor should have one.    In a pinch, you
could very carefully use a razor blade or Xacto knife to cut the tape an a
45 degree angle and ordinary transparent to mend it.  Then, it is best to copy
the tape to a new one.  At least with an audio deck, you don't really have to
worry about ruining the heads with an improperly made splice though you do
want to avoid depositing adhesive from the mending tape onto parts of the

  4.8) Tape or cassette deck, recorder, or Walkman transport problems

The following are common problems with audio tape transports:

1. No movement in PLAY or REC - most likely capstan is not turning or not
   engaged.  If the motor is not working (listen for a hum from inside the
   transport), refer to the chapter: "Motors and Relays".  Otherwise, see
   the list below.

2. Tape eating - the capstan is turning but the takeup reel is stationary
   or not turning rapidly enough to take up the tape as it feeds from the
   capstan/pinch roller.

2. FF and/or REW are inoperative or sluggish - assuming the motor is working,
   the driven reel is not being powered at all or does not have sufficient
   torque to overcome the tape friction.  The driven reel alone must
   pull the tape through the transport.

Note that the required torque for the driven reel is much less for PLAY
and REC compared to FF and REW as the capstan in contact with the pinch
roller pulls the tape from the supply reel.

The most likely causes are similar for all of these symptoms.  The driven
reel and/or capstan is not turning due to:

* A broken or stretched belt, an old and deteriorated, dirty, or worn idler
  tire.  Refer to the section: "General guide to tape deck cleaning and rubber parts replacement".

* Worn or broken.  For example, a spring may have popped off an idler clutch
  or a press-fit gear or pulley may have split.

* Gummed up lubrication which is preventing the idler gear or tire that
  operates the takeup reel from engaging.  See the section: "Lubrication of electronic equipment".

* A solenoid that is not engaging properly due to a weak spring, insufficient
  drive, or lubrication problems.

If the cause is not immediately evident once the bottom of the transport
is visible, try to observe exactly what is happening when you play a
garbage tape or run the deck with no tape present.  Look for broken parts
or bits of parts that may have failed off.

If the transport shuts down shortly after entering any mode, check for
a missing or stretched tape counter drive belt or a defective reel
rotation sensor.  The tape eating protection circuits are shutting
down the unit improperly due to a lack of reel sensor pulses.  A related
symptom will be that the tape counter (mechanical or electronic) does not
change during the period when the tape is moving.

If the logic is not properly controlling the various solenoids or other
actuators in a 'soft touch deck', then a service manual will be needed
to proceed much further.

  4.9) Tape transport azimith adjustment

When prerecorded tapes or tapes recorded on another deck sound muddy, the
azimith alignment of the suspect deck may have shifted or be misadjusted.
Azimith refers to the angle that the record/playback head gap makes with
respect to recorded audio tracks.  This angle should be exactly 90 degrees.
If it is not, than high frequencies will tend to be reduced in amplitude
during playback of a tape not recorded on this machine.  Similarly, a tape
recorded on a transport with an improper azimith setting will sound muddy
on a properly adjusted deck.

A simple test to determine if azimith alignment is your problem is to
record some music on your machine and immediately play it back.  If this
recording sounds fine but it sounds muddy on another deck, then improper
azimith alignment is the likely cause.

If the recording is still muddy, your deck may have electronic problems
like excessive bias (check to make sure you have selected the proper type
of tape or bias setting), a worn record/playback head, or the heads or
other parts may be magnetized (see the section: "Tape head demagnetizing".,
However, dirty heads as well other mechanical problems can also result in weak
muddy sound.  See the section: "General guide to tape deck cleaning and rubber parts replacement".

The best way to adjust azimith is while playing a recording that was made
on a known good deck - commercial tapes are usually (but not always) a
good choice.

Warning: once you adjust the azimith, any tapes previously recorded on
this transport may sound muddy.  If you only record and play your own
tapes on this deck, you may want to just leave it alone.

The azimith adjustment is usually a screw that pivots the record/playback
head.  It may be spring loaded and possibly fixed in place with a some
Loctite or varnish.  Often it will be accessible through a hole without
removing any covers but not always.  Look for it while in play or record
mode in back of any holes (which you had no idea had a purpose until now).
If there are no access holes, you will have to remove the loading door,
cover, or front panel.  Be sure you have the correct screw before turning
wildly - others may affect critical height or simply be mounting screws.

Play a tape with lots of good highs - classical instrumental music or jazz
are excellent.  Now, simply set the azimith adjustment for best sounding and
strongest high frequencies which should result in most natural sound.
Go slow - a 1/16 of a turn is significant.  Turn the screw back and forth
and leave it in the best sounding position.  Carefully put a dab of Loctite
or nail polish on the screw to prevent it from moving.

  4.10) Walkman/Discman power or sound intermittent

Note: for actual tape speed, operation, or sound quality issues, start with
the section: "General guide to tape deck cleaning and rubber parts replacement".

The socket that the AC adapter or headphones plug into is often quite
abused during normal operation.  This can lead to broken solder connections
where it joins the circuit board inside the unit. Test for this possibility
by wiggling the plug without moving or flexing the cable itself.  If the
sound cuts in and out or the tape player starts and stops or the radio
goes on and off, or the CD player resets or stops, then there is likely a
bad connection here.  Note: eliminate the alternate possibility that the
AC adapter or headphone cable is bad by wiggling and tugging on the cable
while holding the plug steady.  Further verify that it is not simply a
matter of dirt or grime interfering with a good connection.

The connections can be easily resoldered but you will need to open up the
case using.  Hopefully this will only require jeweler's screwdrivers and
great care.  (However, some Walkmen are constructed such that access to
the interior is virtually impossible without a hand-grenade.)  To repair
the connections, use a low wattage iron and fine rosin core solder.  Make
sure you do not introduce any solder bridges.  Try not to lose any of the

  4.11) Cassette or tape playback - one channel dead

This could be a bad playback head, bad connections, or a bad component
in the playback electronics.

First, confirm that the problem is not in your headphones, patch cables,
or the remainder of your audio system - try an alternate audio source
where possible.

To determine if the playback circuitry is working, gain access to the
terminals on the playback head  - a metal cased little cube near the
center of the tape side of the cassette.  There should be four wires coming
from it.  While the machine is supposed to be playing, touch the end of
a jeweler's screwdriver gently to each of the four terminals in turn.  When you
touch the good channel, you should hear a buzz from the appropriate speaker.
If you touch one terminal and get a buzz from the 'dead' channel, then
it is possible that the head is bad for that channel.  If you can touch
two different terminals and get a buzz in the bad channel for both, the
it is likely that the ground connection to the input preamp has fallen off.
If you do not get anything from the bad channel, then there is likely an
electronic problem in that channel.  Bad connections aside, the most common
problem area would be the audio amplifier - bad IC or capacitor.

  4.12) Distorted or erratic recording

First determine if it is a record or playback problem - play a tape
recorded on another machine or a commercial prerecorded tape.
Try a tape from this machine on another known working tape player.

If record is the problem and it has very distorted sound, this may be
a sign of a bad bias oscillator or switching circuit or record switch.
The bias is an ultrasonic signal that is impressed on the tape along
with the input signal.  Without it, the sound will be highly distorted.
In effect, it is a linearizing signal.

Check that the record select switch is clean - it may have many contacts
and may have collected a lot of crud.  If behavior changes with each
activation of the record switch, get some contact or tuner cleaner spray
and use the extension tube to spray inside the switch (with the power
off), put the switch through its paces several times and allow to dry
before powering it up.

If it is a portable subject to abuse, check for bad connections as well,
especially if, say, one channel comes and goes.

Beyond this, you can try to measure the signal going to the record heads
while in record mode.  You should be able to see a high frequency signal
in addition to the input signal.  If the either of these is absent, then
you need to trace back to its source and at this point will probably need
a schematic.

  4.13) Previous recording not erased

In this case both the original and new audio appear on the tape.  The most
likely cause (assuming your deck doesn't have some fancy sound-with-sound
or sound-on-sound modes that may be engaged) is a faulty erase head or its
driving signal.

The erase head precedes the record head and probably uses the same high
frequency signal as that for record bias to totally wipe the previous
recording.  (However, on really really cheap tape recorders, erase may just be
performed by a permanent magnet.)  If the new recordings are really distorted,
the bias oscillator itself may not be working.  The erase head is either part
of the REC/PLAY head assembly or a totally separate head.  Check for broken
wires to this head as well.  If you have an oscilloscope, monitor the signal
during record.  The erase head could also be defective or really dirty.

  4.14) Cassette player erratic autoreverse

Some of the autoreverse decks use a rotating magnet under or part of the
each reel and a reed switch or hall effect device to detect lack of motion
and do the autoreverse thing.

I had one from a Toyota where the plastic drive gear which included the
magnet and was part of the reel split and was getting stuck at the broken
tooth causing a reverse and eventually eating the tape.  It was $9 for
that little plastic gear.

Others are entirely mechanical and if there is a lack of lubrication,
dirt, tired belts or idlers, or broken parts they may start acting erratically.

Although there could be an electronic fault, carefully examine the mechanism
for obvious or subtle problems before breaking out the 'scope.

The following methods are use for autoreverse:

1. Optical sensor detecting the clear leader on the cassette.  Better tape
   decks use this for sensing at the end so that the reverse occurs just
   quickly at the end of the tape rather than waiting for the leader to go
   by and a second or two for the tape to stop.

2. Totally mechanical where a lever arm presses against the tape and when the
   tension increases with the reel stopped, it trips a mechanism to reverse.

3. Optical sensors on reel rotation.

4. Magnetic sensors on reel rotation - either hall effect devices or
   simple reed switches.

If the transport will run without a tape in place, see if the takeup reel
is rotating properly and whether the reverse still occurs.  If reel rotation
is normal but it still reverses, the either you have the optical tape
end sensor or there is some fault in the sensors for the reel rotation.
If the takeup reel does not rotate, then as suggested above, check for
bad belts or idler tire.

Belts and idler tires are readily available from places like MCM Electronics.

  4.15) Autoreverse audio not correct for either or both directions

This may mean that one or both directions is weak or erratic or that both
sets of tracks are playing simultaneously (one in reverse).

There are three common ways of implementing autoreverse with respect to
the tape heads:

1. Locate both the record/play heads and erase head on an assembly that can
   rotate (flip) 180 degrees depending on the direction.  Mechanical stops
   determine the precise position.

2. Locate both the record/play heads and erase head on an assembly that
   can shift transversely across the tape by one track distance depending
   on direction.  The connections to the L and R channels must be interchanged
   electronically in this case for one of the directions.

3. Provide a complete set of heads for both directions.  Selection is then
   done electronically or via a set of switch contacts controlled by the
   direction reversing mechanism.  (This would require duplicating 6 heads
   for a full record/play deck so it is more likely with a simple player which
   would then only require a total of 4 heads.)

Problems may be mechanical or electronic.  However, it is probably not what you
would consider head alignment.

In either design, the mechanism could be gummed up and not being properly
positioned in one or both directions.  There could be broken cables or
bad connections since (particularly with (1) and (2)) there could be
significant cable movement.

Check, clean, and lubricate the mechanics first before considering electronic
faults.  However, since all of these must select channels based on direction,
electronic or switching problems are quite possible.

  4.16) Walkman plays both sides of tape at once

One set of tracks will be playing backwards which may make for interesting
conversation!  There are two possibilities:

* Where a single pair of heads is used, the head assembly is misaligned
  and straddling both sets of tracks.  This would be the case with a
  non-autoreverse player or with an autoreverse player that shifts head
  position when it reverses direction.

  This is a mechanical problem with head alignment (height) or the shifting
  mechanism (autoreverse).

* For an autoreverse unit where the heads do not shift position (there are
  four heads gaps - one for each track but only 2 get selected for each
  direction), the head selection circuitry or switch is routing both sets of
  head signals to the amp.

  This is an electronic or switch contact problem.

  4.17) General tape speed problems - slow, fast, or dead

Are the speed problems sudden or gradual?  Over what period of time? Seconds,
minutes?  For portable devices, are you using a good set of their recommended
type of batteries?

Did this problem start suddenly or was this a tape recorder you found buried
under an inch thick layer of dust in an attic?

If the latter, then there could very well be multiple mechanical problems
due to deteriorated rubber parts - replace then or toss it.

Fast play could be an indication of a hard deteriorated pinch roller.
Or, you could have forgotten to turn off a 'fast dub' or 'quick copy' switch!

Clean and lubricate the mechanism.   Check for dry or tight bearings.

Is there any pattern to the problems - like with respect to the start
and end of cassettes?

If the tape speed has suddenly become excessive:

1. Mechanical.  If you had a recent tape eating episode, there may be
   a wad of tape wrapped around the capstan.  Remove it.  Alternatively,
   the pinch roller may not be fully engaging against the capstan
   and the takeup reel is simply pulling the tape through without any speed
   control.  Clean the mechanism, check for tired belts and springs.

2. Electrical.  The motor speed control is not working.  This may be either
   a mechanical governor inside the motor or a voltage regulator or other
   electronic control often also inside the motor.  In the latter case,
   you may be able to disassemble the motor and repair it.
   One possibility is that the series regulator has decided to turn into
   a short circuit.  This may be external or internal to the motor.

3. Cockpit error.  Some tape recorders and tape decks have various features
   (which you no doubt never use) that may have been inadvertently turned on
   or twiddled (perhaps by your 3 year old).  These include high speed dub as
   well as selectable and/or adjustable record or playback speed.

Slight tape speed error may simply mean that an internal adjustment is needed.
There may be an access hole on the motor or an external pot.  However, keep in
mind that any tapes you recorded on this machine (assuming it can record)
recently will play at an incorrect speed once you adjust the speed.

Is it slow and steady - no more wow and flutter than normal? Or slow and
erratic indicating that (1) the speed regulator is faulty, (2) some
bearings may need oil, (3) the pinch roller is glazed.

If the mechanics seem ok, then check for electronic problems with the
motor or regulator.  Sometimes there is a trimpot for speed adjustment
inside or external to the motor.  A faulty regulator or even a bad
connection may be the cause.

A variety of techniques are used to regulate the record/playback speed:

1. Mechanical governor inside motor - centrifugal contacts open at correct
   speed reducing current to motor.  If speed is too low, than springs could
   have weakened or contacts could be bad - open.  If speed is too high,
   contacts may be welded closed.  There may be a resistor and/or capacitor
   across the contacts.  An open resistor could conceivably cause unstable
   speed fluctuations.  A capacitor may be present to reduce electrical noise.

2. Voltage regulator inside motor case or external to motor.  The regulator
   or transistor may be faulty.  If power for the motor seems to come directly 
   from an unregulated supply, check across the motor terminals with an
   ohmmeter.  A low reading which is identical in both directions would 
   indicate a direct connection to the motor brushes with no internal
   regulator.  A high reading or one that is different in each direction
   indicates an internal electronic regulator - or you could just use your
   eyeballs to determine if there are any electronics inside the motor.  These
   can be disassembled and bad parts replaced.  There may be an access hole
   on the motor for an adjustment.  Alternatively, you could remove the guts
   and install an external regulator using an LM317 or similar part.

3. Active regulator with tachometer feedback from motor winding - there would
   be 4 wires instead of two coming out of the motor - 2 for power and 2 for
   tach.  Control circuitry could be bad or the tach output could be dead
   (speed too high).

4. If an optical strobe disk is located on the motor shaft, then it may be
   part of a speed control circuit. If it is on one of the reels - probably the
   takeup reel - then it simply operates the (electronic) tape counter or
   signals the controller that the takeup reel is turning - to catch tape

  4.18) Tape speed problems on older equipment

Older reel-to-reel decks (maybe even some cassette decks) likely use an AC
induction or synchronous motor driven from the power line.  Speed selection
is usually done by switching in different sets of motor windings and the use
of slip-on capstan/pinch roller sleeves.

Speed problems are most likely a result of

* Decayed rubber parts - belts, idler tires, pinch roller.
* Gummed up lubrication or worn bearings.
* Dried up or otherwise faulty capacitors in the motor circuitry.
* Faulty switches or wiring in associated with speed selection.
* An actual bad motor is possible but not that common.

See the appropriate sections in the chapters: "Turntables" and "Motors and Relays" for specific information on these types of problems.

  4.19) Tape speed adjustment made easy

OK, you have found the magic screw, but how to set the speed accurately?
Sometimes, there will be strobe disks on tape decks which will appear
stationary under fluorescent lighting (magnetic ballasts only - electronic
ballasts are usually high frequency and do not modulate the light intensity at
the power line frequency) but not usually.  So, you do it by ear:

Make a recording of a single tone on a tape recorder you trust - one
with accurate speed.

Suitable sources include:  a signal generator, electronic instrument,
Touch-Tone phone tone, PC sound card output or PC speaker, etc.  A frequency 
around 400-1000 Hz should work well.

Then, adjust the speed while listening to this same source simultaneously
with the tape being played back on the unit to be adjusted.  As you adjust
the speed, you will hear the pitch change.  As it approaches the correct
setting, you will hear the tones beat against each other.  When you are set
correctly, the pitches will be equal and the beat frequency will go to zero.
Even if you are tone deaf, you will easily be able to adjust pitch accuracy
to better than 1/10 of a semitone using this method.

Recording the 60 or 50 Hz power line (through a suitable isolated attenuator) 
and using this as a test tone will work if you have an oscilloscope.  Trigger
on 'line' and adjust playback speed to stop the trace from drifting.  However,
this is too low a frequency to be used accurately with your Mark I ears!

Some alternatives:

(From: Helling Bernie (helling@uwindsor.ca)).

A while ago I hit upon a way to set the speed on old cassette decks that
have gone out of speed. 

Use an electronic guitar tuner

They cost about $40, can be borrowed, etc...  Find a pro cassette deck that
is in speed, (the local campus radio station had a nice one)  and record a
tape full of A tone. My guitar tuner puts out tones too, so that was easy....

Play the tape in the suspect deck, while adjusting the motor trim to
replay a A tone perfectly on the tuner meter...


I never did have the patience to learn to play the guitar, so I got some use
off the tuning meter....

(From: Paul Temple" (mri@earthlink.net)).

Get a song on CD and a tape of the same album.  Play both at the same time
and adjust away!

  4.20) Sudden increase in flutter on tape decks or Walkmen

If your prized Walkman suddenly develops a severe case of warbling
sound check:

1. Batteries (where appropriate).  Almost dead batteries will greatly
   increase flutter.  Use of Nickel-Cadmium rechargeable batteries in
   place of alkalines may result in problems due to their lower voltage
   (1.2 V vs, 1.5 V per cell).

2. Tired belts - loose flabby deteriorated belts will produce varying,
   probably slow, speed as well.

3. Dirt or goo on pulleys.  Sometimes a glob of stuff gets stuck to a
   pulley and produces a periodic variation in speed.  I picked one up
   at a garage sale that had this problem.  I thought it was a bad motor
   until a careful examination revealed that the belt was jumping a mm
   or so on each rotation of an idler pulley.

4. Lack of lubrication - a dry or worn bearing may result in a variety
   of speed problems.

5. Bad speed regulator - either mechanical or electronic including
   bad solder connections or cracks in circuit board traces.

6. Bad power supply.

7. Bad tape.  Don't overlook this obvious possibility, try another one.

  4.21) Annoying tick every 30 seconds or so from audio output

This may be an almost inaudible tick, click, or pop which occurs fairly
regularly.  Its frequency may be dependent on many factors including
temperature, humidity, even whether you are at the start or end of a
cassette!  I may occur even if no cassette is present but the motors
are running.

The tick is probably due to a static discharge though other causes are
possible including mechanical problems and bad capacitors in the power

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

The problem is with a plastic or nylon gear, in contact with a
rubber belt or tire, generating a charge and discharging to some
nearby metal.  (It acts just like a miniature Van De Graff
generator --- sam.)

You have to listen around for it.  Murphy sez it will probably be
buried deep in the "guts" of the machine ;^)

I found it by touching a small wire to each of the pulleys until
it stopped "snapping" (actually, I got a little "snap" when I found it).

My "cure" was to use some stranded wire to create a "brush" that lightly
brushed against the pulley to bleed off the charge to the chassis.

I would first check the two big capstan flywheels and anything
powered by the main motor belt.  Look for any plastic, or metal
with plastic bushings and parts in contact with belts or tires.

(From: Ylo Mets (ylo@mango.mef.ki.se)).

I have experienced similar ticking in an old two-motor deck. There was some
dust collected between the takeup/wind motor shaft end and the metal chassis,
which evidently generated static electricity. Cleaning the dust did the trick,
although at first I thought the shaft was too close to the metal chassis. You
can check for the static by breathing slowly into the mechanism. The damp air
should discharge the static and the frequency of ticks decreases. Such ticking
is especially annoying because it is not exactly regular.

  4.22) Reel-to-reel tape deck problems

"I have a Teac 2300S reel to reel. 7" reel capacity, 1/4" tape. Two
 problems. First, right channel doesn't play back. Second, pinch roller
 doesn't come up to the capstan unless it's gently pushed."

(From: Davetech (dnesbitt@mindspring.com)).

I've repaired a few reel-to-reels in the past and generally find that they
all need three main things done:

* They need all the rubber parts - belts, tires, rollers - replaced.  Also the
  brake pads.

* They need all the controls and switches cleaned with a de-oxy type cleaner.
  (This may be the cause of your right channel problem).

* They need all the mechanical pivot points cleaned and re-lubed.  (This may
  be the problem with your pinch roller).

The last one I did, the old grease had hardened up so much that the heads
would not come up to contact the tape - and the grease was so hardened that
I could not get the linkage pulled off even using pliers and pulling as hard
as I could. I had to heat the post with a propane torch before the old grease
would soften enough that I could separate the parts.

I put enough time in the last unit that I could have fixed 3 or 4 VCR's, so
I'm not real big on taking them in.  They are generally very time consuming
to disassemble and reassemble and overhaul. But not usually technically
difficult to fix.

  4.23) Tape creeps off capstan

"I have a Sony reel-to-reel tape recorder.  When I play a tape, after a few
 seconds or minutes of playback, I can watch the tape creeping up the capstan
 between the rubber roller until it comes out the top and off the capstan."

The first thing to check - as with a VCR with similar symptoms - is the
condition of the rubber parts, in particular, the pinch roller.  Next, would
be tape path alignment and wear:

(From: Jack Schidt (dbutler@airmail.net)).

Check the reel height as well.  Capstans are upset if the reel tables have
shifted.  Use a straight edge between the two reel tables.  There are set
screws that sometimes get loose on some of these machines.

Check for a worn capstan bushing.  Disconnect the drive belt (if any) and see
it there is lateral play in the capstan.  If so, perhaps you can shim it
(either the motor [if equipped] or the idler).

Also make sure the tension is simply not too high.  You should be unable to
pull the tape through, but ridiculous force (as in something is BENT) will
cause this problem as well.

  4.24) 8-track player problems

These compete with turntables for classification in the Jurassic era.  8-track
equipment uses a cartridge with a single reel and enless loop tape (tape is
pulled from the center and returned to the outside).  The tape can only move
in the forward direction - rewind is not possible.

There were also similar competing but incompatible 4-track systems as well
as quadraphonic 8-track (when quad was all the rage).

Four pairs of channels allow for many hours of stereo playback without
changing cartridges.  A pair of playback heads is mechanically shifted
among the 4 possible sets of tracks when a metallic strip on the tape passes
over a set of contacts which operate a solenoid.

Most common problems are - you guessed it - mechanical with the cartridge or
in the drive or head shifting mechanism.  General comments with respect to
cassette decks apply here as well.

If you are really interested in resurrecting that 8-track player found under
the steamer trunk in your aunt's attic, there are many links to information on
8-track equipment, books, history, dealers, collecting, and everything else
8-track related that most people probably don't care much about anymore at the
following web site:

    * http://www.bway.net/~abbot/8track/resource.html.

There may be links for specific 8-track player repair information but I could
not locate them at this site.

However, this one seems to be the place to go for step-by-step 8-track
cartridge repair:

    * http://www.geocities.com/Paris/4831/       (Jeremy Larsen's Web Page)

  4.25) Repairing a cassette tape

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

This will be either easy or very hard. Question: do both of these have SCREWS
holding the tape together? If yes, EASY, if not, very HARD!

See what I'm getting at? Go to the store and get a quality tape that ALSO has
screws holding it together... you will transplant the insides into the new
cases. Take off the screws from both (old and new tape, do it one tape at a
time). Remove both top covers - make sure you don't lose the thin plastic
"lubricant" sheet (if any). Swap the tape reels - BE VERY SURE the old one
doesn't go flying off or it's more or less toast. Put the old tape reels into
the new case, make sure the tape follows the same path as the one you took out
did - so it doesn't get trapped by the case when you replace the top.  Put the
"lubricant" sheet back on top of the two reels of old tape and replace the
top. Put in all 5 screws. There you go. I'd say that this is 100% successful
every time I've tried it.

If your tapes don't use screws but are, rather, glued together, you're on your
own. I suggest a VERY sharp utility knife but tape damage is, alas, a very
REAL possibility.

Another way you can do this if you want to also replace the REELs (or if it's
a sealed unit) is to rewind the old tape, cut the tape LEADER and attach it to
the new cassette that you have already gutted. Put the new tape together (2
screws will do) and attach a small motor to the takeup reel. When the tape has
been transfereed to the new reel, cut it off the old one (the old cassette is
now empty) and open the new one again, attach the tape to the reel and put it
back together using all screws. Other than the leader being 2" shorter, you
have the old SOUL in a new BODY.

Of course, watch out that you wind the tape EXACTLY as it was and not on the
other side... etc. etc. I have done this twice. Grrrr.

It's a pain in the rear... so do it only if you have to...  I wouldn't do this
for money..... if that tells you anything.

Chapter 5) Turntables

  5.1) Turntable (record changer) maintenance

Here are general comments on oiling dinosaurs, oops sorry, turntables.

Usually there is a 'C-clip' or 'E-clip' which holds the platter (the thing
that rotates) onto the spindle.  It may be covered with a decorative
piece which can be easily removed.  The clip can be pryed off (gently)
with a small screwdriver (just don't lose it, though even this is not
a biggie so long as you never turn the thing up-side-down).

The platter can then be lifted straight up and off the spindle.  You will
see several things (this will vary depending on your particular unit):

1. A flat washer, sitting on a ball bearing race sitting on another flat
   washer (one or both of these washers may be missing.  Also, the top
   one may stick to the platter when it is removed.)  The ball bearings,
   shaft, washers, etc. should all be cleaned with degreaser and then
   lubed with a light grease.  If either the steel balls or the flat washers
   are corroded, replacement will be necessary or else there will be terrible
   audible rumble.  For now, it will at least work well enough to determine
   what else, if anything, needs attention.  Also clean and lubricate the
   platter bushing (center hole) and shaft (vertical post on which it rotates).

2. Changer gears etc.  These will have varying amounts of grease on them
   if it is not gummed up, leave them alone.  Put a drop or two of light
   oil on the shafts.  Inspect other linkages as well.   If the grease is
   gummed up on the gears or sliding linkages, you will need to clean it
   off thoroughly with degreaser and then use a small amount of high
   quality grease suitable for delicate mechanisms.  One cause of a changer
   failing to activate at the end of a record is gummed up grease.

3. Motor.  Check to see if the motor shaft turns freely and smoothly even
   if spun quickly between your fingers.  If it does - without squealing,
   don't do anything else.  If it is tight or makes noise, then you will need
   to carefully disassemble the motor and clean and lubricate the bearings at
   each end with light oil.  Don't lose any of the various washers/spacers that
   may be present on the shaft as it is removed from the end pieces and
   make sure to lubricate and return them to exactly the location and
   the same order they were in originally.

4. Clean the rubber parts with isopropyl alcohol and Q-tips or a lint free
   cloth until no more black stuff comes off and then dry thoroughly.  Now,
   inspect the belts (if any).  If belts are flabby or cracked or if they don't
   instantly return to their relaxed length if stretched 25% and released,
   they will need replacing.  Check the idler tire (if present).  If hard or
   cracked, it will need replacing as well.

Note: Light oil here means electric motor oil or even 3-In-One but NOT WD40.
Light grease means something that is suitable for fine mechanisms and is safe
for plastics.  Automotive bearing grease may not qualify.

  5.2) Speed control in turntables

Most inexpensive turntables/changers will use a synchronous motor or even
just an induction motor.  The only maintenance for the motor is cleaning
and lubrication.

Servo controlled turntables utilize a feedback technique which locks the
platter speed to a stable reference - either the power line (50/60 Hz) or
more commonly a crystal oscillator.  Here is one example:

A Sony turntable I repaired used a magnetic stripe pattern on the inside of the
platter which was sensed by a magnetic pickup.  The resulting signal was phase
locked to a stable reference and used to control a brushless DC direct
drive motor.  Speed would become erratic if (1) the magnetic pattern
were damaged, (2) the pickup position was moved too far from the surface
of the platter, (3) the Hall-effect sensors in the motor were bad, or
(4) the control electronics went bad.  In one case, it turned out that
one of the Hall effect sensors had failed in the motor.  This required
disassembling the motor and replacing the sensor - $4 from Sony.

  5.3) Turntable runs slow or fast after being moved

This is likely to be a mechanical problem - a belt that has worked loose and
is riding on the rim of the motor pulley or the wrong surface of the platter.

For an AC line driven motor (no electronics between the AC line and motor
except possible for a power transformer), it is virtually impossible for any
fault to result in a motor running faster than normal.  A motor may run slow
due to dirt, lubrication, or bearing problems.

Of course, check to see that any speed selector has not been accidentally
moved to the '16' or '78' position!

For a servo-locked turntable, a misalignment of the sensor used for speed
feedback could result in an incorrect - probably higher than normal (and
uncontrolled) speed.

  5.4) Wow, flutter, and rumble in a turntable

Wow and flutter refer to undesirable periodic variations in pitch caused by
changes in turntable (or tape deck) speed.  Wow would be a slow variation
(e.g., once per rotation) while flutter would be rapid (e.g., a motor
pulley with a bump).  Even if very slight, these faults will be all too
obvious with music but may go undetected at much higher levels for voice

Rumble is a very low frequency noise added to the audio caused by vibration
due to cheap, worn, dirty, or dry spindle bearings or by vibrations coupled
in from some other motor driven component or even from loudspeakers if the
volume is turned way up.  If really bad, rumble may sound like a freight train
in the next room.

For anyone only used to listening to CDs, even very small amounts of and of
these will prove very obvious and extremely objectionable.  Wow, flutter,
and rumble are undetectable - for all intents and purposes nonexistent -
with even the cheapest junkiest CD player.

For a common motor driven turntable, the following are likely causes:

1. Bad belt or idler.  Rubber 'rusts'.  If it is old, then almost certainly
   the rubber parts have deteriorated and will need replacement.
   Unfortunately, replacement parts are not as readily available as they
   once were.  The places listed at the end of this document may have some
   and there are many other sources but it is not as easy as one would like.

2. Dirty or worn spindle bearing.  This will cause rumble.  The thrust
   ball bearing can be cleaned and lubricated or replaced.   The platter
   bushing can be cleaned and lubricated.

3. Lump of crud stuck to motor pulley or idler, usually of unknown origin.

4. Dried up lubrication in motor, idler, or other rotating part.
   These can be cleaned and lubricated.

5. Bad motor (not that likely) except for lubrication in which case
   the motor can be disassembled, cleaned, and lubed.

6. Physical damage to platter - something heavy was dropped on it upsetting
   the delicate balance.

If you are attempting to restore a 20 year old turntable from Aunt Annie's
attic, don't even bother to power it up before replacing all the rubber parts
and cleaning and lubricating the motor, idler, and spindle bearing.

  5.5) Erratic sound from turntable

Sound that varies randomly in intensity or where one channel drops out
will usually be due to bad connections in the various units.  This could be:

1. At the pickup itself.  There may be small press fit connectors at the
   cartridge.  These sometimes become loose.  Gently remove each one
   (one at a time! so that you do not mix up the wiring) and squeeze with
   a pair of tweezers or needlenose pliers.  Snap in cartridges may have
   dirty contacts the springiness may have disappeared.

2. At the RCA plugs under the turntable which connect to the tonearm.
   Depending on your design and problem, you may need to simply clean
   with contact cleaner or squeeze the metal shell or center contact.

3. At the receiver, preamp, or amplifier.  Same as (2) above.

4. Sometimes the cables themselves will develop broken wires at one end
   or the other.  Easiest is to try a different set of cables.

  5.6) Turntable tracking and skating force adjustment

Tracking force keeps the stylus in the record's groove.  Too little is
as bad as too much.  It is best to follow the recommendations of the
cartridge/stylus manufacturer.  If you do not have this information, start
low and increase until you eliminate skipping or excessive distortion,
buzzing, or stuttering.  If too low, the stylus will make only partial contact
with the groove during high amplitude segments - it will jump from peak to
peak (or other portion) of the wave rather than smoothly and continuously
following it.  If too high, it will gouge the vinyl (or the shellac or
whatever depending on the vintage of your records) or in extreme cases,
bottom out on the cartridge's suspension.

Skating force compensation is applied to compensate for the fact that
except at one distance from the spindle (or with a linear drive tone
arm where this does not apply), the tone arm is not tangential
to the groove.  Imagine a perfectly flat record without any grooves.  If
you 'play' this, the tone arm will be stable at only one position somewhere
in the middle - where a line drawn through its pivot point and the stylus
is just tangential to a circle at that distance from the spindle.  The
skating is usually a simple spring which attempts to compensate for this
in such a way that the side force tending to move the stylus is minimized
at all positions.  Otherwise, the inner and outer walls of the groove
will experience a different force which will add distortion and affect
stereo separate and balance.

Skating force compensation is usually set based on the tracking force.

Note that if you are used to CDs or high quality cassettes, all the horrors
of records will be all to obvious unless you are using high-end equipment
(the kind that likely costs as much as your automobile) and meticulously
maintain your vinyl record collection.  Sonic defects like wow, flutter,
rumble, distortion, noise, imperfect stereo separation, skipping, and limited
frequency response are all facts of life for this technology which has not
changed in any fundamental way since Edison's time.

  5.7) Turntable tracking/skating problems

(From: Bill Turner (wrt@eskimo.com)).

You're bringing back memories.  I used to work for the leading Magnavox
warranty repair station in Los Angeles and I've repaired hundreds of the good
'ol Micromatics.  

Assuming there isn't something actually *pulling* the arm across the record
(in other words it's just sort of sliding across on it's own) the problem is
almost always the needle.  Either the tip is worn out, broken, missing, etc or
it could have just been dislodged from it's holder.  Lift up the arm and look
carefully at the needle.  The actual diamond tip is on the end of a short
shaft which in turn rests in a fork-shaped rubber holder.  This shaft is
easily knocked out of the holder, and if that's the case, just carefully put
it back.  

Hope this helps.  The Micromatic was a fine record player in it's time.  Good
luck, and let me know if I can help some other way.

  5.8) About stylus wear

So you still have one of those modified potters' wheels on which you place a
pre-formed piece of plastic that looks like a flattened dinner plate with a
hole in the middle and drag a needle over its surface to produce sound.  How
can you tell when the needle, err, stylus, has worn to the point (no pun...)
of requiring replacement?

It used to be that you could take it to any record store.  They would look at
the stylus under a microscope, and after a few choice utterances of "Oh my!"
followed by "This will strip the music right off your LPs", and would then
tell you that your stylus required replacement IMMEDIATELY whether it did or
not :-).  Of course, record stores don't exist anymore.

If you have a semi-decent microscope, you can do the same and get an honest
answer ;-). 100X should be more than sufficient, though getting the stylus
into position to view it may prove to be challenge.

The tip of a good stylus looks smooth and is spherical or ellipsoidal in
shape.  A worn stylus will exhibit edges/corners due to the wear of the tip.
Yes, even diamond will wear down if you drag it over thousands of miles of
vinyl.  Some of your LP record jackets may even have typical photos of good
and worn styli so check these out as well.

If the stylus is visibly worn:

1. The physical result will be that it will grind away at the grooves in your

2. The audible result of a bad needle will be excessive distortion and loss
   of high frequencies from (1).

After you replace it, your old records will still never sound as good as
they did before because of (1) :-(.

  5.9) Changer won't cycle automatically

If it is a basic old fully mechanical record changer, this is usually due
to gummed up grease.  There is a large gear which gets activated to operate
the lift-and-place mechanism.  Attached to this gear is a small swinging
segment that gets jogged by the tone arm reaching the proper position.  The
grease gets gummy and prevents this.  You have to remove the platter.

If it is a fancier changer with fully electronic controls, then it may be a
sensor or something in the circuitry.

Of course, there was this one I recently worked on where some previous repair
person (I am using this term generously) had glued the moving parts of the
changer mechanism together so it could not possibly ever have worked again
(until I unglued them all).

Chapter 6) Loudspeakers

  6.1) Loudspeaker anatomy

In this document, we use the terms 'loudspeaker' or 'speaker system' to
denote a unit consisting of one or more drivers in an acoustic enclosure
perhaps along with a frequency selective crossover, tone controls and
switches, fuses or circuit breakers.  Connections to the amplifier or
receiver are via terminals on the rear.  The front is covered with an
(optically) opaque or semitransparent grille which provides protection
and improves the appearance (depending on your point of view).

A 'driver' is the actual unit that converts electrical energy into sound
energy.  Most drivers use voice coil technology: a very low mass coil wound
on a light rigid tube is suspended within a powerful magnetic field
and attached to a paper, plastic, or composite cone.  The audio signal
causes the coil to move back and forth and this motion causes the cone
to move which causes the air to move which we perceive as sound.

The typical driver consists of several parts:

* Frame - a rigid steel or composite structure on which the driver is
  constructed.  The frame holds the magnet and core, cone suspension, and
  connection terminals.

* Magnet - this includes a powerful (usually ceramic, AlNiCo, or rare earth)
  magnet including a core structure provide a very narrow cylindrical air gap.
  This accounts for most of the mass of a driver.

* Voice coil - a one or two layer coil of fine wire wound on a light rigid
  cardboard, plastic, or composite tube suspended within the air gap of the
  magnet and connected via flexible wires to the electrical terminals.

* Cone - a roughly cone shaped very light and rigid structure that does
  the actual work of moving air molecules.  The cone in a woofer may be
  12 or more inches across.  The cone in a tweeter may only be an inch
  in diameter.  This is the part of the driver you actually see from the
  front of the speaker system with the grille removed.  The center is
  usually protected with a small plastic dome.

* Suspension - a corrugated flexible mounting for the voice coil called
  a 'spider' and outer ring of very soft plastic or foam.  Together, these
  allow the voice coil/cone combination to move readily in and out as a unit
  without tilting or or rubbing.  For most designs, there is a certain
  amount of springiness to this suspension.  Acoustic suspension loudspeaker,
  however, use the trapped air in a totally sealed speaker enclosure to
  provide the restoring force.

Inexpensive 'LoFi' devices like portable and clock radios, many TVs,
intercoms, and so forth use a single, cheap driver.  Some have a coaxial
pair of cones but this does little to improve the frequency response.

HiFi speakers systems will divide the audio frequency spectrum into several
bands and use drivers optimized for each.  The reason is that it is not
possible to design a single driver that has a uniform response for the
entire audio frequency spectrum.  A 'woofer' is large and massive and
handles the low base notes.  A 'tweeter' has a very low mass structure and
is used for the high frequencies.  A 'mid-range' handles the mid frequencies.
There may also be 'sub-woofers' for the very very low notes that we feel
more than hear.  Some systems may include 'super-tweeters' for the very highest
frequencies (which few people can hear.  This may make for some impressive
specifications but perhaps little else.)

A 'crossover' network - a set of inductors and capacitors - implements a
set of filters to direct the electrical signal (mostly) to the proper drivers.

Various controls or switches may be provided to allow for the adjustment
of low, mid, and high frequency response to match the room acoustics more
faithfully or to taste.  Fuses or circuit breakers may be included to
protect the speaker system from intentional (high volume levels) or
accidental (amplifier output stage blows) abuse.

  6.2) Loudspeaker problems

If you have a high quality and expensive set of loudspeaker, then
the cost of professional repair may be justified.  However, if the
problem is with speaker systems you might not write home about, then
read on.

Playing your music system at very high volume levels, especially CDs
which may have peaks that way exceed the ratings of your loudspeakers
is asking for trouble - but you knew that!  CDs can be deceiving because
the noise floor is so low that you are tempted to turn up the volume.
A peak comes along and your speaker cones are clear across the county
(remember the movie 'Back to the Future'?).  Loudspeaker systems are
generally pretty robust but continuous abuse can take its toll.

Problems with loudspeakers:

1. An entire speaker system is dead.

   Verify that the connections both at the speaker system and at the source
   are secure.  Check circuit breakers or fuses in the speaker system.  Reset
   or replace as needed.
   Make sure it is not the amplifier or other source that is defective
   by swapping channels if that is possible.  Alternatively, test for
   output using a speaker from another system or even a set of headphones
   (but keep the volume turned way down).  Assuming that these tests
   confirm that the speaker system is indeed not responding, you will
   need to get inside.

   It would take quite a blast of power to kill an entire speaker system.
   Therefore, it is likely that there is a simple bad connection inside,
   perhaps right at the terminal block.  You should be able to easily 
   trace the circuitry - this is not a missile guidance system after all -
   to locate the bad connection.  If nothing is found, then proceed to
   test the individual drivers as outlined below.
2. One or more drivers (the name for the individual speakers in a
   loudspeaker enclosure) is dead - no sound at all even when you
   place you ear right up to it.  The cause may be a bad driver,
   a bad component or bad connection in the crossover network.  Test
   these components as outlined below.

3. One or more drivers produces distorted or weak sound.  Distorted
   may mean fuzzy, buzzing, or scratchy a various volume levels.
   Most likely this is due to a bad driver but it could also be a
   defective component in the crossover - a capacitor for example
   or even a marginal connection.

Getting inside a speaker system usually means removing the decorative
grille if it snaps off or unscrewing the backpanel and/or terminal block.
Use your judgement.  With the grille removed, you will be able to unscrew
the individual drivers one at a time.  With the back off, you will have
access to all the internal components.  If sealing putty is used, don't
lose it or expect to obtain some replacement putty (non-hardening
window caulking like Mortite is suitable).

Test the components in the crossover network with a multimeter.  These
are simple parts like capacitors, inductors, and potentiometers or reostats.
Confirm that any circuit breakers or fuse holders have continuity.

Test the drivers on the low ohms scale of your multimeter.  Disconnect
one wire so that the crossover components will not influence the reading.
Woofers and midrange drivers should measure a few ohms.  If their
impedance is marked, the reading you get will probably be somewhat
lower but not 0.  If possible compare your readings with the same driver
in the good speaker system (if this is a stereo setup).  Some tweeters
(very small high frequency drivers) may have a series capacitor built
in which will result in an infinite ohms measurement.  Other than these,
a high reading indicates an open voice coil which means a bad driver.
In a comparison with an identical unit, a very low reading would mean
a partially or totally shorted voice coil, again meaning a bad driver.
Except for expensive systems with removable voice coil assemblies, either
of these usually mean that a replacement will be required for the entire
driver.  Sometimes an open voice coil can be repaired if the break can be

To confirm these tests, use an audio source to power just the suspect driver.
Your stereo system, a small amplifier attached to an audio source, or even a
pocket radio (use its speaker output if the headphone output does not have
enough power) will suffice.  The resulting sound will not be of high
quality because you do not have the enclosure sealed and it is only one
of the drivers in the system, but it should give you some idea of its
condition.  Again, comparing with an identical unit would be another

  6.3) Electrical causes for loudspeaker damage

These are not going to be covered by any warranty!  Of course, not mentioned
below are: fire, flood, falling from a tenth story window, getting run over
by a bulldozer, or being plugged into the wall outlet instead of the stereo,
etc. :-).

(Portions from: Lasse Langwadt Christensen (fuz@control.auc.dk)).

1. DC bias across speaker will cause the voice coil to overheat.  Windings may
   short out or open up.  Also see (3), below.  This usually results from an
   amplifier output stage failure - shorted capacitor, for example.

2. High power clipped signal:

   * A clipped signal contains a lot of high frequency energy and that could
     burn a tweeter, because the voice coil overheats.

   * The clipped signal could have a amplitude so large that the voice coil
     hits the magnet and is bent. It's a permanent damage but not always
     terminal, because the might still work, but make a scraping noise.  If
     you play loud with it for a long time (and it doesn't burn out - see (3),
     the part scraping against the magnet might wear off.

3. If the speaker is overheated, because of high power for a long period of
   time, the voice coil could expand and scrape against the magnet, and perhaps
   short some of the turns.  This is not always permanent, and some
   manufacturers use Teflon on the magnet, so that it's less likely to cause

  6.4) Repairing loudspeaker drivers

As noted above, if you are dealing with a high quality system, leave these
repairs to professionals or obtain an entire replacement as some reduction
in audio quality may result from the abuse you are about to inflict on
the poor defenseless driver.

We will address two types of repairs: physical damage to a speaker driver
cone and an open voice coil (actually, wiring outside the voice coil).
However, serious damage to the cone or just plain deterioration of the
suspension components may require replacement of the entire driver unless
a close enough match can be found.

For more information on loudspeaker repair, see: "Speakers (big, small, in
between)" also at this site.

  6.5) Repairing speaker driver cones

Minor damage to the cone can be repaired using a flexible adhesive like
weatherstrip cement and a piece of thick paper to reinforce the seam or
hole if necessary.  Since this will not totally perfect match with the
original paper cone, there could be audible distortion at certain
frequencies particularly at higher volume levels.  However, such a repair
will be better than nothing.  Cut the paper in a shape and size to just
overlap both sides of the torn area or completely cover the puncture.
Use just the smallest amount of adhesive to fasten your 'splint' to the
cone.  The less material you add, the more likely that the audio effects
will be minimal.

(From: M. Przytarski (m.r.p.@ix.netcom.com)).

I have repaired many field-coil speakers, and there is one sure proof
way my grandfather showed me (and several Tube Radio rebuilding mags
suggest the same).

Take a milk glue (Elmers or such), and rub it around the crack.  Then
take a piece of brown lunch bag and rub it with glue.  Place it over
the crack, and rub some glue on it, pressing it in place.  The glue
should by now soak the paper of the cone and bag.  When dried you cant
tell the difference in sound and its as sturdy as ever.  This also
works for those units that a animal (or kid) has put a hole in.  I
repaired a speaker that was missing almost half of the cone from mice.
It sounds great and was cheap to do.

  6.6) Some sources for loudspeaker repair parts and services

(I have not dealt with any of these places personally - these are all based
on recommendations of others.)

* Simply Speakers, 11203 49th St. N., Clearwater, FL 34622,  Voice phone:
  (813) 571-1245, Fax: (813) 571-4041, http://www.simply-speakers.com,
  provides speaker repair services and also sells do-it-yourself refoaming
  kits for repairing foam edge surrounds on most round 4" to 15" and oval
  6" x 9" speakers.

* Stepp Audio Technologies, P.O. Box 1088, Flat Rock, NC 28731, 1-704-697-9001.

* The Circuit Shop, 3716 28th Street, Kentwood, MI 49512, 1-800-593-0869 or

(From: Raymond Carlsen (rrcc@u.washington.edu)).

Various sizes of paper cones and foam-edge replacements are available from
MAT Electronics @ 1-800-628-1118.  They range in price from less than a dollar
to about $5 for the largest (15") drivers.  The downside is there is a $25
minimum.  However, they also sell electronic components like flybacks, video
heads and belts, ICs and transistors, etc.  So coming up with a minimum order
may not be too difficult.

(From: Johnion (johnion@aol.com)).

I was given a pair of infinity speakers and ordered replacement cones from The
Speaker Plac. As long as the problem is just the cones, the kit is great (and

These are the numbers I used around a 1-1/2 years ago:

* The Speaker Place - NEW FOAM, 3047 West Henrietta Road, Rochester, NY 14623,
  Phone: 1-800-NEWFOAM (1-800-639-3626), Fax: 1-800-2FXFOAM (1-800-239-3626),
  Voice Mail: 1-800-FOAMMAIL (1-800-362-6624). Email NEWFOAM@msn.com, Web:

(From: T Schwartz (toschwartz@worldnet.att.net)).

I've had excellent results sending drivers to Millersound Labs:

* Millersound Labs, 1422 Taylor Road, Lansdale, PA 19446, Phone 215-412-7700,
  Fax 215-412-0542

  They can re-foam or re-cone depending on what is needed, they are fast, easy
  to deal with, and IMHO, reasonably priced.  Call them for a quote.

(From: jl (jlager@tir.com)).

* Orange County Speaker, 12141 Mariners Way, Garden Grove, California,

* (From: Aan Jerig (ajerig@gate.net)).

  Lakes Loudspeaker, 4400 W. Hillsboro Blvd., Coconut Creek, FL 33073,

  6.7) Repairing an open driver

An open driver can sometimes be rescued by tracing the input wires through
the cone and under the center protective dome.  The most likely places
for these wires to break are right at the place where they pass through
the cone and just after they pass under the dome.  Note: some drivers have
replaceable voice coil units.  If this is the case, you should probably
just replace the entire unit.

First, scrape away the insulating varnish on the front of the cone where
the wires emerge and head toward the center.  Use your ohmmeter to test
for continuity here.  If you find that you now are measuring a reasonable
resistance - a few ohms, then trace back to determine which of the two
wires is broken or has had the solder connection come loose.  If it is still
infinite, you will have to go under the dome.

Use an Xacto knife to carefully remove the dome.  Use a shallow angle and
cut as near the edge as you can.  Take care not to puncture the paper cone
which may continue under the dome as the voice coil may be of a smaller
diameter than the dome.  The shallow cut will also provide a base to
reattach the dome if you are successful.  Carefully scrape off a bit
of the enamel insulation as near to the voice coil as possible and test
with your ohmmeter once again.  If the resistance is still infinite, there
is nothing more you can do but salvage the magnet for fun experiments or
erasing floppy disks.  There is essentially no way to replace just the
voice coil unless your driver has a removable voice coil unit (in which
case you would not be reading this).

If the resistance now measures normal - a few ohms, trace back to
determine which wire is broken and use some fine (e.g., #30 gauge) wire
to bridge the break.  You will have to scrape off the enamel insulation
to permit the solder to adhere.  Make sure it is secure mechanically first -
a speaker cone is a rather violent environment for soldered connections.
Finally, use some flexible adhesive to protect and reinforce the solder
connections, to glue down your new wire along its entire length, to
protect and reinforce the place where the wire passes through the cone,
and finally, to reattach the central dome.  Let the adhesive dry thoroughly
before playing the finale to the 1812 Overture.

  6.8) Loudspeakers - repair or replace?

Assuming that the cabinet is in reasonable condition, the question arises:
is it worth replacing broken, damaged, or worn out drivers or faulty crossover
components that are not repairable rather than just dumping the speaker

It is very straightforward to swap drivers as long as you get ones with
similar characteristics.  It all depends on what you want out of a loudspeaker.
If you are basically happy with them, then it will be a lot cheaper than
replacing the entire speaker system(s).  However, speaker system quality has
improved considerably in the last 15 years so now may be the time to upgrade.

As far as crossover components are concerned, these are basically common
electronic parts and replacement is probably worthwhile.

However, if one driver has a deteriorated suspension, it is likely that
its mate does as well and that other drivers may not far behind.  Replacing
**all** the internal components of a loudspeaker may not be worth it.

Radio Shack as well as places like MCM Electronics and Dalbani have
a variety of replacement drivers, and crossovers and parts.

  6.9) Speakers wired in series?

(From: Frank Fendley (frank.fendley@datacom.iglou.com)).

Wiring speakers in series increases the impedance of the load, generally 
allowing less expensive output chips and smaller heatsinks, due to reduced
current.  It also decreases the amount of output audio power in most cases,
since power is inversely proportional to impedance for a given voltage.

Many cheaper home stereo receiver and power amps are configured in a similar
manner.  If you have a switch and output connectors for "A" and "B" speakers, 
in some cases when you turn the switch to "A+B", the two left speakers and the
two right speakers are wired in series.   To find out if this is the case on
your stereo, hook up only one set of speakers to the "A" jacks.   Turn the
speaker select switch to "A+B".   If you have no audio through the speakers,
then your receiver or power amp is configured to place the speakers in series 
with both sets of speakers are connected.   On better stereo equipment, if you
have only one set of speakers and select the "A+B" switch setting, your 
speakers will still function, indicating that the speakers are wired in 
parallel in the "both" position.

Bottom line - the answer is money (isn't the answer always money?).   It's 
cheaper for the manufacturers to design for speakers in series.

  6.10) Comments on speaker shielding

When loudspeakers - even those little speakers that came with your PC - are
near TVs or monitors, there may be problems with the fringe fields of the
powerful magnets affecting color purity, convergence, or geometry.  Speakers
designed to be used with PCs in close proximity to their monitor will likely
include some internal shielding.  This may even be effective.  However, the
large powerful loudspeakers used with high performance stereo systems will
likely not have such shielding.  The best solution where display problems have
been traced to the loudspeakers is to move them further away from the TV or
monitor (and then degauss the CRT to remove the residual magnetism.  Where
this is not possible, shielding of the speakers may be possible:

(Also see the document: "TV and Monitor CRT (Picture Tube) Information".)

(From: Lionel Wagner (ck508@freenet.carleton.ca)).

Put a Tin can over the magnet.  This will reduce the external field by
about 50%.  If more shielding is desired, put additional cans over the
first, in layers, like Russian dolls.  (Note: a Tin can is actually made
nearly entirely of steel - the term 'Tin' is historical. --- sam)

(From: Nicholas Bodley (nbodley@tiac.net)).

While both electrostatic and electromagnetic (E/M) fields can affect the paths
of the electron beams in a CRT, only E/M fields are likely to be strong enough
to be a problem.

Magnetic shields have existed for about a century at least. Some decades ago,
a tradenamed alloy called Mu-Metal became famous, but it lost its effectiveness
when bent or otherwise stressed. Restoring it to usefulness required hydrogen
annealing, something rarely done in a home shop (maybe one or two in the USA). 

More-recent alloys are much less fussy; tradenames are Netic and Co-Netic.

Magnetic shields don't block lines of force; they have high permeability,
vastly more than air, and they guide the magnetism around what they are
shielding; they make it bypass the protected items.

I have been around some shielded speakers recently, but never saw any
disassembled. They looked conventional, must have had the "giant thick
washer" (my term) magnet, and seemed to have a larger front polepiece than

They had a shielding can around the magnet; there was a gap between the front
edge of the can and the polepiece. I suspect that a second internal magnet was
placed between the rear of the main magnet and the rear (bottom) of the can,
so there would be minimal flux at the gap between the can and the front
polepiece. Holding pieces of steel close to the gap between the can and the
polepiece showed very little flux there.

Modern magnets are not easy to demagnetize, in general.

(From: Dave Roberts (dave@aasl.demon.co.uk)).

The *good* so-called magnetically screened speakers rely on two means of
controlling stray flux.  The static field from the magnet on the speaker
(which would cause colour purity problems) is minimized by the design of the
magnet.  This is often at the expense of gap field linearity, leading to
greater distortion - not that most users seem to worry about that...

The mains varying field is minimized by use of a toroidal mains transformer,
but the more recent mains powered speakers seem to be coming with *plug top*
PSUs, which take the problem further away.

Chapter 7) Telephone Equipment

  7.1) Telephone basics

* Connections to 'Plain Old Telephone Service (POTS)' is via two wires.
  POTS is the type nearly everyone currently has to their residence.  Newer
  ISDN or fiber lines use different techniques.

* The wires are called 'Tip' and 'Ring'.  This terminology has nothing to do
  with telephone ringing but is historical; Tip and Ring were connected
  to the tip and ring respectively of the plug used on manual switchboards.

* Tip and Ring color codes are as follows - this is not always adhered to!

                              Type A               Type B
      Phone line             Tip,Ring             Tip,Ring
   First line (Pair 1)      Green,Red            White,Blue
   Second line (Pair 2)     Black,Yellow         White,Orange
   Third line (Pair 3)      White,Blue           White,Green

  Type A is often simply called 'quad' and is the most inexpensive cable.
  However, the conductors are usually not twisted and type A should not
  be employed in new installations especially where computer modems or fax
  machines are to be used on any of the lines as crosstalk between
  multiple phone circuits in the same cable may result in excessive
  transmission errors and interference with normal phone conversations.

  For type B, the colors refer to the dominant one if the wires are striped.
  Each pair is twisted together which greatly reduces crosstalk.

* On RJ11 type connectors, Pair 1 is the central two wires, Pair 2 is the
  next two, and Pair 3 are the outer wires if there are 6 conductors - many
  RJ11 cables only have 2 or 4.

* Tip will be approximately +50 VDC with respect to Ring when phones (or
  computer modems or fax machines) are on-hook.  Test with a multimeter.

* Ringing voltage is about 90 VAC.  A neon light bulb (NE2) can be used
  to test for this if a multimeter is not available.

* When off-hook (dialing or talking), there will be a DC voltage of
  approximately 5 to 15 V between Tip and Ring.  This is needed for the
  phone circuit and also is used to power the dialing in phones without
  a separate AC supply or adapter.

* The on-hook and ringing voltages can give you a shock but are probably
  not particularly dangerous to healthy people.  Still, it is best to
  work on phone wiring with it disconnected from the telephone company's
  feed or with another phone on the same circuit off-hook.

* Some phones will work with only one of the two possible polarities of
  Tip and Ring while others incorporate a bridge rectifier (for power)
  and will work either way - test both ways if a phone does not dial
  or work at all.

* DTMF refers to the Dual Tone Multi-Frequency dialing touch tone codes.
  Each number, *, and #, are represented by a pair of audio frequencies.
  (You can hear the individual ones by holding down multiple buttons on
  an old style ATT Touch Tone phone).  See the section: "DTMF codes".

  7.2) DTMF codes

DTMF (Dual Tone Multi-Frequency) are the tones that phones use.  The
frequencies are as follows:

     Hz     1209   1336  1477   1633
    697       1      2      3     A
    770       4      5      6     B
    852       7      8      9     C
    941       *      0      #     D

Follow the rows and columns to the number you want to know the frequencies
of and this  table will show you.  The column of letters at the right is on
some Ham radios.

Where an old style ATT Touch Tone phone's DTMF frequencies need to be adjusted,
accuracy of better than 1 Hz is easily obtained without fancy equipment - just
another working tone dialing phone.  See the section: "Classic ATT Touch Tone phone 'battlewagon' will not dial properly".

For more information on DTMF coding, decoding, equipment, chips, etc., see
the DTMF FAQ at:


  7.3) Phone jack or extension installation or repair

The phone companies would have you believe that installing or repairing
phone wiring is somewhere between rocket science and nuclear physics in
complexity.  In fact:

* Installing new jacks consists of two parts: running the wires and
  hooking them up.  The only difficulty with running the wires is getting
  between floors.  Connecting them is a matter of matching the colors
  of the insulation, stripping, wrapping around screws, and tightening
  the screws.  Even if you are color blind, this is not difficult.

* Unless you disturb it, phone wiring rarely goes bad - even in old
  houses.  Thus, if you have any amount of handyperson ability, paying
  the $2 a month inside wiring insurance is throwing away $24 a year.

* Unlike electrical wiring, phone wiring does not have serious safety
  issues associated with it.  However, you could get a mild shock from
  touching the two wires of an active phone line.  The on-hook voltage is
  about 50 VDC and if someone were to try calling your number at the same
  time, the ringing voltage is around 90 VAC.  Both of these are easily dealt
  with: put a jumper between the two phone wires where they enter your house
  while you are working on the wiring.  This will result in an 'off hook'
  condition and outside callers will get a busy signal.

  7.4) Answering machine comments

Most answering machines still use one or two tape decks.  Most problems
are mechanical.  Refer to the sections on the relevant tape player/recorder
problems.  The newest ones are fully digital electronic - forget repairs
unless obvious bad connections, physical damage, power supply, or phone
line side failure.

* Many non-mechanical problems with answering machines are related to the
  circuitry connected to the phone line.  This is subject to the high on-hook
  and ringing voltage and possible voltage spikes due to lightning, etc.

  Testing of the components on the phone line side of the coupling transformer
  is a worthwhile exercise and may reveal a shorted semiconductor or capacitor.

  See the section: "Checking phones and answering machines for electronic problems".

* If the outgoing message (OGM) or phone messages do not record or playback,
  check for broken wires at the appropriate tape heads and clean the mode
  selector switches.

* With endless loops outgoing message cassettes, the metal strip that is
  used to sense the beginning can wear or become dirty.  Try a new cassette
  or clean it.

* Like VCRs, there may be various 'mode switches' or position sensors.  Where
  these are physical switches, they may have dirty or worn contacts.  Optical
  sensors can fail as well though it is unusual.

* Mechanical problems unique to answering machine tape transports are also
  possible.  Some very clever engineering is often used to share parts
  where two tape transports are used. Parts may have popped off or broken.
  Springs may have sprung or weakened.  Sliding parts may have jammed.  Look
  for loose parts or broken pieces when the unit is disassembled.  Careful
  inspection during operation may reveal whether it is getting stuck due to a
  mechanical failure.

  7.5) Answering machine delays after playing OGM

This may be one of those machines where it has to go through the entire
outgoing message (OGM) tape before allowing recording of the phone
conversation - If it is, then just get yourself the shortest outgoing
message tape you can find and time your OGM to nearly fill it.

Also, if you are trying to use an OGM tape recorded on another answering
machine, even if the tape is compatible, the frequency or coding of the
control tones - the beeps - may not be the same.  Try re-recording it
on the machine in question.

If these are not the problems, the machine may not be sensing the beep code
put on the tape when you record the OGM or the beep is not being recorded
properly.  This is likely an electronic or logic problem requiring the
schematic unless you get lucky with bad connections or a broken wire at
the tape head.

  7.6) Answering machine picks up then hangs up

* If it has a 'telco' and a 'phone' connector verify that you are plugged
  into the 'telco'.  Otherwise, it may hang itself up.  Who knows.
  If someone else attempted a repair, these jacks could even have been
  replaced interchanged.

* Measure voltage on the relay coil.  If it actually disappears when
  the relay cuts out, then something is telling the relay to turn off.
  If it is just reduced, then there may be a power problem.  If it
  is relatively stable, then the relay may be bad.

* Test components near the telephone connection for shorts/opens.
  Parts connected to the telephone line get abused by the ringing
  voltage and other transients.  Maybe you will get lucky and find
  a fried part.

* If you can identify the power supply outputs, verify their voltages
  if possible.  Check the 'wall wart' if it uses one for proper output.

* Make sure that the tape mechanisms have completed their cycles.  While
  unlikely, it is possible that the logic gets confused if one of the
  tape units has not reset itself due to a mechanical fault like a bad belt.

* As usual with cheaply made consumer stuff (as well as cheaply
  made expensive industrial stuff), check for bad connections.

Beyond this, circuit diagrams would be a definite plus.

  7.7) Answering machine does not complete cycle

This is often a mechanical problem.  As it goes through the cycle, see
if the mechanism is perhaps getting hung up at a certain point do to
a weak spring or motor.  A cam may get stuck or a solenoid may fail
to engage.  Gently prodding the uncooperative part (or any likely parts
if the appropriate one is not obvious) may convince it to continue and
allow you to make a diagnosis.

For endless loop outgoing cassettes make sure that the metal sense strip
is not worn off and that the sensor is making good contact.  Try a new
outgoing message cassette or manually short the sensor contacts to see
if it will then shut down.

  7.8) Answering machine has weak outgoing message

You probably have no way of knowing since you probably never listen
to the outgoing message, but did the problem happen suddenly?

Does playback of the outgoing message directly to the speaker appear
to be at normal volume?

Do incoming messaged get recorded at normal volume?

First, confirm that the unit is in good mechanical condition.  See the
section: "General guide to tape deck cleaning and rubber parts replacement".
Clean the tape head and inspect for anything that may be interfering with
good tape-head contact.  Clean the internal record/play selector switches.
Dirty contacts can result in any number of symptoms.

Assuming that none of this helps significantly, you are left with a problem
in the electronics.

If local record and playback of the the outgoing message works normally, the
problem is not a bad tape head.  It is probably in the interface to the phone

If local record and/or playback do not work correctly, then there are likely
problems with that circuitry. 

One other slight possibility is that you have so much equipment (phones,
modems, fax machines, etc.) on the phone line that in your house that the
answering machine is not able to drive the line properly and reduced
outgoing message volume is the result.

  7.9) Newly installed phone will not tone dial

If a Touch Tone phone that was previously working now does not tone dial
from a new jack or new residence (the button presses are totally ignored,
but all other functions are unaffected), the red and green wires are
probably interchanged at the new jack, or the phone itself is miswired
(the wires inside the phone may have been interchanged to compensate for
an incorrectly wired jack at the old location).

Newer electronic phones will utilize either polarity.  The older ATT
battlewagons will only dial when hooked up with the correct polarity.
This does not affect conversation, ring, or rotary phones.

  7.10) Cordless phone problems

There are several types of problems with cordless phones that can be
diagnosed and repaired without sophisticated test equipment.  Anything
involving problems with the RF or digital circuitry is not likely to
be within the scope of your capabilities, at least not without complete
schematics (yeh, right), test equipment, and a miracle or two.

1. Bad rechargeable battery - dead, shorted cell(s), or reduced capacity.
   The NiCd battery packs in cordless phones are usually easily replaced
   for around $5-10.  This really is the best solution.  The problem is
   almost never in the charging circuits.  Replacing individual cells is
   not recommended.  Battery packs can be built up from individual NiCd
   cells with solder tabs for a modest cost savings.  Reuse the old battery 
   pack connector (you may need to do this with a replacement pack as well
   if the new connector is not identical to the old one), double check
   polarity, and tape and insulate your homemade pack after soldering to
   prevent shorts.

   A NiCd battery pack with shorted cells will either prevent operation
   totally or keep the 'battery low' light resulting in a weak, noisy, or
   intermittent connection.  If the voltage measured on the battery pack
   after 24 hours of charging is less than 1.2 V times the number of cells
   in the pack, it is most likely bad.

2. Dirty keypad - resulting in intermittent, incorrect, or no operation
   of buttons on handset.  This may be due to internal migration of some
   unidentified substance (how else to describe disgusting sticky gunk that
   has no right being there on multiple samples of the same model phone) or
   from external spills.  If you are lucky, the keypad can be disassembled
   without resorting to drastic measures.  There may be screws or it may
   snap apart once access is gained to the inside of the handset.  Clean
   contact surfaces on both the rubber button panel (or plastic keys) and
   the circuit board first with soap and water and then with isopropyl
   alcohol.  Dry thoroughly.

   If the keypad is assembled with 'upset' plastic (fancy term for little
   melted plastic posts), then you should probably try contact cleaner sprayed
   as best as possible through any openings before attempting to cut these
   away since reassembling the keypad without the plastic posts will be
   difficult.  However, I have successfully repaired these by breaking off the
   tops of the posts to remove the circuit board and rubber keys, and then
   using a dab of windshield sealer on each post as an adhesive to hold the
   thing together after cleaning.  However, I much prefer screws :-).

3. Bad AC adapter on base station - see the chapter: "AC Adapters."  This
   will likely result in a dead base station.

4. Bad phone line connection - don't ignore this possibility - test with
   another phone.

5. Bad circuitry on phone line side of interface (coupling transformer) -
   inspect for blown or shorted components.

6. Bad connections or broken circuit board - if the handset has seen
   violent service, these are likely possibilities.  See the section
   on: "Equipment dropped or abused".

7. You forgot the code number - some phones use a multidigit code number
   as a marginal security feature which must match on handset and base
   station.  If the battery goes dead in the handset or the AC adapter
   is pulled on the base station, this code may be forgotten.  You do have
   the user's manual, right?

   BTW, do set this code to a non-default value.  I was once able to dial out
   on my neighbor's cordless phone using my phone from my house as a result, I
   suspect, of their phone being set to its default code!

8. Base station and handset out of sync - some models require that the base
   station initialize the handset before any communication is possible
   between them.  Put the handset on the base station for a few seconds to
   reset.  This can happen at any time due to circumstances beyond human
   control but will almost certainly happen if you replace or disconnect the
   battery in the handset of these model phones.

  7.11) Cordless phone keypads

(From: Martin Sniedze (MSniedze@STRNNTS1.telecom.com.au)).

I found that the keypad was always getting wet/oily somehow.  Cleaning with
alcohol only fixed the dialing problem for about a week. A bit of asking at
phone repairer revealed that sanyo has a 'possible' problem with the keypads
absorbing/emitting the oily substance. The repairer sold me a membrane that
goes between the silicon keypad and the PCB, it has carbon pads on the back.
It stops the moisture getting through. It has completely fixed the problem in
my phone (it was done 6 months ago). They should be free.

  7.12) Erratic or noisy telephone equipment

The following applies to normal desk or wall phones, cordless phones, modems,
answering machines, fax machines - essentially anything plugged or wired into
the phone system.

Always check the cords first - especially the one between the handset
and the desk or wall phone itself since it gets a lot of abuse.  Noisy,
intermittent, or totally dead behavior is possible.  In some cases, even the
(electronics) ringer will not work if a wire in this cord is broken as the
ringing signal is generated in the handset and sent back to the ringer unit.
Try jiggling the cord at both ends to see if noise is generated or behavior
changes.  Even permanently wired in cords are replaceable - just take care
to draw a diagram and/or label all the wires before disconnecting the old one.

Bad connections are relatively rare in original ATT dial or Touch Tone
telephones.  These old phones also used very high quality contacts for the
on-hook, dial, and button switches which rarely resulted in problems.
However, with the multitude of modern equipment of all degrees of quality,
bad connections and dirty or degraded switches and relays are very common.

The various microswitches and/or relays for on-hook and other functions
seem to be particularly prone to degredation if not properly specified
in the design.  If phone line pickup or mode switching is noisy or erratic,
this is a likely cause.  Most of these swiches and relays are replaceable
although creativity may be required as an exact match may not be easy
to locate.

To assure that the problem is actually with the particular piece of equipment,
disconnect other devices on the same telephone line.  Aside from the obvious
oversight of a phone that has not been hung up, modems or fax machines that
are not powered on may load the phone lines excessively.  For example, if you
have two PCs with modem connections to the same phone line, the signal quality
on one of them may degrade to the point of reducing the effective transmission
speed, producing an excessive error rate, or not successfully connecting at
all if the other is turned off.  (They may also behave strangely if the
Originate/Answer settings of the modem are set incorrectly - but that is
another matter.)

  7.13) Checking phones and answering machines for electronic problems

Most signal problems will be related to failed components on the telephone
line side of the coupling transformer including components in the phone
line derived power supply (if used).  Phone lines are subject to all kinds
of abuse including lightning strikes (although something significant may
do extensive damage beyond reasonably hope of repair).

* Test all the components on the telephone line side of the coupling
  transformer when line connect, detect, or dial problems are encountered.
  There may be shorted semiconductors due to a voltage spike or just bad luck.

* Some units extract power from the phone line and the rectifiers or other
  related components can go bad.  This can result in either power problems
  (telephone is totally dead) or dialing problems.

* Make sure you are using the proper AC adapter and test it for correct output.

* There could be a defective power supply inside the phone - the regulator
  could be shorted or a filter capacitor could be dried up.  See the chapter:
  "Equipment Power Supplies".

* Check for loose or broken connections - phones get dropped.

* For erratic dialing problems, inspect and clean the keypad and other
  switch contacts.  Also see the section: "Cordless phone problems".

  7.14) Modem problems

First, confirm that your modem settings are correct - reset the modem
to factory defaults using the Hayes AT commands (e.g., AT&F1) or
dip switch settings.  Confirm that your software is set up correctly and
that there are no IRQ or IO address conflicts.

If the modem starts to dial but aborts and hangs up, confirm that you
do not have the wiring of the 'telco' and 'phone' connectors interchanges.

Also see the section: "Erratic or noisy telephone equipment".

Since the phone line is subject to all kinds of abuse, most actual problems
(that are not software related), will be on the phone line side of the
coupling transformer.

* There will be various diodes, transistors, capacitors, opto-isolators, and
  relays for routing the incoming and outgoing signals, or for protection and
  these can fail shorted or open.

* There may be an actual fuse (or more than one) as well - but it will
  probably not look like a common fuse but may be very tiny - more like a
  resistor - or even a surface mount part.  Hopefully, the circuit board will
  be marked 'F1' or 'PR1' or something similar.  Check fuses for opens.

* A lightning strike is likely to obliterate components in the modem beyond
  even your abilities to salvage it.  If it arcs over the coupling transformer
  or just induces a large enough voltage spike, the logic circuitry will be
  history.  However, in many cases, damage is minor.

If you have signal problems - a modem will try to dial out but not
make its way to the phone line, testing on each side of the couping
transformer with a scope or Hi-Z headphones should be able to determine
if the problem is on the logic or phone line side of the device.

Check that the proper AC adapter is being used (if relevant) and that is
is putting out the proper voltage.  Check the internal power supply components
for proper output.  They are often common IC regulators like the 7805 and
are easily tested.  Replacements are inexpensive and plentiful.

(From: Rick Miller (wizkid@mv.mv.com)).

First thing to check: almost all modems have a pair of low-value
resistors (10-20 ohm) between the phone line and their line transformer.

I got a 2400 baud voicemail modem for free this way!  Repaired an
"unrepairable" modem (according to the ACER computer technician! :) )

Replaced a "booger resister" with a real 1/2 job.... had to work hard to
get the leads soldered onto the SMT pads!:)

(From: Jordan Hazen (jnh@aardvark.cen.ufl.edu)).

Yes, in my experience you're much more likely to sustain damage from a
phone-line surge than anything on the power grid.  Modem electronics tend
to be more delicate than the stuff in your power supply.

First thing to check: almost all modems have a pair of low-value
resistors (10-20 ohm) between the phone line and their line transformer.
These are intended to take the brunt of a lightning hit and protect
the electronics upstream.  Traditionally, these have been large,
high-current resistors (like 1/2 watt), but sometimes now they try
to get away with little 1/16-watt surface mount ones that are much more
likely to blow.  Sometimes it's obvious when the resistors have died,
with visible singe marks, pieces blown away(!), etc.  Usually these
fail as an open, resulting in "NO DIALTONE" on trying to connect.

Other vulnerable stuff includes the zener diodes intended to clip down
incoming ring voltage, on the transformer "primary" (telco) side.  These
may fail as a short-circuit.  The ring-detect optoisolator may also blow,
and it can simply be removed if you don't need to take incoming calls.

One of my modems actually had the line relay's contacts welded together by
a lightning hit, so it stayed off-hook constantly!  Check the
isolation transformer for a open coil on either side.  If it's a
high-speed modem, be sure to replace blown transformers with
one of about the same type & quality... the ones on 2400-baud modems
usually had poor frequency response/linearity.

Any damage beyond the transformer will be hard to repair w/o a schematic,
since the surface-mount diodes, transistors, etc. damaged may be hard to
ID for replacement on a surface-mount board.  Something blown in this area
may cause slow/error-prone connections, rather than complete failure.
It happened to be with a particularly nasty strike (the one welding the
line relay closed), transforming a 33.6k modem into a 4800 :-(

Oh, and if the modem's completely dead - no response to AT commands--
you're probably out of luck... this means there's damage to the digital
logic, and it's invariably the 200-pin custom ASICs that blow rather that
74xxx buffers.

(From: jlager@tir.com).

My experiences with the front end of answering machines are welded relay 
contacts mostly.  The symptom is usually holding down the line.

  7.15) Identifying and replacing SMD devices

See the document: "Surface Mount (SMD) Transistor/Diode Cross-reference".
If this does not list your device or it is so fried that no markings survive,
you can usually use some educated guesswork to select a suitable replacement.
SMD types can usually be replaced with normal devices since there is usually
sufficient space.  If there are any other SMD parts with the identical marking,
you should be able to determine pinout (e.g., BCE for transistors - see the
document: "Testing of Semiconductor Devices with a DMM or VOM") and replace
with a general purpose non-SMD type.  I doubt that the specifications of parts
used in telephones or modems are critical.  Even if there are no identical
device, if you can determine the voltages on the pins, you may be able to
guess the type.  The worst that will likely happen if you are wrong is to blow
your replacement device - anything that this will do the rest of the circuitry
has already been done.

Chapter 8) Calculators, Clocks, and Watches

  8.1) Problems with calculators

Small hand held and desk calculators share many of the same afflictions
as hand held IR remote controls.  In particular, battery and keypad
problems are common.

Caution: many devices using LCD displays utilize a printed flex cable to
interconnect the electronics and the display.  Often, this is simply glued
to the LCD panel and possibly to the logic board as well.  The cables are
quite fragile and easily torn.  They are also easily ripped from the adhesive
on the LCD panel or logic board.  If the unit is fairly old, this adhesive
may be very weak and brittle.  Repair or replacement should this occur is
virtually impossible.  The material used for the conductors is a type of
conductive paint that cannot be soldered.  It may be possible to use a similar
material like the conductive Epoxy used to repair printed circuit boards
but this would be extremely tedious painstaking work.  Be extremely careful
when moving any of the internal components - LCD, logic board, keyboard,
battery holder/pack, and printer.

The following problems are likely:

1. Batteries - one or more cells are dead, weak, or have leaked.  Try a new
   set if normal primary cells (e.g., alkaline) are used.  Clean the battery
   contacts.  Where rechargeable (usually NiCd) batteries are used, one or
   more cells may have shorted resulting in a dead calculator or dim display,
   or printer that doesn't work reliably.  See the chapter: "Batteries".
   Test each cell after charging for the recommended time or overnight.
   NiCd cells should be about 1.2 V when fully charged.  If any are 0 V, the
   cell is shorted.  This is particularly likely with a unit that has been
   left in a closet unused for an extended period of time.  It is generally
   recommended that the entire battery pack be replaced rather than a single
   cell as the others are probably on their way out and the capacities will
   not be equalized anyhow.  Rechargeable batteries may be the cause of a
   calculator that does not work properly on AC power as well since they are
   usually used like a large filter capacitor and shorted cells will prevent
   the required DC voltage from being provided to the electronics.  Open cells
   or bad battery connections will prevent this filtering as well and may
   result in erratic operation or other symptoms.  For this reason, it may
   not be possible to run a unit of this type reliably or at all with the
   rechargeable batteries removed.

   Some calculators that use rechargeable batteries like older HPs and TIs
   have a battery pack of 24.4 to 3.6 V with a DC-DC inverter to obtain the
   9 V or so that the NMOS chipset required.  These rarely fail except
   possibly due to leakage of neglected dead batteries.  However, good
   batteries need to be in place for the calculator to work properly.  If
   you are not interested in using these types of calculators on batteries,
   disconnect the DC=DC convertor and substitute a suitable AC adapter.
   Check the voltage and current requirements for your particular model.

2. Keypad - dirt, gunk, and wear may result in one or more keys that are
   intermittent or bounce (result in multiple entries).  Disassemble, clean
   and restore the conductive coating if necessary.  See the document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls".

3. Printer (where applicable) - in addition to replacing the ribbon when
   the print quality deteriorates, cleaning and lubrication may be needed
   periodically.  Dust, dirt, and paper particles collect and gum up the
   works.  Clean and then relube with light machine oil or grease as
   appropriate.   Sometimes, gears or other parts break resulting in
   erratic operation or paper or other jams.  Locating service parts is
   virtually impossible.

4. AC adapter - if the calculator does not work when plugged into the
   AC line, this may be defective - broken wires at either end of the
   cord are very common.  However, shorted cells in an internal NiCd
   battery will likely prevent the proper voltage from being supplied to
   the electronics even when using AC power since the battery is often
   used like a large filter capacitor at the same time it is being
   charged.  Open cells or bad connections to the battery pack may result
   in erratic operation or other symptoms as well.

   Don't overlook the obvious: are you using the proper adapter and if
   it is a universal type, is the polarity and voltage set correctly?
   Check the specifications.  With the proliferation of AC adapters, it
   is all to easy to accidentally substitute one from another device.

  8.2) Repairing a calculator (or other device) with a fried power transformer

There may be a thermal fuse under the outer layers of insulation with is
the only casualty.  It is worth checking out.

(The specific example below is for a Sharp desktop calculator, model CS-1608.
It has a power transformer with 6 wires on the secondary: 2 red, 2 yellow,
1 orange, and 1 brown.)

Power surges, overheating, or connecting a 115 V device to a 220 V line can
all blow the primary.  An overload could also but is likely not the problem.
In my experience, it seems that the transformers in these things are designed
so close to core saturation that excess voltage will not be transferred to
the secondary and even plugging a 115 transformer device like a digital clock
into a 220 line will not kill the logic, but just melts the transformer
primary.  I have a bag full of the things (including a cordless phone) which
were damaged in this manner when someone decided to do a little house
rewiring.  You can guess the rest.

As far as the calculator goes, there are probably 2 sets of secondary
windings probably with centertaps - check it with a multimeter.  I would
guess that the brown is the centertap for the reds and the orange is the
centertap for the yellows but simple tests will confirm or refute this.
One may be for the logic and the other for the printer motors, LCD, who

Obviously, if you can obtain an exact replacement, **this** is truly the
best solution.  Short of this, try to find someone who can measure the
secondary voltages on a working model of this calculator.  Then, you could
replace the transformer with a pair of readily available transformers with
suitable ratings.

If you feel on the lucky side and can at least determine which wires go with
which windings, you could carefully bring up power on one output and see if
there is any response.  It will be at least 5 V.  Examining the regulation
circuitry and filter capacitors could also provide a clue.  Also, you could
determine the ratio of the secondaries by powering one from a low voltage
AC source and measuring the output of the other (assuming the primary isn't
so messed up as to load down the transformer due to shorts).

There are many options besides giving up.

  8.3) Getting inside calculators

Many will have a couple of screws (possibly hidden under rubber feet or inside
the battery compartment) or snaps which will permit the two halves of the case
to be separated.  However, some very popular models are apparently not designed
to be repaired at all:

Note: I have heard that there is a somewhat less destructive (but not any
easier) procedure for getting inside HP48s than that given below but have
not seen it.

(From: A.R. Duell (ard12@eng.cam.ac.uk)).

Have you ever tried to open up an HP48 (or just about any HP calculator later
than the 71B)? It's non-trivial to do non-destructively - these darn things
are held together by pegs that were melted over after the case was assembled.

From memory (and I've never actually done a 48, just the smaller ones) you
have to:

1. Remove batteries, cards, etc.

2. Carefully peel off the metal overlay on the keyboard. This can be done
   without putting a fold in it, but it takes practice.

3. Use a 4 mm (I think) drill held in the fingers to remove the tops of the
   moulded studs holding the case together

4. Pull off the back part of the case.

You can now see the circuit board. It's held down by twisted metal tabs.  The
keyboard is under it, and is held together by a lot more of those infernal
moulded studs.

  8.4) Battery powered digital clock problems

First, try a fresh battery and clean the battery contacts if necessary.
If the battery is very low or dead, well....  When the battery is low
or the connections are bad, the countdown logic may run erratically - fast
as well as slow.  Give it a week and then see if the problem still exists.

If it does - and the error is only a few minutes a week - then an adjustment
may be all that is needed.  If the error is much worse - like it is running
at half speed - then there is a problem in the logic - time for new clock
(or at least a new movement).

There should be a recessed screw for fine speed adjustment accessible from
the back - possibly after a sticker or outer cover is removed.  It may be
marked with a couple of arrows and if you are lucky, with the proper
direction for speed increase and decrease.

Without test equipment, the best you can do is a trial and error approach.
Turn the screw just the tiniest bit in the appropriate direction.  If this
is not marked, use counterclockwise to slow it down and vice-versa.

Wait a week, then readjust if necessary.

If you have frequency counter with a time period mode, you can try putting
it across the solenoid terminals and adjusting for exactly 1.000000 second.
Hopefully the load of the counter will not affect the oscillator frequency.

With sensitive equipment, it may even be possible to do this without any
connections by detecting the fundamental frequency radiation of the quartz
crystal oscillator and adjusting it for exactly 32,768 Hz (most common).

However, keep in mind that the clock's quartz crystal accuracy required to
gain or lose less than 1 minute a month is about +/- 1 part in 43,000 which
may be better than that of your frequency counter's timebase.  One
alternative is to perform the same measurement on a clock that is known
to be accurate and then match the one you are adjusting to that.

  8.5) AC powered digital clock problems

Common problems include totally dead, missing segments in display, running
at the wrong rate, switches or buttons do not work.  (Also applies to the
clock portions of clock radios.)

Note that these is often a battery - possibly just an 9V alkaline type
for backup in the event of a power failure.  If this is missing or dead,
any momentary power interruption will reset the clock.

Although a totally dead clock could be caused by a logic failure, the
most likely problem is in the power supply.  The power transformer may
have an open winding or there may a bad connection elsewhere.  A diode
may be defective or a capacitor may be dried up.

Often, the secondary of the power transformer is center tapped - test
both sides with a multimeter on its AC scale.  Typical values are
6-15 VRMS.  If both sides are dead, then the primary is likely open.
There may be a blown fusable resistor under the coil wrappings but a
burnt out primary is likely.  Although generic replacement transformers
are available you will have two problems: determining the exact voltage
and current requirements (though these are not usually critical) and
obtaining a suitable regulatory (UL. CE, etc) approved transformer -
required for fire safety reasons.

If the transformer checks out, trace the circuit to locate the DC outputs.
These power supplies are usually pretty simple and it should be easy to
locate any problems.

Missing segments in the display are most likely caused by bad connections.
Try prodding and twisting the circuit board and inspect for cold solder

A clock that runs slow on 50 Hz power or fast on 60 Hz power may not
be compatible with the local line frequency since these clocks usually
use the power line for timing rather than a quartz crystal.  This is
actually a more precise (as well as less expensive) approach as the power
line frequency long term accuracy is nearly perfect.  Sometimes there is
a switch or jumper to select the line frequency.

Dirty switches and buttons can be cleaned using a spray contact cleaner.

  8.6) Why is my $2 LED clock so much more accurate than the clock in my $2,000 PC?

Computer clocks use a crystal and are not tied to the AC line - after all,
they have to keep time even when the computer is unplugged.  Cheap digital
clocks that plug into the AC line are extremely accurate - better than anything
else you are likely to have access to short of the broadcast time signal.

The reason for this is that the power line frequency is referenced to an
atomic clock somewhere and its long term accuracy is therefore maintained
to great precision.  Even the short term frequency stability is very good,
changing by at most a small fraction of 1 percent due to variations in
electric load affecting generator speed (U.S national power grid - isolated
areas with local power generators could see much much wider swings).

These clocks may not keep good time if (1) the power line is very noisy, (2)
there is a power outage, or (3) they are broken.  Power line noise on the same
circuit might confuse some clocks, however.  This might happen with light
dimmers or universal motors (e.g., vacuum cleaners, electric drills, etc.) on
the same circuit.

  8.7) Replacing batteries in digital watches

About the only type of service you can expect to perform is battery
replacement but even this can save a few dollars compared to taking
the watch to a jeweler.  The typical watch battery will last anywhere
from a year (alkaline) to 5 years (lithium).  The most likely cause of
a watch that has a dead or weak display, or has stopped or is not
keeping proper time is a weak or dead battery.

The batteries (actually single cells) used in most modern watches (they
used to be called electric watches, remember the Accutron?) are either
alkaline or lithium button cells.  Some are quite tiny.  You will need to
open up the watch to identify the type so that a replacement can be

How you go about doing this will depend on the watch:

1. Screws.  If there are visible screws on either the front or rear, then
   removing these will probably enable the cover to be popped off.  These
   will be teeny tiny star (sort of Philips) head type - use a precision
   jeweler's screwdriver with a Philips head tip.  Immediately put the
   screws into a pill bottle or film canister - they seem to evaporate on
   their own.

2. Snap off back.  This is probably most common.  Look for an indentation
   around the edge.  Using a penknife or other similar relatively sharp
   edged tool in this indentation or at any convenient spot if there is
   none.  It is best to use the wristband mounting rod as a lever fulcrum
   if possible.  The back should pop off.  Note the orientation of the back
   before you set it aside so that you can get it back the same way.

3. Cover unscrews.  The entire back may be mounted in a screw thread around
   its edge in which case you will have to somehow grab the entire back
   and rotate counter clockwise.  An adjustable wrench with some tape to
   protect the finish on the watch may work.

If there is an O-ring seal (like on the space shuttle), be careful not to
nick or otherwise damage it (you know what happens when these are damaged!).

Once the back is off, you will see a lot of precision stuff - though not 
nearly as much as in an old fashioned mechanical watch.  DON'T TOUCH!
You are interested in only one thing - the battery.  Sometimes, once the
back is off, the button cell will simply drop out as there is no other
fastener.  In other cases, one or two more teeny tiny screws will hold it
in places.  Carefully remove these and the button cell.  Replace the screws
so you will not loose them.  Make a note of the orientation of the button
cell - it is almost always smooth side out but perhaps not in every case.

Test the battery with a multimeter.  The voltage of a fresh battery will
be about 1.5 V for an alkaline cell and as high as 3 V for a lithium cell.
A watch will typically still work with a battery that has gone down to
as little as half its rated voltage.

Replacement batteries can be obtained from Radio Shack, some supermarkets,
large drug outlets, electronic distributors, or mail order parts suppliers.
Most likely, you will need to cross reference the teeny tiny markings
on the old battery - places that sell batteries usually have a replacement

Cost should be about $2.00 for a typical alkaline cell and slightly more
for the longer lived lithium variety.

Note: some watches bury the battery inside the works requiring further 
disassembly.  This is usually straightforward but will require additional
steps and some added risk of totally screwing it up.

Install and secure the replacement battery and immediately confirm that
the display is alive or the second hand is moving.  If it is not, double
check polarity.  Sometimes, the back will need to be in place for proper
contact to be made.

Chapter 9) Photographic Equipment

  9.1) Light meters

First check the batteries (if any).  Self powered meters like the old
Westons and their clones could also cause damage to the delicate meter
movement if the light regulating lid was left open in bright light.
Bad connections were also common.  I have repaired the meter movements
on these but it is not much fun.

Hand held light meters are subject to damage from being dropped.

Problems with internal light meters include bad batteries and corroded
battery contacts, dirty or worn potentiometers.

  9.2) Pocket camera repair

It seems that in the last few years, the amount of circuitry crammed into
a compact 35 mm camera has grown exponentially.  Auto-film-advance, auto-
exposure, auto-film speed detection and loading, auto focus, auto-flash
selection, auto-red-eye reduction - just about everything that could be
put under computer control has been.  Next thing you know, the photographer
will be replaced with a auto-robot!

For the most part, modern cameras are very reliable.  However, when something
goes wrong, it is virtually impossible to attempt repair for two reasons:

1. The circuitry is so crammed into a tiny case that access is difficult and
   convoluted.  Many connections are made with relatively fragile flexible
   printed cables and getting at certain parts means removing a whole bunch
   of other stuff.

2. Much of the circuitry is surface mount and many custom parts are used.
   Schematics are nearly impossible to obtain and with all the computer
   control, probably not that useful in any case.  Most parts are not
   available except from the manufacturer and then possibly only to
   authorized service centers.

However, some problems can be addressed without resorting to the camera
repair shop or dumpster.

If the camera is still under warranty, don't even think about attempting
any kind of repair unless it is just a bad battery.  Almost certainly,
evidence of your efforts will be all too visible - mangled miniature screw
heads and damaged plastic seams - at the very least.  There are no easy
repair solutions.  Let the professionals deal with it.

If out of warranty and/or you don't care about it and/or you want an
excuse to buy a new camera, then you may be able to fix certain (very
limited) types of problems.

  9.3) Getting inside a pocket camera

For anything beyond the battery, you will need to get inside.  However,
before you expend a lot of effort on a hopeless cause consider that
unless you see something obvious - a broken connection, bent or dirty
switch contact, or a motor or other mechanical part that is stuck, binding,
or in need of cleaning and lubrication - there is not a lot you will likely
be able to do.  One exception is with respect to the electronic flash which
is usually relatively self contained and simple enough to be successfully
repaired without a schematic.

As with other consumer electronics equipment, getting inside may be a
challenge worthy of Sherlock Holmes.  In addition to many obvious very
tiny screws around the periphery, there may be hidden screws inside the
battery compartment and under the hand grip (carefully peel it back if
that area is the last holdout).  Also see the section: "Getting inside consumer electronic equipment".

This is the time to make careful notes and put all the tiny parts in
storage containers as soon as they are removed.  If you never follow
any of these recommendations for other types of equipment, at least
do so for pocket cameras!

Caution: the energy storage capacitor for the electronic flash may be located
in an unexpected spot way on the other side of the camera.  Accidentally
touching its terminals when charged will be unpleasant to say the least.  Even
if the camera is 'off', some designs maintain this capacitor at full charge.
In addition, it may retain a painful charge for days - with the battery
removed.  Once you get the skins off of the camera (if you ever succeed),
identify this capacitor - it will be about the size of a AA battery - and
put electrical tape over its terminals.

  9.4) Pocket camera problems

The following malfunctions may sometimes be successfully dealt with
without an army of camera repair technicians at your disposal:

Caution: never open the back of a 35 mm camera anywhere there is light of
any kind if there is a chance that there is film inside.  If the camera
is dead, there may be no way of knowing.  Doing this even for an instant
may ruin all of the film that has been exposed and two (usually) additional
pictures.  Opening the back of any other kind of roll film camera will
only expose a few frames as the exposed film usually has a backing (120)
or is inside a cartridge (110).

If a 35 mm camera failed with a roll of film on which you have taken
irreplaceable photographs inside, the pictures can still be saved even if
the camera never works again.  First, wash your hands thoroughly to
remove skin oils.  Use a closet with a tightly fitting door (at night is
better or stuff something in any cracks to block all light - it must be
pitch black) for a darkroom.  Open the back of the camera and carefully
remove the film cassette.  Gently pull the exposed film from the takeup
spool (on the shutter release side of the camera).  It should unwind
easily.  Avoid touching the film surface itself with your fingers (the
edges are ok).  Then, turn the plastic shaft sticking out of the film
cassette clockwise to wind the exposed film entirely into the cassette.

(For items (2)-(4), you will need to get inside of the camera.  See the
section below: "Getting inside a pocket camera".)

1. General erratic or sluggish operation, weak display, camera pooped out
   during film advance or rewind.  Most likely cause: the battery died.

   Test the battery and/or try a new one.  It is possible that the
   battery simply decided to go flat at an inconvenient time or that
   a replacement was defective.  If possible, check the voltage on the
   battery while it is in the camera and the affected operations are
   performed.  If the voltage drops substantially, there could be an
   overload - a motor that is binding or a shorted component.  If the
   camera had been dropped, a mechanical problem is likely.

2. Flash inoperative or excess current drain - runs down batteries.
   Other functions may or may not work correctly.  Most likely cause: a
   shorted inverter transistor.  The electronic flash or strobe is
   usually a self contained module near the actual flash window but
   the energy storage capacitor may be mounted elsewhere - like the
   opposite side of the case.  See the warning below - you could be
   in for a surprise!

3. Mechanical problems with focus, exposure, film advance, or rewind.
   Likely causes: binding due to damage from being bumped or dropped,
   bad or erratic motor operation, gummed up lubrication or dirt, or
   defective driver or control logic.  Locate the motor for each
   function (right, good luck) and confirm that they spin freely and
   move the appropriate gears, levers, cogs, wheels, or whatever.  If
   there is any significant resistance to movement, attempt to determine
   if it is simply a lubrication problem or if something is stuck.  Test
   the motors - see the section: "Small motors in consumer electronic equipment".

4. Auto-film-loading, film advance, or rewind do not operate at all or do
   not terminate.  Most likely cause: defective motor or mechanical problems,
   dirty, corroded, or faulty sensor switches or bad controller.  If there
   is no action or something seems to get stuck or sounds like it is
   struggling, check the battery and motor (see (1) and (3) above).
   Inspect the various microswitches for broken actuators, bent or deformed
   contacts, or something stuck in them like a bit of film that broke away
   from the roll.  Dirt may be preventing a key contact closure.  Sometimes,
   improper cable routing during manufacture can interfere with the free
   movement of a leaf type contact.

5. Exposure too light or too dark.  Check the film speed setting and/or clean
   the contact fingers under the cassette that sense the film (ASA or ISO)
   speed.  Clean the light meter sensor.  Check the batteries,  Look for
   evidence of problems with the lens iris and/or shutter mechanism.  If
   the shutter speed can be set manually, see the section: "Testing of camera shutter speed".

6. Automatic camera not responding to adjustments.  Changing the diaphragm
   or shutter speed usually moves a variable resistor which is part of the
   exposure computer.  If a single control has an erratic effect or no effect,
   its variable resistor is likely dirty or broken.  If none of the controls
   behave as expected, there may be a problem in the actual circuitry that
   computes the exposure.  There is little chance that you could repair such
   a fault.  First, replace the batteries.  Some of these systems will behave
   strangely if the batteries are weak.

Unless there is something obvious - the diaphragm control is not engaging
the lever of the variable resistor, for example, and you care about the
future health of your camera, my recommendation would be to take it in for
professional service.

To successfully repair modern sophisticated compact cameras requires that you
be really really experienced working on teeny tiny mechanisms, have the proper
precision tools (e.g., good quality jeweler's screwdrivers, not just the $2
K-Mart assortment), bright light and a good magnifier, and a great deal of
patience and attention to detail.

  9.5) Testing of camera shutter speed

If you suspect shutter speed problems, there are several easy ways to
measure this for your camera.  The most accurate require some test
equipment but you can get a pretty good idea with little or no equipment
beyond a stopwatch (for slow shutter speeds - above 1/2 to 1 second and a
TV (for fast shutter speeds - below about 1/60 of a second (NTSC 525/60).

Some of these approaches assume that you have access to the film
plane of the camera - this may be tough with many highly automated
compact cameras which will be unhappy unless a roll of film is
properly loaded with the back door closed.

Note that the behavior of focal plane and leaf (in-the-lens) shutters
is significantly different at high shutter speeds and this affects the
the interpretation of measurements.

Some simple homemade equipment will enable testing of the intermediate
shutter speeds.

1. Testing slow to medium shutter speeds - the use of a stopwatch is self
   evident for really long times (greater than .5 second or so).  However,
   viewing or photographing the sweep hand of a mechanical stop watch
   or a homemade motor driven rotating white spot or LED can provide quite
   accurate results.  Accurate timing motors are inexpensive and readily
   available.  Mount a black disk with a single small white spot at its
   edge on the motor shaft and mark some graduations around its perimeter
   on a stationary back board.  For a high tech look, use an LED instead.
   Use your creativity.

   Making measurements from the photographic images of the arcs formed
   by the spot as it rotates while the shutter is open should result in
   accuracies better than 1 or 2% for shutter speeds comparable to or slower
   than the rotation frequency of the motor.  In other words, shutter speeds
   down to 1/10th of a second for a 600 rpm (10 rps) motor or down to 1/60th
   of a second for a 3600 rpm (60 rps) motor.

   At these speeds, focal plane and leaf shutters should result in similar
   results since the open and close times are small compared to the total
   exposure time.

2. Testing fast shutter speeds - view a TV (B/W is fine) screen on a piece
   of ground glass at the focal plane or take a series of snapshots of a
   TV screen (a well adjusted B/W TV is best as the individual scan lines
   will be visible).

   Note: If your camera has a focal plane shutter (e.g., 35 mm SLRs), orient
   the camera so that the shutter curtain travels across - horizontally
   (rather than up or down).

   If you are photographing the screen, take a few shots at each speed
   in case the timing of your trigger finger is not quite precise and
   you cross the vertical blanking period with some of them.  This will
   also allow you to identify and quantify any variations in shutter
   speed that may be present from shot-to-shot.

   For a focal plane shutter, you will see a bright diagonal bar.  (The
   angle of the bar can be used to estimate the speed of the shutter
   curtain's traversal.)

   For a leaf (in-the-lens) shutter, you will see a bright horizontal
   bar. but the start and end of the exposure (top and bottom of the bar)
   will be somewhat fuzzy due to the non-zero time it takes to open and
   close the shutter leaves.  You will have to estimate the locations of
   the 'full width half maximum' for each speed.

   In both cases, there will some additional smearing at the bottom of the
   bar due to the persistence of the CRT phosphors.

   The effective exposure time can then be calculated by multiplying the
   number of scan lines in the bar at any given horizontal position by
   63.5 uS (the NTSC horizontal scan time).

   If you cannot resolve individual scan lines, figure that a typical over-
   scanned (NTSC) TV screen has 420-440 visible lines.  If you can adjust
   your TV (remember this can be an old B/W set when knobs were knobs!) for
   underscan, about 488 or so active video lines will be visible.

If you have an oscilloscope or electronic counter/timer, fairly accurate
measurements can be made at all shutter speeds using a bright light and
a photodetector circuit.

3. Using an electronic counter/timer or oscilloscope.  A gated 24 bit counter
   clocked at 1 MHz would permit (ideally) testing shutter speeds from 1/2000th
   second to 16 seconds with an accuracy of better than .2 percent.  Of course
   in practice, the finite size of any photodiode and/or the finite open/close
   time of any shutter will limit this at high shutter speeds.  Any resonably
   well calibrated oscilloscope will be accurate enough for shutter speed

   Construct the IR detector circuit described in the document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls".  (Note that the
   fact that it is called an IR detector is irrelevant since the typical
   photodiode is sensitive to visible wavelengths of light as well.)  Connect
   its output to the minus gate of your counter or the vertical input of your
   scope.  Put a diffuse light source (i.e., light bulb) close to the lens so
   that it is not in focus.  Position the detector photodiode in the center of
   the focal plane - mount it on a little piece of cardboard that fits on the
   film guide rails.  Using this setup, it should be a simple matter to measure
   the shutter timing.  Take multiple 'exposures' to identify and quantify
   any variations in shutter speed that may be present from shot-to-shot.

   For a focal plane shutter, the time response will be the convolution
   of the photodetector area and the slit in the shutter curtain.  The
   smaller the aperture of the photodiode, the less this will be a factor.
   Masking it with black tape may be desirable when testing fast shutter
   speeds.  In simple terms, make the photodiode aperture narrow.

   For between-the-lens shutters, the finite open and close times of the
   leaves will show up on the oscilloscope in the rise and fall times of
   the trace.  The measurement on the electronic timer will be affected
   by its trigger level setting for this reason.  However, since this
   photodetector is not linearly calibrated, the open and close times
   cannot be accurately determined from the waveform.

  9.6) Electronic flash fundamentals

All modern electronic flash units (often called photographic strobes) are
based on the same principles of operation whether of the subminiature
variety in a disposable pocket camers or high quality 35 mm camera, compact
separate hot shoe mounted unit, or the high power high performance unit
found in a photo studio 'speed light'.  All of these use the triggered
discharge of an energy storage capacitor through a special flash tube
filled with Xenon gas at low pressure to produce a very short burst of
high intensity white light.

The typical electronic flash consists of four parts: (1) power supply,
(2) energy storage capacitor, (3) trigger circuit, and  (4) flash tube.

An electronic flash works as follows:

1. The energy storage capacitor connected across the flash tube is charged
   from a 300V (typical) power supply.  This is either a battery or AC adapter
   operated inverter (pocket cameras and compact strobes) or an AC line
   operated supply using a power transformer or voltage doubler or tripler
   (high performance studio 'speed' lights).  These are large electrolytic
   capacitors (200-1000+ uF at 300+ V) designed specifically for the rapid
   discharge needs of photoflash applications.

2. A 'ready light' indicates when the capacitor is fully charged.  Most
   monitor the voltage on the energy storage capacitor.  However, some
   detect that the inverter or power supply load has decreased indicating
   full charge.

3. Normally, the flash tube remains non-conductive even when the capacitor
   is fully charged.

4. A separate small capacitor (e.g., .1 uF) is charged from the same power
   supply to generate a trigger pulse.

5. Contacts on the camera's shutter close at the instant the shutter is
   fully open.  These cause the charge on the trigger capacitor to be
   dumped into the primary of a pulse transformer whose secondary is
   connected to a wire, strip, or the metal reflector in close proximity
   to the flash tube.

6. The pulse generated by this trigger (typically around 10 KV) is enough to
   ionize the Xenon gas inside the flash tube.

7. The Xenon gas suddenly becomes a low resistance and the energy storage
   capacitor discharges through the flash tube resulting in a short
   duration brilliant white light.

The energy of each flash is roughly equal to 1/2*C*V^^2 in watt-seconds
(W-s) where V is the value of the energy storage capacitor's voltage and
C is its capacitance in.  Not quite all of the energy in the capacitor is
used but it is very close.  This energy storage capacitor for pocket cameras
is typically 200-300 uF at 330 V (charged to 300 V) with a typical flash
energy of 10 W-s.  For high power strobes, 1000s of uF at higher voltages
are common with maximum flash energies of 100 W-s or more.  Another important
difference is in the cycle time.  For pocket cameras it may be several
seconds - or much longer as the batteries run down.  For a studio 'speed
light', fractional second cycle times are common.

Typical flash duration is much less than a millisecond resulting in crystal
clear stop action photographs of almost any moving subject.

On cheap cameras (and probably some expensive ones as well) physical contacts
on the shutter close the trigger circuit precisely when the shutter is wide
open.  Better designs use an SCR or other electronic switch so that no high
voltage appears at the shutter contacts (or hot shoe connector of the flash
unit) and contact deterioration due to high voltage sparking is avoided.

Note that for cameras with focal plane shutters, the maximum shutter speed
setting that can be used is typically limited to 1/60-1/120 of a second.
The reason is that for higher shutter speeds, the entire picture is not
exposed simultaneously by the moving curtains of the focal plane mechanism.
Rather, a slit with a width determined the by the effective shutter speed
moves in front of the film plane.  For example, with a shutter speed setting
of 1/1000 of a second, a horizontally moving slit would need to be about
1/10 of an inch wide for a total travel time of 1/60 of a second to cover the
entire 1.5 inch wide 35 mm frame.  Since the flash duration is extremely
short and much much less than the focal plane curtain travel time, only the
film behind the slit would be exposed by an electronic flash.  For shutter
speed settings longer than the travel time, the entire frame is uncovered
when the flash is triggered.

See the section: "Photoflash circuit from pocket camera" for the schematic
of a typical small battery powered strobe.

Red-eye reduction provides a means of providing a flash twice in rapid
succession.  The idea is that the pupils of the subjects' eyes close somewhat
due to the first flash resulting in less red-eye - imaging of the inside of
the eyeball - in the actual photograph.

This may be done by using the main flash but many cameras use a small, bright
incandescent bulb to 'blind' the eyes when the shutter is pressed to meter,
then it goes off and the flash preserves the 'closed' pupils.  This approach
works.  Using the main flash would require sub-second recycle time which is
not a problem if an energy conserving flash is used (see the document: "Notes on the Troubleshooting and Repair of Electronic Flash Units and Strobe Lights".  However, it would add significant additional expense otherwise (as
is the case with most cameras with built in electronic flash).  A separate
little bulb is effective and much cheaper.

Automatic electronic flashes provide an optical feedback mechanism to sense
the amount of light actually reaching the subject.  The flash is then aborted
in mid stride once the proper exposure has been made.  Inexpensive units
just short across the flash tube with an SCR or even a gas discharge tube
that is triggered by a photosensor once the proper amount of light has been
detected.  With these units, the same amount of energy is used regardless
of how far away the subject is and thus low and high intensity flashes drain
the battery by the same amount and require the same cycle time.  The excess
energy is wasted as heat.  More sophisticated units use something like a gate
turnoff thyristor to actually interrupt the flash discharge at the proper
instant.  These use only as much energy as needed and the batteries last
much longer since most flash photographs do not require maximum power.

Failure of red-eye reduction or the automatic exposure control circuits
will probably require a schematic to troubleshoot unless tests for bad
connections or shorted or open components identify specific problems.  It is
also possible for that extra red-eye incandescent light bulb to be burnt out
but good luck replacing it!

Remotely triggered 'fill flashes' use a photocell or photodiode to trigger
an SCR - or a light activated SCR (LASCR) - which emulates the camera shutter
switch closure for the flash unit being controlled.  There is little to go
wrong with these devices.

  9.7) Electronic flash problems

A variety of failures are possible with electronic flash units.  Much
of the circuitry is similar for battery/AC adapter and line powered
units but the power supplies in particular do differ substantially.

Most common problems are likely to be failures of the power supply, bad
connections, dried of or deformed energy storage or other electrolytic
capacitor(s) and physical damage to the to the flashtube.

  9.8) Problems unique to battery or AC adapter powered electronic flash units

* Power source - dead or weak batteries or defective charging circuit,
  incorrect or bad AC adapter, worn power switch, or bad connections.

  Symptoms: unit is totally dead, intermittent, or excessively long
  cycle time.

  Test and/or replace batteries.  Determine if batteries are being charged.
  Check continuity of power switch or interlock and inspect for corroded
  battery contacts and bad connections or cold solder joints on the circuit

* Power inverter - blown chopper transistor, bad transformer, other
  defective components.

  Symptoms: unit is totally dead or loads down power source when switched
  on (or at all times with some compact cameras).  No high pitched audible
  whine when charging the capacitor.  Regulator failure may result in
  excess voltage on the flash tube and spontaneous triggering or failure
  of the energy storage capacitor or other components.

  Test main chopper transistor for shorts and opens.  This is the most
  likely failure.  There is no easy way to test the transformer and the
  other components rarely fail.   Check for bad connections.

  9.9) Problems unique to AC line powered electronic flash units

WARNING: Line powered units often do not include a power transformer.
Therefore, none of the circuitry is isolated from the AC line.  Read,
understand, and follow the safety guidelines for working on line powered
equipment.  Use an isolation transformer while troubleshooting.  However,
realize that this will NOT protect you from the charge on the large high
voltage power supply and energy storage capacitors.  Take all appropriate

* Power source - dead outlet or incorrect line voltage.

  Symptoms: unit is totally dead, operates poorly, catches fire, or blows up.
  Spontaneous triggering may be the result of a regulator failure or running
  on a too high line voltage (if the unit survives).

  Test outlet with a lamp or circuit tester.  Check line voltage
  setting on flash unit (if it is not too late!).

* Power supply - bad line cord or power switch, blown fuse, defective
  rectifiers or capacitors in voltage doubler, defective components, or
  bad connections.

  Symptoms: unit is totally dead or fuse blows.  Excessive cycle time.

  Test fuse.  If blown check for shorted components like rectifiers and
  capacitors in the power supply.  If fuse is ok, test continuity of line
  cord, power switch, and other input components and wiring.  Check
  rectifiers for opens and the capacitors for opens or reduced value.

  9.10) Problems common to all electronic flash units

WARNING: the amount of charge contained in the energy storage capacitor
may be enough to kill - especially with larger AC line powered flash units
and high power studio equipment.  Read and follow all safety guidelines
with respect to high voltage high power equipment.  Discharge the energy
storage capacitors fully (see the document: "Capacitors: Testing with a
Multimeter and Safe Discharging") and then measure to double check that they
are totally flat before touching anything.  Don't assume that triggering
a flash does this for you!  For added insurance, clip a wire across the
capacitor terminals while doing any work inside the unit.

* Energy storage capacitor - dried up or shorted, leaky or needs to be

  Symptoms: reduced light output and unusually short cycle time may 
  indicate a dried up capacitor.  Heavy loading of power source with
  low frequency or weak audible whine may indicate a shorted capacitor.
  Excessively long cycle time may mean that the capacitor has too much
  leakage or needs to be formed. 

  Test for shorts and value.  Substitute another capacitor of similar
  or smaller uF rating and at least equal voltage rating if available.

  Cycling the unit at full power several times should reform a capacitor
  that has deteriorated due to lack of use.  If the flash intensity and
  cycle time do not return to normal after a dozen or so full intensity
  flashes, the capacitor may need to be replaced or there may be some
  other problem with the power supply.

* Trigger circuit - bad trigger capacitor, trigger transformer, SCR (if
  used), or other components.

  Symptoms: energy storage capacitor charges as indicated by the audible
  inverter whine changing frequency increasing in pitch until ready light
  comes on (if it does) but pressing shutter release or manual test button
  has no effect.  Spontaneous triggering may be a result of a component
  breaking down or an intermittent short circuit.

  Test for voltage on the trigger capacitor and continuity of the trigger
  transformer windings.  Confirm that the energy storage capacitor is
  indeed fully charged with a voltmeter.

* Ready light - bad LED or neon bulb, resistor, zener, or bad connections.

  Symptoms: flash works normally but no indication from ready light.  Or,
  ready light on all the time or prematurely.

  Test for voltage on the LED or neon bulb and work backwards to its voltage
  supply - either the trigger or energy storage capacitor or inverter trans-
  former.  In the latter case (where load detection is used instead of simple
  voltage monitoring) there may be AC across the lamp so a DC measurement may
  be deceptive.)

* Trigger initiator - shutter contacts or cable.

  Symptoms: manual test button will fire flash but shutter release has
  no effect.

  Test for shutter contact closure, clean hot shoe contacts (if relevant),
  inspect and test for bad connections, test or swap cable, clean shutter
  contacts (right, good luck).  Try an alternate way of triggering the
  flash like a cable instead of a the hot shoe.

* Xenon tube - broken or leaky.

  Symptoms: energy storage and trigger capacitors charges to proper
  voltage but the manual test button does not fire the flash even though
  you can hear the tick that indicates that the trigger circuit is

  Inspect the flash tube for physical damage.  Substitute another similar
  or somewhat larger (but not smaller) flash tube.  A neon bulb can be put
  across the trigger transformer output and ground to see if it flashes when
  you press the manual test button shutter release.  This won't determine
  if the trigger voltage high enough but will provide an indication that
  most of the trigger circuitry is operating.

  9.11) Electronic flash dead after long time in storage

The unit may be totally dead or take so long to charge that you give up.

For rechargeable units, try charging for the recommended time (24 hours if
you don't know what it is).  Then, check the battery voltage.  If it does
not indicate full charge (roughly 1.2 x n for NiCds, 2 x n for lead-acid where
n is the number of cells), then the battery is likely expired and will need
to be replaced.

Even for testing, don't just remove the bad rechargeable batteries - replace
them.  They may be required to provide filtering for the power supply even
when running off the AC line or adapter.

For units with disposable batteries, of course try a fresh set but first
thoroughly clean the battery contacts.

See the Chapter: "Batteries".

The energy storage capacitor will tend to 'deform' resulting in high leakage
and reduced capacity after long non-use.  However, I would still expect to
be able to hear sound of the inverter while it is attempting to charge.

Where the unit shows no sign of life on batteries or AC, check for dirty
switch contacts and bad internal connections.  Electrolytic capacitors
in the power supply and inverter may have deteriorated as well.

If the unit simply takes a long time to charge, cycling it a dozen times
should restore an energy storage capacitor that is has deformed but is
salvageable.  This is probably safe for the energy storage capacitor as
the power source is current limited.  However, there is no way of telling
if continuous operation with the excessive load of the leaky energy storage
capacitor will overheat power supply or inverter components.

  9.12) Photoflash circuit from pocket camera

This schematic was traced from an electronic flash unit removed from an
inexpensive pocket camera, a Keystone model XR308.  Errors in transcription
are possible.

Note that the ready light is not in the usual place monitoring the energy
storage capacitor voltage.  It operates on the principle that once nearly
full charge is reached and the inverter is not being heavily loaded, enough
drive voltage is available from an auxiliary winding on the inverter
transformer to light the LED.  It is also interesting that the trigger
circuit dumps charge into the trigger capacitor instead of the other way
around but the effect is the same.

           Inverter                                                  Flashtube
      |       1 K     Ready LED      |            S1 Power |  |        |   |
      |   +--/\/\-----+--|<|-----+   |           ______ On |  +-+ T2 +-+   |
 BT1  _   |    R1     |  IL1     |   |          |      \___|     )||(      |
 3 V ___  | || +------|--/\/\/---+   | C1       |    __ Off      )||(     +|FL1
2-AA  _   | ||(2 .4   |  R2 10       | Energy   |   |            )||(     _|_
     ___  | || +-------------+       | Storage  |   +-------+---+ ||(    | | |
      |   | ||(5 .2   |      |      +|  280 uF  |           |     ||(   ||   |
      +---+ || +------+      |     __|__ 330 V  | S2 Fire -|      ||(   ||   |
      |     ||(1      |      |     _____        | (Shutter) |        +--||   |
      +---+ ||(       |  C3  |       |          |     +-----+   Trigger ||   |
          3)||( 142  -|47 uF |      -|          |     |     |           || _ |
       <.1 )||(      _|_ 6.3 |       |          |  R1 \    _|_  C2       |_|_|
           )||(      ___  V  |       |          |  1M /    ___ .02 uF      |
        +-+ || +-+    |      |       |          |     \     |   400 V     -|
       C| 4 T1 6 |   +|      |       |          |     /     |              |
     B|/         |    |      |  D1   |          |     |     |              |
   +--| 2SD879   +--------------|<|--+----------------+-----+--------------+
   |  |\  Q1          |      | HV Rect.         |
   |   E|             |      |                  |
   |    +-------------+------|------------------+
   |                         |


1. The inverter boosts the battery voltage to about 300 V.  This is rectified
   by D1 and charges the energy storage capacitor, C1.

2. The LED, IL1, signals ready by once C1 is nearly fully charged.

3. Pressing the shutter closes S2 which charges C2 from C1 through T2
   generating a high voltage pulse (8-10KV) which ionizes the Xenon
   gas in the flashlamp, FL1.

4. The energy storage capacitor discharges through the flashlamp.


1. The inverter transformer winding resistances measured with a Radio Shack
   DMM.  Primary resistance was below .1 ohms.

       |                                     |
    ---+--- are connected;    ---|--- and ------- are NOT connected.
       |                                     |

  9.13) Darkroom timers

Developing timers only provide a display or clock face (possibly with an
alarm) while enlarging timers include a pair of switched outlets - one for
the enlarger and the other for the safe light.  These are usually self
resetting to permit multiple prints to be made at the same exposure time

Where the device plugged into a controlled outlet does not come on, first
make sure these units are operational (i.e., the bulbs of the enlarger
and/or safelight are not burned out and that their power switches are
in the 'on' position.  The problem could also be that one of these devices is
defective as well.

Two types of designs are common:

1. Electromechanical - using an AC timing motor and gear train with cam
   operated switches controlling the output circuits directly or via relays.

   If the hands fail to move or it does not reset properly, the timing motor
   or other mechanical parts may require cleaning and lubrication.  The
   motor may be inoperative due to open or shorted windings.  See the section:
   "Small motors in consumer electronic equipment".  Where the timer appears
   to work but the controlled outlets (e.g., enlarger and safe light) do not
   go on oroff, check for a loose cam or bent linkages and dirty or worn switch
   or relay contacts.  If the dial fails to reset after the cycle completes,
   it may be binding or require cleaning and lubrication or a spring may
   have come loose or broken.

2. Electronic - digital countdown circuits and logic controlling mechanical
   or solid state relays or triacs.

   Where the unit appears dead, test as with AC line powered digital clocks
   (see the section: "AC powered digital clock problems").  If the buttons
   have the proper effect and the digits count properly but the external
   circuits are not switching, then test for problems in the power control
   circuits.  If the unit is erratic or does not properly count or reset,
   there could be power supply or logic problems.

  9.14) Weird exposure meter problem of the year

Here is one for the photo album:

"Ever since I bought the Mamiya 645 Pro 2 months ago, I've had exposure
 problems. I usually bring any new eqpt up to Twin Peaks (in SF) to test
 for lens sharpness, and overall function. Well my first shots from there
 were 2 stops overexposed, and the meter was reading wrong, so I returned
 the camera for repair, assuming it was broken out of the box. Mamiya went
 over it with a fine tooth comb, and could find nothing wrong with it. I
 got it back on Monday, and went up to Twin Peaks again. Same problem as
 before! The meter read 2 stops over! I cursed the techies at Mamiya, I
 cursed the product, I cursed MF, and then I decided to get scientific
 about it. So I took the camera off the tripod, and pointed it around at
 various things: all normal readings...
 I pointed the camera back at the scene I had just metered on the
 tripod...normal reading. I remounted the camera on the tripod ... 2 stops
 over. I removed the camera ... normal reading. I remounted the camera ...
 2 stops over. Unbelievable. So that's when I started thinking about the RF
 and TV signals being transmitted from the big tower there, and how the
 tripod might act as an antenna, and cause a small current to enter through
 the ground socket and perhaps change the ground reference voltage. But it's
 a carbon fiber tripod! Still, I was on a quest.
 So I borrowed another 645 Pro from the store, and I took my 3 tripods up
 the hill. They were the Gitzo 1228, a Slik U212, and a Tiltall. All 3
 tripods and both cameras exhibited this phenomenon, but to varying
 degrees. The Gitzo was off the most, anywhere from 1-3 stops. The other 2
 did not affect the meter as much, at the most 1-2 stops. Funny thing is,
 the cameras did not even have to *touch* the tripod to have their readings
 affected! As I moved the camera closer, the meter would start overexposing
 by up to a stop, then jump even more once mounted.
 As a control, I then went halfway down the hill, and repeated the test.
 The effect was less, with the Gitzo giving 1-2 stops. I then went
 downtown, and tested again. No difference between on/off camera. I tested
 again when I got home. Again, no difference."

What you have described could indeed be due to RF interference.  Metal and
carbon fiber are both conductors so the construction of the tripods may not
make that much difference.

How is it happening?  This is anyone's guess but enough of a current could
be induced in the sensitive electronic circuitry to throw off the meter.
The ICs are full of diode junctions which can be rectifying (detecting) the
relatively weak RF signal resulting in a DC offset.  If this were the case
and you happened to adjust the tripod height to be around 1/4 wavelength of
one of the transmitters you *would* know it! :-)

Chapter 10) AC Adapters

  10.1) 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: "AC adapter testing".

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 document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies" for more
   info, especially on safety while servicing these units.

Also see the chaper on "Equipment Power Supplies".

  10.2) 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

  10.3) 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.

  10.4) 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.

  10.5) 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 or IC protector 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.

Or, a more dramatic result of the same principles:

(From: Don Parker (tazman@yournet.com)).

A guy brought a Johnson Messenger CB to my shop a few decades back.  He had
been told it would run on 12 VDC *and* 115 VAC - so he tried it!  I never saw
so many little leads sticking up from any pcb since - that once were capacitors
and top hat transistors.  There was enough fluff from the caps to have the
chassis rated at least R-10 :->).

  10.6) Power reversal - better pray

"That's right, I reversed power and ground on a Sony XR-6000 AM/FM cassette
 car stereo. (12V negative ground).
 The little fellow made a stinky smell, so I assume that at least one
 component is cooked."
If it had not been turned on before you discovered your error, the damage
may have been limited to the display and some filter caps.  Then again...

The problem is that an auto battery has a very high current capacity and
any fuses respond too slowly to be of much value in a situation such as
this.  Any capacitors and solid state components on the 12 V bus at the
time power was applied are likely fried - well done.

"Is there any hope of my repairing it?  (This assumes I show more ability
 than I did when installing it.)  Which part(s) are likely damaged?"

(From: Onat Ahmet (onat@turbine.kuee.kyoto-u.ac.jp)).

Well, based on that last statement ;-) 

BAD: car batteries can provide amps and amps of current (much worse than
     reverse connecting a wall adapter for example.)

GOOD: The stinking might be due to a component getting too hot
      and vaporizing the solder paste/preserver/dust on it, but
      not actually giving up the ghost.

      I would find and check any fuses, or components directly
      in-line with or parallel to the power lines (the latter
      might include the IC's unfortunately...)

GOOD: There might have been a protecting diode somewhere (but why
      did it stink then (^_^)

NEUTR: Did you disassemble it to see if there were any blackened
       areas/components? Smell from a close distance; I can often
       locate a burnt component that way even after a long time.

If not, join the happy crowd, and gut the good old stereo for parts!

  10.7) 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
  internal fault like a short circuit or external fault like a prolonged
  overload condition.

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!

  10.8) 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.

To convert such an adapter to DC requires the use of:

    * Bridge rectifier - turns AC into pulsating DC.
    * Filter capacitor - smooths 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.

  10.9) 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.

For an arbitrary voltage between about 1.2 and 35 V 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 the 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.

Chapter 11) Equipment Power Supplies

  11.1) AC (plug-in) power supplies

Reread Safety info before tackling any power supply problem in a VCR!

If your equipment uses an AC adapter (wall wart), see the Chapter: "AC Adapters" first.

Consumer electronic equipment typically uses one of four types of power
supplies (There are no doubt others):

1. Power transformer with linear regulator using 78/79XX ICs or discrete
   components.  The power transformer will be large and very near the
   AC line cord.

2. Power transformer with hybrid regulator like STK5481 or any of its
   cousins - multioutput with some outputs switched by power on.  If it
   has one of these, check ECG, SK, or NTE, or post to sci.electronics.repair
   and someone can probably provide the pinout.  Again, the power transformer
   will be large and very near the AC line cord.

3. Small switching power supply.  Most common problems: shorted semiconductors,
   bad capacitors, open fusable resistors.  In this case there is usually
   no large power transformer near the line input but a smaller transformer
   amidships.  This is rare in audio equipment as the switching noise is
   difficult to keep out of the audio circuits.  These are more often found
   found in some VCRs, TVs, monitors, fax machines, and printers.

Some comments for each type:

1. Troubleshooting is quite straightforward as the components are readily
   identified and it is easy to trace through from the power transformer,
   bridge or centertapped full wave rectifiers, regulators, caps, etc.

2. Failures of one or more of the outputs of these hybrid regulators
   are very common.  Use ECG/STK/NTE cross reference to identify the correct
   output voltages.  Test with power switch in both positions.  Any
   discrepancy indicates likely problem.  While an excessive load dragging
   down a voltage is possible, the regulator is the first suspect.
   Replacement cost is usually under $10.

3. Switching supplies.  These are tougher to diagnose, but it is possible
   without service literature by tracing the circuit and checking for
   bad semiconductors with an ohmmeter.  Common problems - dried up
   capacitors, shorted semiconductors, and bad solder joints.   See the
   document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies" for more detailed information.

  11.2) Totally dead power supply (non-switching type)

Don't overlook the possibility of bad solder connections or even a
bad line cord or plug.  Maybe Fido was hungry.

First, make sure the outlet is live - try a lamp.  Even a neon circuit
tester is not a 100% guarantee - the outlet may have a high resistance
marginal connection.

Check for blown fuses near the line cord input.  With the unit unplugged,
test for continuity from the AC plug to the fuse, on/off switch and power
transformer.  With the power switch in the 'on' position, testing across
the AC plug should result in a resistance of 1 to 100 ohms depending on
the size of the equipment (see the section: "Internal fuse blew during lightning storm (or elephant hit power pole)" for typical resistance 
readings of transformer primary windings.

If the fuse blew and the readings are too low, the transformer primary may
be partially or totally shorted.  If the resistance is infinite even directly
across the primary of the power transformer, it may be open or there may be
an open thermal fuse underneath the outer layer of insulation wrapping.

If the fuse blew but resistance is reasonable, try a new fuse of the proper
ratings.  If this blows instantly, there is still a fault in the power supply
or one of its loads.  See the section: "About fuses, IC protectors, and circuit breakers".

If these check out, then the problem is likely on the secondary side.
One or more outputs may be low or missing due to bad regulator components.
A secondary winding could be open though is is less common than primary side
failure as the wire (in transistorized equipment at least) is much thicker.

  11.3) Low or missing power supply outputs (non-switching type)

Once the line input and primary circuits have been found to be good (or at
have continuity and a resistance that is reasonable, the problems is
most likely in the secondary side - fuses, rectifiers, filter capacitors,
regulator components, bad connections, excess load due to electronic
problems elsewhere.

Depending on the type of equipment, there may be a single output of several
outputs from the power supply.  A failure of one of these can result in
multiple systems problems depending on what parts of the equipment use what

Check for bad fuses in the secondary circuits - test with an ohmmeter.  (I
once even found an intermittent fuse!)  Try a new fuse of the same ratings.
If this one blows immediately, there is a fault in the power supply or one of
its loads.  See the section: "About fuses, IC protectors, and circuit breakers".  The use of a series current limiting resistor - a low wattage
light bulb, for example - may be useful to allow you to make measurements
without undo risk of damage and an unlimited supply of fuses.

Locate the large electrolytic filter capacitor(s).  These will probably be
near the power transformer connections to the circuit board with the power
supply components.  Test for voltage across each of these with power on.  If
they are in pairs, this may be a dual polarity supply (+/-, very common
in audio equipment).  Sometimes, two or more capacitors are simply used
to provide a higher uF rating.  If you find no voltage on one of these
capacitors, trace back to determine if the problem is a rectifier diode,
bad connection, or bad secondary winding on the power transformer (the
latter is somewhat uncommon as the wire is relatively thick, however).

Dried up electrolytic capacitors will result in excessive ripple leading
to hum or reduced headroom in audio outputs and possible regulation
problems as well.  Test with a scope or multimeter on its AC scale (but
not all multimeters have DC blocking capacitors on its AC input and these
readings may be confused by the DC level).  If ripple is excessive - as a
guideline if it is more than 10 to 20% of the DC level - then substitute
or jumper across with a good capacitor of similar uF rating and at least
the same voltage rating.

If you find voltages that are lower than expected, this could be due to bad
filter capacitors, an open diode or connection (one side of a full wave
rectifier circuit), or excessive load which may be either in the regulator(s),
if any, or driven circuitry.

Disconnect the output of the power supply from its load.  If the voltage
jumps up dramatically (or the fuse now survives or the series light bulb
now goes out or glows dimly), then a short or excess load is likely.

If the behavior does not change substantially, the problem may be in the
regulator(s).  Transistors, zener diodes, resistors, and other discrete
components, and IC regulators like LM317s or 7809s can be tested with an
ohmmeter or by substitution.  The most common failures are shorts for
semiconductors, opens for resistors, and no or low output for ICs.

Where the supply uses a hybrid regulator like an STK5481, confirming
proper input and then testing each output is usually sufficient to
identify a failure.  A defective hybrid regulator will likely provide
no or very low output on one or more outputs.  Confirm by disconnecting
the load.  Test with any on/off (logic) control in both states.

  11.4) Uninterruptible power supplies (UPSs) and power inverters

Caution: reread safety guidelines as portions of these devices can be nasty.

Note: inexpensive UPSs and inverters generate a squarewave output so don't
be surprised at how ugly the waveform appears if you look at it on a scope.
This is probably normal.  More sophisticated and expensive units may use
a modified sinewave - actually a 3 or 5 level discrete approximation to a
sinewave (instead of a 2 level squarewave).  The highest quality units
will generate a true sinewave using high frequency bipolar pulse width 
modulation.  Don't expect to find this in a $100 K-Mart special, however.

A UPS incorporates a battery charger, lead-acid (usually) storage battery,
DC-AC inverter, and control and bypass circuitry.

Note that if finding a UPS that provides surge protection is an important
consideration, look for one that runs the output off of the battery at all
times rather than bypassing the inverter during normal operation.  The battery
will act as a nearly perfect filter in so far as short term line voltage
variations, spikes, and noise, are concerned.

A DC-AC power inverter used to run line powered equipment from an automotive
battery or other low voltage source is similar to the internal inverter in
a UPS.

For a unit that appears dead (and the power has not been off for more than
its rated holdup time and the outlet is live), first, check for a blown
fuse - external or internal.  Perhaps, someone was attempting to run their
microwave oven off of the UPS or inverter!

(See the section on: "Fuse post mortems" to identify likely failure mode.)

If you find one - and it is blown due to a short circuit - then there are
likely internal problems like shorted components.  However, if it is blown
due to a modest overload, the powered equipment may simply be of too high
a wattage for the UPS or inverter - or it may be defective.

Failures of a UPS can be due to:

1. Battery charging circuit - if the battery does not appear to be charging
   even after an extended time, measure across the battery with the unit both
   unplugged and plugged in.  The voltage should jump up some amount with
   power on - when it is supposed to be charging.  Disconnect the battery
   and try again if there is no action - the battery may be shorted totally.
   Check for blown fuses, smoked parts, and bad connections.

2. Battery - deteriorated or abused lead acid batteries are very common.
   If the battery will not charge or hold a charge, battery problems are
   likely.  A UPS (or any kind of lead-acid battery powered equipment) that
   lies idle for a long time (say a year or two) without power to top off
   the battery will likely result in a dead - not salvageable - battery due
   to sulfation.  Symptoms will be: voltage on battery climbs to more than
   2.5 V per cell when first put on charge and even after a long charging
   period, the battery has essentially no capacity.  If the battery voltage
   is at its nominal value - even when the inverter should be running from it
   (and there is no or low output), then there is a problem in the inverter
   or its connections or there is excess load.

3. Inverter - troubleshooting is similar to that required for a switchmode
   power supply.  Common problems: shorted power semiconductors, open fusable
   resistors, dried up electrolytic capacitors, and bad connections.  See the
   document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies".  A visual inspection may reveal parts that have exploded or
   lost their smoke.

4. Line bypass circuit (if used) - check for problems in the controller
   or its standby power supply, or power switchover components, and bad

  11.5) About fuses, IC protectors, 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 (i.e., excess volume to loudspeakers).

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
consisting of a glass (or sometimes ceramic) body and metal end caps.  The
most common sizes are 1-1/4" mm x 1/4" or 20 mm x 5 mm.  Some of these have
wire leads to the end caps and are directly soldered to the circuit board but
most snap into a fuse holder or fuse clips.  Miniature types include: Pico(tm)
fuses that look like green 1/4 W resistors or other miniature cylindrical or
square varieties, little clear plastic buttons, etc.  Typical circuit board
markings are F or PR.

IC protectors are just miniature fuses specifically designed to have a
very rapid response to prevent damage to sensitive solid state components
including intergrated circuits and transistors.  These usually are often
in TO92 plastic cases but with only 2 leads or little rectangular cases
about .1" W x .3" L x .2" H.  Test just like a fuse.  These may be designated
ICP, PR, or F.

Circuit breakers may be thermal, magnetic, or a combination of the two.
Small (push button) circuit breakers for electronic equipment are most
often 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 electro-
magnet 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.

  11.6) Fuse post mortems

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.

  11.7) 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 venture 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.

Four 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.
   It is safe to use a replacement with equal or high voltage rating.

3, 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.

4. 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 a fuse will have wire leads and be soldered directly onto the
   circuit board.  However, your own wires can be carefully soldered to the
   much more common cartridge type to create a suitable replacement.

  11.8) 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 :-),

  11.9) Identifying the connections on an unknown power transformer

Start with a good multimeter - DMM on the lowest ohms scale or VOM on the
X1 resistance range.  (You will need to be able to measure down to .1 ohms
for many of these.)  This will permit you to map the windings.

First, identify all connections that have continuity between them.  Except for
the possible case of a water soaked transformer with excessive leakage, any
reading less than infinity on the meter is an indication of a connection.  The
typical values will be between something very close to 0 ohms and 100 ohms.

Each group of connected terminals represents one winding.  The highest reading
for each group will be between the ends of the winding; others will be lower.
With a few measurements and some logical thinking, you will be able to
label the arrangement ends and taps of each winding.

Once you do this, applying a low voltage AC input (from another power
transformer driven by a Variac) will enable you to determine voltage ratios.
Then, you may be able to make some educated guesses as to the primary and
secondary.  Often, primary and secondary windings will exit from opposite
sides of the transformer.

For typical power transformers, there will be two primary wires but
international power transformers may have multiple taps as well as a
pair or primary windings (possibly with multiple taps) for switching
between 110/115/120 VAC and 220/230/240 VAC operation.  Typical color
codes for the primary winding(s) will be black or black with various
color stripes.  Almost any colors can be used for secondary windings.
Stripes may indicate center tap connections but not always.

Note: for safety, use the Variac and another isolated transformer for this.

  11.10) Determining unknown connection on international power transformers

Most likely, you can figure this out if you can identify the input connections.

There will be two primary windings (resistance between the two will be
infinite).  Each of these may also have additional taps to accommodate
various slight variations in input voltage.  For example, there may
be taps for 110/220, 115/230, 120/240, etc.

For the U.S. (110 VAC), the two primary windings will be wired in parallel.
For overseas (220 VAC) operation, they will be wired in series.  When
switching from one to the other make sure you get the phases of the two
windings correct - otherwise you will have a short circuit!  You can test
for this when you apply power - leave one end of one winding disconnected
and measure between these two points - there should be close to zero voltage
present if the phase is correct.  If the voltage is significant, reverse
one of the windings and then confirm.

A multimeter on the lowest resistance scale should permit you to determine
the internal arrangement of any taps on the primaries and which sets of
secondary terminals are connected to each winding.  This will probably
need to be a DMM as many VOMs do not have low enough resistance ranges.

It is best to test with a Variac so you can bring up the voltage gradually
and catch your mistakes before anything smokes. 

You can then power it from a low voltage AC source, say 10 VAC from your
Variac or even an AC wall adapter, to be safe and make your secondary
measurements.  Then scale all these voltage readings appropriately.

  11.11) 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).

  11.12) 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.  

For the advanced course:

(From Winfield Hill (hill@rowland.org)).

We know there are many things you can learn about a fully potted transformer.
Certainly the turns ratio (from ratio of ac input-output voltage), and the
magnetizing and leakage inductances can be easily measured.  With some
assumptions about the core material (which may actually be visible at some
spot), we can move on to an estimation of the number of turns, which with the
DC resistance tells us the likely wire size...  calculating winding fill area
as a double check, we can hone in on possible core gaps.  Next, measuring
primary core saturation further illuminates the earlier guesses about the core
material, gaps and windings.  By the time one is finished with this process it
may be possible to have a rather complete description of the transformer,
allowing not only for more accurate engineering with it, but also its
replication or improvement for your task.

  11.13) 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.

  11.14) 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

Chapter 12) Batteries

  12.1) 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 convertor 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.

  12.2) 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.

  12.3) 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.

  12.4) 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.

  12.5) 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 connot 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.

  12.6) 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:

        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 farily constant until very near the end.

  12.7) 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."

  12.8) 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.

  12.9) 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.  

  12.10) 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 densrites 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.

Is my battery charging?

If you are trying to substitute a battery of a different type, all bets may
be off.  For example, NiCd and lead-acid are quite different in operation
and termination conditions.  Thus, your charger may not be fully charging the
new pack for some reason or one or more of the cells may be defective.

If you can, monitor both current and voltage into the battery during charging.
The voltage should top out somewhat over the marked ratings.  The current
should work out to around 1.5 times the A-h rating over the charging period.
If this is the case, put a load on the battery and see if you get something
near the A-h rating out.

  12.11) 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

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.

  12.12) 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, Dust Busters, 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).

  12.13) Identifying technology of umarked 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.

  12.14) 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.

  12.15) 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 (even
those with fancy warranties and high budget advertising) 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 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).

One 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 in a hurry).
Nickel Cadmium cells contain so-called heavy metal compounds which are also
bad for you if you feast on them but can be safely cleaned up without harm.

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 use an emery board, 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 alternative 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.

Don't forget that many batteries do come with explicit or implicit warranties
against leakage (and resulting damage) which cover the equipment they are in
as well.  Thus, you may be able to obtain a replacement device from the battery
manufacturer for at most shipping charges.  I don't know if this extends to
expensive products like palmtop computers :-).

  12.16) 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 when loads like the radiator fan
or air conditioner are switched on or off.

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) and 20 A or more without blowing a fuse.  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.

For something like a CD player that runs on a 9VDC wall adapter, even if the
droid at Radio Shack says it will work without dropping the voltage, proceed
with caution.

The 3 V difference isn't the only problem - you might get away with that
though I would recommend against it (measure the open circuit voltage out of
your AC adapter - it is probably closer to 12 V or more anyhow).  It is the
other nastiness of the automotive power.

Putting 4 diodes (e.g., 1N4002) in series with the power would drop the
voltage to be closer to 9 V but the spikes will sail right through

If it were mine, I would probably add some filtering to the 12 V - maybe
10,000 uF, 35 V, and then use a 7809 or LM317 regulator to drop it to 9 V.
This isn't a guarantee but is much better than ignoring the issues entirely.
See the section: "Adding an IC regulator to a wall adapter or battery".

However, there is a one more minor problem - when starting, the voltage can
easily drop to 9 V or less.  With the regulator, the output would be closer to
7 V which may or may not be enough.  So, the player may quit while starting
but I suppose there are more important things to worry about!

As with a laptop, another option is to use a small 12 VDC to 115 VAC inverter,
perhaps $25.  This would definitely protect the player (assuming the adapter
doesn't mind the squarewave it puts out) but would not be very efficient.

I received a dead CD player with an auto adapter included.  It was supposed
to run on 3 V.  Guess what?  There was no circuitry in the adapter!  That
was probably a Radio Shack recommendation as well :-).  Just because the
plugs match doesn't mean it will work and not blow up!

  12.17) 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!

Chapter 13) Motors and Relays

  13.1) Small motors in consumer electronic equipment

A variety of motor types are found in audio and other electronic equipment.
For the additional information on the specific types of motors used in
VCRs and CD players, see the documents: "Notes on the Troubleshooting and Repair of Video Cassette Recorders" and "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives".

Types of motors:

1. Small brush-type permanent magnet (PM) DC motors similar to those found
   in battery operated appliances.  Such motors are 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.

   These 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. 

   Also see the section: "General tape speed problems - slow, fast, or dead".

   Additional info on these types of motors can be found in "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives".

2. A low profile or 'pancake' brushless DC motor may provide power for a
   in some Walkman type tape players, direct drive capstans and general
   power in VCRs or tape decks.   Since these are electronically controlled,
   any non-mechanical failures are difficult to diagnose.  In some cases,
   electronic component malfunction can be identified and remedied.

3. AC induction motors - shaded pole or synchronous type used in inexpensive
   turntables.  These motors are extremely reliable and are easy to
   disassemble, clean, and lubricate.  Just do not lose any of the
   spacer washers on each end of the shaft and make notes to assure
   proper reassembly.

4. Miniature synchronous motors 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.

  13.2) Motor noise in audio equipment

Of course you expect your audio equipment to be absolutely silent unless
told to perform.  Motor noise should not be objectionable.  However, what
if it is?  There are several kinds of noise: rotating noise, vibration,
and electrical interference:

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 electronic equipment".

For AC motors and transformers, 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.

If the noise - a buzz or whine - is actually coming from the audio output
but only occurs with the motor running, the interference filter on the
motor power supply may have failed.  This is often just a capacitor across
the motor terminals and it may be defective or there may be a bad connection.

  13.3) 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 - for tape players and turntables - this may not be feedback
   controlled.  With a little care you should be able to determine the 
   normal rpms of the motor.  For example, with a cassette deck, knowing
   the tape speed (1-7/8" inches per second is standard), it is
   straightforward calculate the motor shaft speed based on simple
   measurements of pulley and capstan diameter ratios.

MCM Electronics, Dalbani, and Premium Parts stock a variety of generic
replacement motors for tape decks, Walkmen, boomboxes, and CD players.

  13.4) Relay basics

The ubiquitous electromechanical relay is a device that is used in a large
variety of applications to switch power as well as signals in electrical
and electronic equipment.  Operation is quite simple:  An electromagnet
powered by an AC or DC coil pulls on an armature having a set of moving
contacts which make or break a connection with a set of stationary contacts.

Most common relays can be characterized by three sets of parameters:

1. Coil - voltage; resistance, current, or power consumption; and whether it
   is AC or DC.  For AC coils only, the VA (volt-amps) rating may be used
   instead of or in addition to power consumption due to the inductive coil.
   Typical coil voltages range from 5 V to 480 V (AC or DC) - and beyond.
   Current and power consumption depend on the size of the relay.

2. Contact configuration - number of sets of contacts and whether they
   are their type.  The designation will be something like SPST-NO, DPDT,
   4PST-NC, 6PDT, etc.  The first two letters refers to the number of sets
   of simultaneously activated contacts (S=1, D=2, numbers are usually
   used for more than 2 sets of contacts).  The second two letters refers
   to the contact configuration (ST=NO or NC but no common terminal, DT
   will have a common - there will be both an NO and NC terminal).  Where
   contacts are ST, the last two letters indicate NO or NC.  An almost
   unlimited number of variations are possible.  Typical relays have
   anywhere from 1 to 6 or more separate sets of ST or DT contacts or a
   mixture of the two.

3. Contact ratings - this may be specified for a number of types of
   applications.  For example: in amperes at a particular voltage for DC
   resistive loads, or in horsepower at various voltages for AC inductive
   loads.  Like fuse ratings, these are maximum ratings and lower values
   are almost always acceptable.  Small relays may be able to switch
   only a few hundred mA at 32 V while large industrial contactors can
   switch 1000s of A at 1000s of V.  Even the contactor in your automobile's
   starter must control hundreds of amps to the starter motor.

The common (C) contacts connect to the normally closed (NC) contacts when
the coil is unpowered and to the normally open (NO) contacts when the coil
is powered.

Miniature and subminiature relays are used to switch phone line signals
in modems, fax machines, and telephone answering machines; audio amplifier
speaker protection circuits; multiscan monitor deflection components; and
many other places.

Small relays control power in lighting equipment, TVs and other home
appliances, automotive systems and accessories, and the like.

Large relays (often called contactors) are used for the control of central
air conditioning systems (compressor and blower motors), all types and sizes
of industrial machinery - as well as in the starter of your automobile.

  13.5) Relay identification

A relay without a pin connection diagram can usually be identified with
a multimeter and variable power supply - or by eye.  Many have the critical
information printed on the cover.  However, for detailed specifications,
referring to the manufacturer's databook (or WEB page) really is best!

(The following assumes a subminiature (DIP) relay.  Lower coil resistances,
higher coil voltages, and other variations may exist for larger relays.)

1. If the case of the relay is transparent or you can pop the top, examine
   the pole piece of the electromagnet.  If there is a (copper) ring around
   half the pole piece, the relay coil is designed for AC (usually line
   frequency - 50 or 60 Hz) operation.  An AC relay operated on DC will
   overheat very quickly but can be tested on DC.

2. Determine the coil pins.  Use your eyeball if possible or your multimeter
   on the low resistance scale.  For a small relay, the coil will most likely
   be a few hundred ohms.  All other combinations of pins will be zero or
   infinity.  If the resistance is under, say, 100 ohms, you may have an AC
   coil rather than a DC coil.

3. Power the relay from a variable DC supply (I am assuming it has a DC
   coil which is likely for a DIP relay.  You can still do this with an
   AC coil but it will heat up quickly).  Start at zero and increase the
   voltage until you hear the contacts close.  This will probably be at
   around 3 volts (for a 5 V coil) or 8 volts for a 12 V coil - this will be
   roughly 60% of nominal coil voltage.  If you do not hear anything,
   reverse the polarity of the coil and try again - you may have a latching
   relay.  Alternatively, put your multimeter on the resistance scale
   across one of the pairs of pins that measured zero ohms as it is likely
   to be a NC set of contacts.  This will change to infinity ohms when
   the relay switches.

4. Now that you can switch the relay on and off, you can use your multimeter
   on the resistance scale to determine which contacts are normally open
   (NO) and which contacts are normally closed (NC).  (Normally here means

5, The power rating of the contacts can be estimated by their diameter (if
   they are visible).  Rough current estimates (resistive loads): 20 A - 5 mm,
   10 A - 3 mm, 5 A - 2 mm, 1 A - 1 mm.  These must be derated substantially
   for inductive loads.

For latching relays, the polarity of the coil voltage determines whether the
relay is switched on or off.  In other words, to switch to the opposite
state requires the polarity of the voltage to the coil to be reversed.  Other
types are possible but not very common.

  13.6) Relay testing and repair

If the relay is totally inoperative, test for voltage to the coil.  If the
voltage is correct, the relay may have an open coil.  If the voltage is low
or zero, the coil may be shorted or the driving circuit may be defective.
If the relay makes a normal switching sound but does not correctly control
its output connections, the contacts may be corroded, dirty, worn, welded
closed, binding, or there may be other mechanical problems.

Remove the relay from the circuit (if possible) and measure the coil
resistance.  Compare your reading with the marked or specified value
and/or compare with a known working relay of the same type.  An open
coil is obviously defective but sometimes the break is right at the
terminal connections and can be repaired easily.  If you can gain access
by removing the cover, a visual examination will confirm this.  If the
resistance is too low, some of the windings are probably shorted.  This
will result in overheating as well as no or erratic operation.  Replacement
will be required.

Relay contacts start out bright and shiny.  As they are used, arcing,
dirt, and wear take their toll.  A sealed relay used at well below its
rated current with a resistive load may work reliably for millions of cycles.
However, this will be significantly reduced when switching high currents -
especially with inductive loads which results in contact arcing.  One speck
of dirt can prevent a contact from closing so cleanliness is important.
Excessive arcing can result in the contacts getting welded together as well.

The resistance of closed contacts on a relay that is in good condition
should be very low - probably below the measurable limits on a typical
multimeter - a few milliohms.  If you measure significant or erratic
resistance for the closed contacts as the relay is switched or if very
gentle tapping results in erratic resistance changes, the contacts are
probably dirty, corroded, or worn.  If you can get at the contacts, the
use of contact cleaner first and a piece of paper pulled back and forth
through the closed contacts may help. Superfine sandpaper may be used as
a last resort but this is only a short term fix.  The relay will most likely
need to be replaced if the contacts are switching any substantial power.

Chapter 14) General Equipment

  14.1) IC and hybrid power audio amplifiers

Note: troubleshooting of large audio amplifiers constructed with discrete
output stages is left to a separate document.  See: "BIG audio power amps".

The audio amplifiers found in small radios, Walkmen, portable cassette
recorders, and other low power devices are often single chips with few
external components.  Obtain a pin diagram, test inputs and output(s) with
an audio signal tracer and/or oscilloscope.  A dead output where inputs
and power are present usually indicate a defective IC - as does one that
becomes excessively hot - assuming that the output is not overloaded.

Larger audio amplifiers may use ICs (up to 10 or 20 W) or hybrid modules
(up to 100 W per channel and beyond).  Purists may argue about the quality
of the sound from these compared to discrete component designs but they
are being used in many designs - at most price points (except perhaps the
stratosphere of audiophile land).

Hybrids modules (called 'blocks' or 'bricks' by some) may be totally self
contained requiring just power and line level inputs or may be just the
final stage in an overall system including external amplifier circuitry
which is  effectively a power op amp - high gain with negative feedback.
Failure of these bricks is quite common.

Note that testing of these op amp designs - whether discrete or brick
based - can be very confusing due to the high gain and feedback.
Intermediate signals in a working channel may look like power supply
ripple and noise.  In a dead channel these same points may appear to be
normal or highly distorted audio depending on which stage you test.  In
addition, since extensive negative feedback is used, power supply ripple
and noise is much less important significant and there may be substantial
amounts of both in a normally operating amplifier.

One of the bricks may be shorted resulting in a blown fuse or overheating
of other components.  It is usually safe to unsolder each of the hybrids
to determine if the other channel or at least other portions of the unit
come back to life and without blowing fuses.

With stereo amplifiers, it is normally safe - and most effective - to
swap components between the working and dead channels as long as you
are sure there is no short circuit on the output.  This is by far the
quickest way to confirm a dead brick.  (I would be a lot more reluctant
to make this recommendation for a large audio amplifier constructed
with discrete transistors in the final power stage as multiple cascade
failures are possibly and likely if **all** defective parts are not
located before power is reapplied.)

  14.2) Amplifier noise caused by bad hybrid bricks?

There can be all sorts of sources for low level noise or static including bad
connections almost anywhere, defective semiconductors, and erratic power amp
modules.  These are usually hybrid circuits - multiple devices mounted on a
common substrate and interconnected via a variety of technologies.  Think
of them as entire subsystems encased in plastic.

Thus, hybrid bricks may have problems with noise especially considering that
they may run hot and be abused by poor tastes in music (or at least high
volume levels).  Thermal cycling can take its toll on this kind of device.
If you have eliminated other likely causes, replacing the brick would be the
next step if the module is not that expensive -  how much do you value your
time and hair?  Of course, if there are separate bricks for each channel,
one channel is most affected, and the volume control does not affect the
level of the noise, the choice is clear - swap.  This will be relatively low
risk in most cases.  A hot air gun used carefully on the final modules might
also be a good way of inducing or changing symptoms resulting from marginal
connections or components.

  14.3) Andy's quick tips for locating shorted/bad amplifier parts

(From: Andy Cuffe (baltimora@psu.edu)).

If it has IC's for the audio output you can just remove one of them.  If
the fuse still blows try removing the other one.  If the fuse blows with
both output ICs out you know there are problems in an other part of the
unit, probably the power supply.

If it uses transistors instead of ICs you just need to check them with
an ohmmeter.  The bad ones almost always measure close to 0 ohms
between at least 2 of the three pins.  Once you find the bad pair try
the stereo with them removed.  You should get normal sound from the
channel with the good transistors.  To determine if there is more damage
to the amplifier you can swap the good transistors into the damaged
channel.  Before you remove anything WRITE DOWN where they go because
it's easy to get them mixed up.  I strongly recommend that you don't
bypass the fuse unless you don't want to fix it very much.  I have seen
a lot of repairable electronics ruined by this type of troubleshooting.

  14.4) Substituting Darlington transistors in audio amplifiers

(From Daan van der Veer (D.J.C.vanderVeer@stm.tudelft.nl)).

I have good experiences with the use of Darlingtons instead of normal output
transistors in audio power amplifiers.  The only problem is that you have to
readjust the bias current of the bases of the drivers.  Furthermore, reduced
or increased frequency response is almost always corrected by the amplifier's

Readjusting the bias current is very simple with a scope and a sine wave
generator, but could also be done with a simple voltmeter.  And a computer
is a very handy tool in diagnosing amps, if you have a soundcard, you can
(mis)use it to measure a frequency response of any everyday amp (frequency
response of most soundblaster compatible soundcards is 44 kHz). And with a
very precisely tuned high quality notch filter you can even measure the THD
of any amp, *real-time*.  (This is very handy if you want to adjust output
transistor bias current, to a minimum of crossover distortion).

  14.5) Noisy or intermittent switches and controls

Symptoms include audible noise when rotating knobs, erratic operation of
mode selectors, random changes in volume, switches, or controls that
need to be jiggled or tapped to make them cooperate.

The causes are likely to be either dirt or wear.

First, try a spray control/contact cleaner - even the stuff from Radio Shack
may make a remarkable difference iff (1) dirt is the problem and (2) you can
get the cleaner inside the troublesome part.

DO NOT use WD40 or a similar product because aside from the flammability
issues their use may result in rapid failure even if you get the immediate
gratification often provided by these sprays.  See the section: "Why NOT to use WD40 on noisy controls".

Some types of contact and control cleaners can be used safely with
low voltage circuits while they are powered but not always - read the
label directions.  Select a product that specifically states that is it
safe for switches and controls.

Use the extension tube that comes with the spray can and snake it into
or near any visible access holes.  Operate the control or switch to
help the cleaning action.  Don't overdoe it - if you get to the right
spot, a little is all that is needed.

Resist the urge to use sandpaper or steelwool (ack!) on switch or connector
contacts.  However, pulling a piece paper through a set of contacts or the
occasional gentle use of a soft pencil eraser (e.g., Pink Pearl) may be

If this does not help - or only helps short term - the part may be worn.
Sometimes, repair is possible (a slide switch with contacts that have
loosened with use, for example) but replacement is better - if you can
find an exact or suitably close match.  See the section: "Interchangeability of components".

  14.6) Why NOT to use WD40 on noisy controls

This may not apply to the resistive elements in all/many/most controls but
why risk it?:

(From: Richardson (rchvid7@flash.net)).

Here are some facts after seeing the results first hand in an environment
where Pro TV editors were using up controls in audio mixers manufactured by
Shure Brothers.  WD40 when used for the first time resulted in good operation
for 5 days.  After that time the controls started to deteriorate very quickly
and were junk the next week.

The situation was clear after opening up the pots afterward.  The carbon
material was bonded to itself and to the phenol substrate by some chemical
which became soft after being exposed to the hydrocarbon base of the WD40.  It
soon deteriorated to mush.

The use of LPS 1 did not cause such a dramatic failure of the surfaces but did
not provide any improvement that lasted.

In the past we could get good results with Freon cleaning spray, but it is
getting harder to get than the replacement controls.

In test pots the only way to get an improvement was to carefully remove
residue and relubricate with a lubricant like Radio Shack "Gel Lube" or the
latest Sony grease available for broadcast and pro use.

  14.7) Resuscitating potentiometers

(From: Rene Zuidema (cps_rjz@cistron.nl)).

Often, pots are not really dirty, but the pot wiper just worn out
the resistive layer. No amount of cleaning will solve the problem.

Just carefully re-bend the wiper contacts to follow another track
alongside the damaged resistive material. If done well, the wiper will
now track intact resistive material again. As new!

This specially works for servo's as used in RC cars / planes etc. In
these applications the resistive track around the servo neutral
position is worn out after some seasons of use.

(From: Paul Weber (webpa@aol.com)).

Disassemble the pot by carefully bending the tabs that hold the cover on
(assuming this is a cheap consumer type pot).  Inspect the works with a
magnifying glass; find the fingers on the rotor that touch the resistor
material. Using a needle or dental pick carefully bend the fingers out of
the furrow they've worn in the resistor material.  Objective is to make
contact with an unworn area on the resistor material.  Clean the whole
thing with spray cleaner and re-assemble.

Overall resistance may be slightly changed due to the lost resistance
material, but this is usually not a problem in consumer applications. 
Good luck!

  14.8) General intermittent or erratic behavior

Any intermittent problems that cause random sudden changes in performance
are likely due to bad connections, internal connectors that need to be
cleaned and reseated, or dirty switches and controls.  First, see the
section: "Noisy or intermittent switches and controls".

Bad solder joints are very common in consumer electronic equipment due both
to poor quality manufacturing where cost reduction may be the most important
consideration.  In addition solder connections deteriorate after numerous
thermal cycles, vibration, and physical abuse.  Circuit board connections
to large hot parts or parts that may have mechanical stress applied to them
are most likely be suffer from hairline solder fractures (often called
'cold solder joints' when they result from poor quality soldering at the
time of manufacture).  However, since the solder is often the only thing
anchoring these components, mechanical stress can eventually crack the
solder bond as well.

To locate cold solder joints, use a strong light and magnifier and examine
the pins of large components and components that are subject to physical
stress (like headphone jacks and power connectors) for hairline cracks
in the solder around the pin.  Gently wiggle the component if possible (with
the power off).  Any detectable movement at the joint indicates a problem.
A just perceptible hairline crack around the pin is also an indication of a
defective solder connection.   With the power on, gently prod the circuit
board and suspect components with an insulated tool to see if the problem
can be effected.

When in doubt, resolder any suspicious connections.  Some device may
use double sided circuit boards which do not have plated through holes.
In these cases, solder both top and bottom to be sure that the connections
are solid.  Use a large enough soldering iron to assure that your solder
connection is solid.  Put a bit of new solder with flux on every connection
you touch up even if there was plenty of solder there before.

In addition to soldering problems, check for loose or corroded screw type
ground (or other) terminals, and internal connectors that need to be cleaned
and reseated.

  14.9) Need to turn up volume to get sound to come on

If at times, it is necessary to turn the volume way up or possibly to tap
or whack the unit to get the sound in one or both channels to come on when
the unit is first powered up, the speaker protection relay could be faulty.
Receivers and audio amplifiers often include a set of relay contacts in series
with each output to protect the loudspeakers from power-on and power-off
transients as well as damage due to a fault in the audio circuits.  However,
these contacts may deteriorate after awhile resulting in intermittent sound.

While this set of symptoms could be the result of general bad connections or
even dirty controls or switches, the relay is often at fault.  This is
exacerbated by switching the unit on and off at high volume levels as well
as this may cause contact arcing.

To determine if the relay is at fault, either test it as outlined in the
section: "Relay testing and repair" or with the unit on, very gently tap the
relay to see if the sound comes as goes.  If the relay is bad, you can try
cleaning its contacts or replace with one that has similar electrical
specifications as long as you can mount is somehow.  Don't be tempted to
bypass the relay as it serves a very important protective function for both
the amplifier and your loudspeakers.

If it is not the relay, see the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".

  14.10) Speakers take a while to come on

You turn on your stereo receiver and everything appears normal - display,
tuning, signal strength, etc., but there is no sound.  A few minutes later,
just when you had entirely given up any hope, there is a click and everything
is normal - until the next time you power down.  The amplifier is taunting
you - hehe, I will come on when I feel like it!

(Note that if it never comes on, then there could be a real problem that the
protection circuitry is catching such as shorted components in one of the
power amplifiers.)

This sounds like the signal to power the speaker relays is not being generated.
The underlying cause could be a fault in the time delay or fault protection
(overload) circuit.

It could be as simple as a bad capacitor.  A first test might be to check
for an audio signal at the input to the speaker relay.  If there is signal
almost as soon as you power it up, then trace back from the relay coil to
see what type of circuitry is there.  A schematic will probably be needed
unless you find an obvious bad connection or dried up capacitor.

  14.11) Amplifier clicking and shutting down on music peaks

(From: Frank Fendley (frank.fendley@datacom.iglou.com)).

It sounds like the protection circuit (usually a relay) is cutting in during
louder music passages.  This is caused by an imbalance in the amplifier
circuitry, generally resulting in a DC offset voltage appearing on the output.
The usual cause is a defective transistor(s), probably in the earlier stages
in this case.

Of course, it could also be that you have 10 sets of speakers connected
to the amplifier and all the volume levels turned to the stops - it is
simply protecting itself from abuse! :-) --- sam.

  14.12) Speaker outputs do not come on or shut off immediately

(From: Ronald Dozier (dozier@strauss2.udel.edu)).

The protection relay usually detects DC offset at the speaker terminals
and then open's the speaker leads.  Check for a DC offset > 100 mV or so
before at the output, before the protection relays.

Leaky outputs are the first to suspect.

In most PP drivers the voltage between the bases of the output transistors
should be about 2 Vbe or around 1.2 volts.  0V is definitely a problem.  I
have only seen one amp (mine) that used 4 Vbe. or about 3.2 volts.
The voltage across the emitter resistors without a load are in the 0 to 20 mV
range.  This voltage should not increase appreciably over time and is set with
the bias adjustment.  Careless playing with the bias pot will result in output
transistor destruction.  It is best set with the aid of a distortion analyzer. 

All resistors/transistors in the driver and output stage and in some cases the
pre-amp are all suspect.  The small valued ones like to change value.
Compare with functioning channel.

  14.13) Dead channels on front-end audio components

Unlike big amplifiers, these are not normally failures caused by abuse or
high power components.  This type of equipment includes preamps, cassette
decks, CD players, tuners, etc.

First, eliminate the audio patch cables by trying a different set or swapping
left and right at both ends.  In addition, confirm that your amplifier is
operating on all cylinders (or channels).

Assuming this does not turn up anything:

For a tuner, the problem is almost certainly very near the output - probably
a bad connection, bad jack, or bad final IC or transistor stage.  There isn't
much between the demodulator and the line output.

For a tape deck, much more can be involved.  First, clean any mechanical
REC/PLAY mode and other switches with contact cleaner as dirty contacts
may result in one channel dropping out.  If this does not help, determine
if the output of the tape head is making it to the toutput by touching the
terminals on the playback head with a tiny screwdriver when in play mode -
you should get a hum when you are on the appropriate signal wire.  If there
is none for the bad channel, then you will have to either trace forward from
the head or backward from the output.  If you do hear a hum in the defective
channel, the tape head itself may be bad - shorted or open - very dirty.

Older tuners, receivers, premaps, tape decks, etc. used discrete transistors
and circuit tracing was possible.  Modern equipment relies on ICs but pinouts,
at least, are generally available by checking a cross reference guide such
as those put out by ECG, NTE, or SK.

Again, first eliminate bad jacks or cables -- and with tape decks - clean
the REC/PLAY (and other) mode selector switches.

  14.14) Equipment hums or buzzes

Assuming there are no other symptoms and the sound is coming from inside
the unit and not the loudspeakers, this is probably simply due to vibrating
laminations in the power transformer or motor(s) or nearby sheetmetal that
is affected by the magnetic fields from the power transformer or motor(s).
Most of the time, this is harmless but can definitely be quite annoying
especially when one expects total silence from their audio equipment.
If the noise is coming from any motors or their vicinity, refer to the
section: "Motor noise in audio equipment".

Sometimes, simply tightening the screws that hold the transformer or motor
together or the mounting screws will be all that is needed.  Placing a
toothpick or piece of plastic in a strategic location may help.  It is
also possible to coat the offending component with a varnish or sealer
suitable for electronic equipment but be careful not to use so much that
cooling is compromised or getting any in bearings or locations that would
interfere with rotating parts.

Dirty power - a light dimmer on the same circuit - may also result in increased
magnetic noise.  See the section: "Dirty power and buzz from equipment".

If the hum or buzz is in the audio, there could be a bad filter capacitor
in the power supply, other power supply problems, bad grounds inside the
unit or general ground problems with external equipment, or other bad
connections.  Disconnect all external devices (except the speakers if you
do not have a pair of headphones) and determine if the problem still exists.
Proceed accordingly.  Some Sony receivers are known to develop bad grounds
internally and just tightening the circuit board mounting screws and/or
resoldering ground connections will cure these.

Overloads can also cause a hum or buzz but would generally result in other
symptoms like a totally or partially dead amplifier, severe distortion, smoke,
six foot flames, etc.

If the problem is only annoying when the equipment is not in use, as a last
resort (where no memory or clock functions run off the AC line), putting in
an AC line switch may not be such a bad idea.

  14.15) Dirty power and buzz from equipment

Power line waveforms that are not sinusoidal can cause buzz.  Multiple
devices on the same circuit (or even different circuits) can interact.
A TV or other equipment may add to the problem since its switching power
supply draws current only on part of each cycle.

Excessive voltage can also increase the 'magnetic noise' from motors and
power transformers.  This sound is a result of core or winding vibrations.

You need to check for both of these possibilities - a calibrated scope is
best.  DMMs and VOMs may not read correctly with non-sinusoidal waveforms.

  14.16) Identifying and correcting sources of interference

Although this is a rather special application, similar problems and solutions
apply to other interference problems.  Also see the section: "Interference on AM radio band".

"I am using a 12V DC to 110 VAC converter in my car, to run a small TV/VCR.
 It works fine.  But the TV speaker is not very good.

 So I got one of those cassette adapters that has an audio cassette on one
 end, and a headphone jack on the other.  I plug that into the TV, and the
 cassette slot on my car stereo.  So then I can hear the TV sound on the
 car speakers, which are much better speakers.  

 But now there is a lot of high frequency noise that way, on the car speakers.
 It is very irritating.  A high frequency buzz of some kind.  How can I reduce
 or eliminate that noise?"

(From Duncan (duncan@punk.net)).

First we have to figure out where it is coming from.  The inverter is certainly
a noise source, and without spending a large sum for a well filtered inverter
you have to deal with the noise somehow.

One possibility is that the noise is on the 12 volt power supply going to your
car stereo.  To test for this, play a blank tape while running the TV and
listen for the same noise.  Fix with filters on the power leads of stereo
and/or inverter, wire to a solid clean rail very close to the battery.

Another possibility is capacitive coupling between the TV, connected to the
higher voltage side of your inverter, and the tape deck's playback heads.  This
might be alleviated by using a different, more isolated inverter or by using
another method of getting the audio into the stereo system.  FM modulators
intended for portable CD players might work.

Another possibility is that the power supply of the television is not rejecting
the higher frequency components of the inverter's signal.  The fix here would
be to add more capacitors and perhaps resistive or inductive filter elements
inside the television.  Check this by plugging headphones into the same jack
and listening for the noise.

Still another possibility is that the noise you hear is part of the horizontal
sync signal, which is not rejected well by all televisions.  This causes a high
pitched continuous squeal which is inaudible to some people.  The only easy
work-arounds here would be to try a different television or to turn down the
treble or select Dolby-B on your car stereo.  To test for this effect, try the
same hookup in your house with your home stereo, cassette deck, adaptor
cassette, and television.

Or just hook up your HiFi stereo VCR to the home stereo, move the whole mess
into the car, and ignore the car stereo.  Four of Radio Shack's little Pro-7
speakers with a Marantz 25 watt by four channel amplifier worked quite well
for me, especially when combined with a hand-held LCD monitor :-).

  14.17) Interference on AM radio band

This sort of problem is usually in the form of a buzz or hum at 60 Hz or 120
Hz (or 50 Hz or 100 Hz if your power is at 50 Hz).  There may be a little of
this on a small portion of the AM band but if it is excessive and interferes
with even strong stations, then a remedy is needed!  The following approach
should serve to locate the source if it isn't obvious:

(From: Doug (dslosty@pipeline.com)).

First, turn off the main house breakers and listen on AM with a battery
operated portable radio.

If the noise has disappeared, then you are generating the interference
in your own home and its time to check out things like light dimmers,
fluorescent lamps, touch-control incandescent lamps, motors, even cordless
phones, etc.

If the interference is still present on the portable AM radio, with the
breakers off, walk around the perimeter of the house and see if it's loudest
near the electric service entrance.

If it is, walk up and down the street and try to see if the intensity varies
(your neighbors will think you're weird - but what the heck!).

If the interference comes from outside of your home, it's time to call
the electric utility company and ask to speak with one of their
engineers.  The electric industry is required by the U.S. FCC. to
keep radio interference (RFI) to a minimum.  They may try to stonewall
you but if you persist, they will sent out an engineer with radio
direction finding equipment to locate the source of the interference.
If the source is a piece of equipment on a non-cooperative neighbor's
property, you may have another problem - but - one step at a time.

I've been through this procedure several times. Last time, the electric
company engineer tracked it to a broken and arching pole insulator.

As a former AM broadcast engineer (and current HAM radio operator),
I've experienced this problem enough to know that while challenging,
the interference source can always be found.

(From: Mr Fixit (mrfixit@cyberhighway.net)).

Radio Shack sells RF chokes. Label says "SNAP-ON FILTER CHOKES (2) cat. no.

They open up and snap together over your wires. Very simple to install and
come with comprehensive instructions.

With a little experimentation you can see if you need it on your power
cord, on the speaker wires or both. (these wires can act as antennas for
certain frequencies of RFI)

I use them all over my house on phones, TV's, stereos, computer speakers
etc to block out RFI from my CB base station and vis-versa.

BTW: if you happen to have any unneeded computer monitor cables laying
around, the oversize collar near the end is a RF choke. I had a couple so I
cut the covering and slid them off the cable. I put them onto our cordless
phone base unit antenna as an experiment to see if it would reduce the
ever-present buzz it had. To my surprise, the buzz disappeared with no loss
of signal strength.

(From: Dan Hicks (danhicks@millcomm.com)).

An even better idea is to put these chokes on the RF **generators** in 
your house.  I'm not sure if it's "code" to install them on permanent 
wiring, but it should be safe to do so so long as you are reasonably 
careful.  And it's easy to install them on any plug-in devices that appear
to cause problems.

  14.18) Internal fuse blew during lightning storm (or elephant hit power pole)

Power surges or nearby lightning strikes can destroy electronic equipment.
However, most of the time, damage is minimal or at least easily repaired.
With a direct hit, you may not recognize what is left of it!

Ideally, electronic equipment should be unplugged (both AC line and phone
line!) during electrical storms if possible.  Modern TVs, VCRs, microwave
ovens, and even stereo equipment is particularly susceptible to lightning and
surge damage because some parts of the circuitry are always alive and therefore
have a connection to the AC line.  Telephones, modems, and fax machine are
directly connected to the phone lines.  Better designs include filtering and
surge suppression components built in.  With a near-miss, the only thing that
may happen is for the internal fuse to blow or for the microcontroller to go
bonkers and just require power cycling.  There is no possible protection
against a direct strike.  However, devices with power switches that totally
break the line connection are more robust since it takes much more voltage
to jump the gap in the switch than to fry electronic parts.  Monitors and
TVs may also have their CRTs magnetized due to the electromagnetic fields
associated with a lightning strike - similar but on a smaller scale to
the EMP of a nuclear detonation.

Was the unit operating or on standby at the time?  If was switched
off using an actual power switch (not a logic pushbutton), then either
a component in front of the switch has blown, the surge was enough to
jump the gap between the switch contacts, or it was just a
coincidence (yeh, right).

If it was operating or on standby or has no actual power switch, then
a number of parts could be fried.

Many devices have their own internal surge protection devices like MOVs (Metal
Oxide Varistors) after the fuse.  So it is possible that all that is wrong is
that the line fuse has blown.  Remove the case (unplug it!) and start at
the line connector.  If you find a blown fuse, remove it and measure across
the in-board side of fuse holder and the other (should be the neutral) side
of the line.  With the power switch off, this reading should be very high.
With the switch on, it may be quite low if the unit uses a large power
transformer (a few ohms or less).  For example (assuming power transformer
operated supply):

        * Small AC adapter - 100 to 500 ohms.
        * Large AC adapter - 10 to 100 ohms.
        * VCR - 15 to 30 ohms.
        * Cassette deck or CD player - 25 to 100 ohms.
        * Stereo receiver or amplifier - .5 to 10 ohms.

Some may be outside these ranges but if the reading is extremely low, the
power transformer could have a partially or totally shorted primary.  If
it is very high (greater than 1 K ohms), then the primary of the power
transformer may be open or there may be blown thermal fuse under the outer
insulation wrappings of the transformer windings.  This may be replaceable.

If the unit has a switching power supply, see the document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies".

If the resistance checks out, replace the fuse and try powering the unit.
There will be 3 possibilities:
1. It will work fine, problem solved.

2. It will immediately blow the fuse.  This means there is at least one
   component shorted - possibilities include an MOV, line filter capacitor,
   transformer primary.

3. It will not work properly or still appear dead.  This could mean there are
   blown fuses or fusable resistors or other defective parts in the power
   supply or other circuitry.  In this case further testing will be needed
   and at some point you may require the schematic.

  14.19) Use of surge suppressors and line filters

Should you always use a surge suppressor outlet strip or line circuit?
Sure, it shouldn't hurt.  Just don't depend on these to provide protection
under all circumstances.  Some are better than others and the marketing
blurb is at best of little help in making an informed selection.  Product
literature - unless it is backed up by testing from a reputable lab - is
usually pretty useless and often confusing.

Line filters can also be useful if power in you area is noisy or prone
to spikes or dips.

However, keep in mind that most well designed electronic equipment
already includes both surge suppressors like MOVs as well as L-C
line filters.  More is not necessarily better but may move the point
of failure to a readily accessible outlet strip rather than the innards
of your equipment if damage occurs.

It is still best to unplug everything if the air raid sirens go off or
you see an elephant wearing thick glasses running through the neighborhood
(or an impending lightning storm).

  14.20) Surge Suppressor/UPS cascading

(From: Fred Noble (f-noble@suttondesigns.com)).

A large number of users still seem confused about the use of a Surge
Suppressor in line with a UPS. The general rule is, do NOT plug a surge
suppressor INTO the OUTPUT of a UPS that produces a non-sinewave output that
exceeds 5% Total Harmonic Distortion (or THD) when the UPS operates from
battery supporting any load under any ambient conditions.  Do NOT plug a Line
Conditioner or other type of filter into the UPS either.

You can plug a UPS into a well grounded surge suppressor, but this is not
always a good idea, especially when we are talking about various 'low cost'
surge suppressors of questionable electrical integrity.  We constantly hear of
low-end surge suppressor recalls for safety reasons, with several recent
recalls ordered by the U.S. Consumer Product Safety Commission, for example, http://cpsc.gov/cpscpub/prerel/prhtml97/97078.html.  A cursory search using
the keywords 'surge arrester consumer recalls' with the Excite engine reveals
several such recalls.

If the surge suppressor you plug the UPS *into* is electrically 'safe' you are
still extending the ground path with such a cascading arrangement, which, on
balance, may not be wise. The UPS should provide Surge Suppression energy
ratings of 480 Joules or more.  Then, you probably wouldn't require the
additional upstream surge suppressor at all. This does not mean that you
shouldn't also have a surge suppressor installed at the MAINS or the branch
panel, however.  We are only talking about the extra, stand-alone, AC
protection devices.

This is also not to say that you should not provide additional surge
suppression for your modem or UTP connections!. This you must do, and a low
cost device that is also a *high quality* device, should be used.  These
devices are designed specifically for the protection of DC electrical surges
and they are not used in series with a UPS anyway.

  14.21) Lightning, surge supressors, and telephone equipment

(From: aa-2@deltanet.com@deltanet.com)

Nothing will stop a good lightning strike, but there are things you can do
to put the odds more in your favor.

For telephone line protection, the place to start is where the phone line
comes into your house.  Locate the protector and verify you have a good
ground close to it.  Next, replace the standard carbon protector elements
with gas tubes.  These often look like large brass hex bolts with no wires
attached, but the exact design will vary.  Carbon protectors operate rather
slowly; gas tubes ionize very quickly and carry large amounts of current.
You may have to shop around your local telco supplier to find these.
Strictly speaking, these are on the telco side of the demarc and you're
not supposed to fool with them, but if you won't tell, I won't either.  Or
you could call your local telco and ask for the gas tubes...

Then add your store-bought protector inside.  Make sure it has a good
ground, too.  It can't hurt, and it might help.  But the best place to try
and stop the lightning is before it enters your house.

  14.22) Equipment dropped or abused

I have heard of someone fighting off a would-be mugger with a tape deck
but this is generally not a recommended practice.  However, once it
happens - your cassette deck fell off its shelf or you prized walkman
fell from your hang glider (ok, maybe that will be too much even for
miracles) - what should you do?

Overall, electronic equipment - especially portable devices - are quite
tough.  However, falling or being beaten in just the wrong way can do
substantial and possibly not immediately visible damage.

If you take it in for service, the estimate you get may make the national
debt look like pocket change in comparison.  Attempting to repair anything
that has been dropped is a very uncertain challenge - and since time is
money for a professional, spending an unknown amount of time on a single
repair is very risky.  There is no harm is getting an estimate (though
many shops charge for just agreeing that what you are holding was once
a - say - tapedeck!)

This doesn't mean you should not tackle it yourself.  There may be
nothing wrong or very minor problems that can easily be remedied.

First, unplug the unit even if it looks fine.  Until you do a thorough
internal inspection, there is no telling what may have been knocked
out of whack or broken.  Electrical parts may be shorting due to a broken
circuit board or one that has just popped free.  Don't be tempted
to apply power even if there are no obvious signs of damage - turning
it on may blow something due to a shorting circuit board.  If it is a
portable, remove the batteries.

Then, inspect the exterior for cracking, chipping, or dents.  In addition
to identifying cosmetic problems, this will help to locate possible areas to
check for internal damage once the covers are removed.

Next, remove the covers and check for mechanical problems like a bent or
deformed brackets, cracked plastic parts, and anything that may have
shifted position or jumped from its mountings.

Carefully straighten any bent metal parts.  Replace parts that were
knocked loose, glue and possibly reinforce cracked or broken plastic.
Plastics, in particular, are troublesome because most glues - even plastic
cement - do not work very well.  Using a splint (medical term) or sistering
(construction term) to reinforce a broken plastic part is often a good
idea.  Use multiple layers of Duco Cement or clear windshield sealer
and screws (sheetmetal or machine screws may be best depending on the
thickness and type of plastic).  Wood glue and Epoxy do not work well
on plastic.  Some brands of superglue, PVC pipe cement, or plastic hobby
cement may work depending on the type of plastic.

Cycle the the mechanism and check for free movement of the various
moving parts.

Inspect for any broken electronic components - these will need to be replaced.
Check for blown fuses - the initial impact may have shorted something
momentarily which then blew a fuse.

There is always a slight risk that the initial impact has already fried
electronic parts as a result of a momentary short or from broken circuit
traces and there will still be problems even after repairing the visible
damage and/or replacing the broken components.

Examine the circuit boards for any visible breaks or cracks.  These will
be especially likely at the corners where the stress may have been greatest.
If you find **any** cracks, no matter how small in the circuit board, you
will need to carefully inspect to determine if any circuit traces run
across these cracks.  If they do, then there are certainly breaks in
the circuitry which will need to be repaired.  Circuit boards in consumer
equipment are almost never more than two layers so repair is possible but
if any substantial number of traces are broken, it will take a great deal
of painstaking work to jumper across these traces with fine wire - you cannot
just run over them with solder as this will not last.  Use a fine tipped low
wattage soldering iron under a magnifying lens and run #28 to 30 gauge
insulated wires between convenient endpoints - these don't need to be directly
on either side of the break.  Double check each connection after soldering for
correct wiring and that there are no shorts before proceeding to the next.
Also see the section: "Repair of printed circuit board traces".

If the circuit board is beyond hope or you do not feel you would be able
to repair it in finite time, replacements may be available but their cost
is likely to be more than the equipment is worth.  Locating a junk unit of the
same model to cannibalize for parts may be a more realistic option.

Once all visible damage has been repaired and broken parts have been replaced,
power it up and see what happens.  Be prepared to pull the plug if there
are serious problems (billowing smoke would qualify).  Determine if it
appears to initialize correctly - without shutting down.  Play a garbage
tape to determine if there are any problems that might damage the tape.
Listen carefully for any evidence of poor tracking, tape speed instability,
or weak or muddy audio that might indicate that tape path alignment requires
further attention.  Listen as well for any unexpected mechanical sounds that
were not there before.

Very likely, the unit will be fine, you can replace the covers, and now find
a more secure spot for it to prevent this sort of event in the future.  Maybe
hang gliding is just not for you!

  14.23) Decayed glue in electronic equipment

Larger components like electrolytic capacitors are often secured to the
circuit board with some sort of adhesive.  Originally, it is white and
inert.  However, with heat and age, some types decay to a brown, conductive
and/or corrosive material which can cause all sorts of problems including
the creation of high leakage paths or dead shorts and eating away at nearby
wiring traces.

The bottom line: Most of the time, this stuff serves no essential purpose
anyhow and should be removed.  A non-corrosive RTV or hot-melt glue can be
used in its place if structural support is needed.

(From: Richard Rasker (r.e.rasker@student.utwente.nl)).

Are you repairing somewhat older Japanese (Yamaha, Nikko, etc.) equipment, but 
the problem seems very obscure? Then maybe this may interest you:

In some amplifiers and other equipment, the supply capacitors and other large 
pcb-mounted devices are secured in place by a type of gluelike substance, that 
after several years causes corrosion to all metal parts that it touches; 
eventually, the metal connections (like component wire leads and wire bridges) 
will fail.

The substance in question is a dark yellow rubber-like compound, coloring 
brown and turning rather hard on the places where damage is done to other 
components. The only solution is to scratch it away completely and replace all 
components affected.

I've already repaired five amps where this turned out to be the cause of 
trouble - with very vague symptoms, like a missing ground reference to an 
endstage, an on-board controller that wouldn't start up, etc. The first time
it took me forever to find, so if this posting will make even one repair
easier for someone, I'm already happy.

Hope this makes life a (little) bit easier for all those people out there 
trying to repair stuff, instead of throwing it away :)

P.S. My theory about this process: I think that the substance used is a rubber 
compound with an excess of sulfur, which will very slowly react with oxygen 
and moisture to form corroding chemicals (like sulfites). If anyone has a 
better theory (or the correct explanation), please let me know.

(From: Jake Gray (jake79@hotmail.com)).

I have found in a lot of electronical gear and more recently in my monitor.
The glue has been designed mainly to hold leads and wires in place, also to
hold capacitors in place.

It eventually soaks up the moisture from the air, giving it a conductive
effect and the places that it is located don't like having a conductor across
them.  And, as time goes on, the glue seems to carbonize and become an even
better conductor.

Just keep and eye out for it, it is like a creamy colour and remove it ASAP.

With many appliances, especially those with many IC's, I have found that with
the removal of the glue, they work fine.

  14.24) Repair of printed circuit board traces

In most cases, a functional repair - using wire to bridge the breaks soldered
to conveniently located pads - is all that is needed.  This will be at least
as reliable as the original foil wiring if done properly.  However, there are
those times when a complete restoration is desired:

Note: If the original cause was chemical corrosion rather than mechanical, ALL
of the offending material must be removed and/or neutralized before any sort
of reliable repair can be attempted!

(From: MKILGORE (mkilgore@aol.com)).

Yes, you can repair damaged/lifted conductors and pads on circuit boards. 
If you would like to repair the damaged area professionally, track repair
kits are available from sources such as Pace. These repairs once completed
are almost undistinguishable from the original work. Damaged pad
replacement -  Using a scalple or Xacto knife follow the run attached to
the pad back to a point where it is still firmly secured, at a 45 degree
angle, cut the trace loose and remove it from the board and discard.
Scrape any solder mask from the end of the trace back about 3 trace
widths, and clean the area with an ink eraser, then tin the area.  Select
a pad with trace from the kit ( various sizes are included ) position it
in place of the damaged run and form it so it follows the contour of the
board to the 45 degree angle cut and rests on top of the original trace by
about 2 trace widths.   Now prepare a small amount of two part epoxy and
flow it on the board where the replacement conductor will lie, do not get
any on the tinned conductor. Lay the replacement conductor in place and
allow the epoxy to dry, this can be speeded up with a heat  lamp. Once dry
simply apply flux to the joint and solder the two pieces together. If this
was a plated through hole, or strength is an issue, the kit contains eyelets
which can be installed through the board.  ---  However, if the trace you
wish to repair is merely lifted you can simply use the epoxy and secure it
back in place.

  14.25) Circuit repair where a pad has been lifted due to mechanical stress

This might be the case where someone tripped over the AC adapter cord of a
walkman or laptop computer thus ripping the jack from the circuit board.

(From: KIRTO (Kholson@cris.com)).

As you will see in the following, I recommend using something other than the
pad to get that strength.

I suggest you provide mechanical connection between the jack and the board so
that the jack can't move with respect to the board.

Techniques include a wire strap over the component near the back and soldered
to the board like you see on crystals or adhesive under the jack like you see
on large caps in midboard.

Another possibility is to put a rubber bumper atop the jack so that the front
cannot tip inward when it's in the case. A stick-on foot might be a start,
with whatever 'foot surgery' is needed to fit.

If the jack has a rim near the front (like a std keyboard connector) you might
be able to put triangular braces on either side of it with adhesive and some
stiff rubber or plastic.

I have seen this problem happen when someone trips on a cord and thus pulls
the connected jack at a sharp angle with high force. Warn the customer about
this possibility, and suggest using an extension cord on the power adaptor.

(From: Hank Sievers (textax@aol.com)).

The best way that I can think of is to bend down whatever part of the leg
extends through the board and bridge with a heavy bare wire and plenty of
solder to as much of the nearest part of the trace (scraped to the copper, of
course) as you can. Then, for good measure put a drop of magic glue or some
silcone sealant where the leg comes through the hole. Should be stronger than
the original.

I am a charter member of the the 'down-to-the-component-troubleshooting
fraternity', since I am naturally curious and fortunate enough to have the
time, since I am retired. However, I can see where it is often important to
the bottom money line, not to spend too much time on a repair and so replace
the entire unit. Time is money also!

  14.26) Boombox or other equipment went to the beach (sand and/or surf)

A (former) relative took your boombox to the beach this summer and now
it has sand or perhaps salt in it.  Or, maybe you could not resist
"sing'n in the rain" and a big bus went by without slowing.  Now neither
of the tape decks will play.  Can this possibly be fixed?  Will it be
worth the effort?

Unless this is a really expensive sophisticated unit, I doubt whether it
will pay you to take it anywhere for repair.  Furthermore, as with equipment
that has been dropped or physically abused, few repair shops will be inclined
to touch the job.  They really don't like challenges of this sort.

That leaves you!

If saltwater was involved in a significant way, you can probably forget it.
Without immediate attention, saltwater corrosion can set in very quickly and
attacks electronic components, circuit board traces, cable wiring, and 
mechanical parts.  The only thing worse is damage caused by forgotten,
leaky batteries.

Although it is probably too late, the first thing to do when electronic
equipment gets wet is to remove the power source - switch it off and
pull the plug or remove the batteries if possible.  Don't be tempted to
apply power until you have determined that it is completely dried out.
If power was on when the 'incident' took place, then electronic damage
may have already resulted which will not be apparent until after cleaning,
drying, and lubrication.

The following description assumes a dual cassette boombox.  Adjust
as appropriate for your patient:

If the tape decks are totally dead, you may have serious electronic or
corrosion which will make any salvage unlikely.  If they sort of move
(or even twitch a bit) but the sound is erratic, weak, fluttery,
etc. then there may be hope.  (Of course, if it got wet, you should not
have done this test until everything was cleaned and dried!)

NEVER use strong solvents for any cleaning.  These may attack plastic
parts or cause internal damage to electronic components.

Mechanical intensive care:

1. Remove the tape decks.  This will be a pain but otherwise you will not
   be able to get at everything.  Make as many as drawings as needed so
   you will be able to reassemble.

2. Make a drawing of the belt routing, remove the belt(s), wash and dry
   them, label and set them aside.

3. Use a soft brush (like a paintbrush) to dust out as much sand as possible.
   Hopefully, you can get it all this way.  A vacuum cleaner with a wand
   attachment may prove handy to suck out sand.  Don't use high pressure
   compressed air - it will just spread the sand around.  Any grease or oil
   on which sand has collected will need to be totally removed and replaced
   with fresh lubrication.

4. If there is evidence of salt (remember, I said forget it...but), you
   will need to wash it off.  Yes, wash it.  Keep water out of the
   motors.  Use low pressure compressed air (a blow dryer on low heat
   should be fine) to dry so that it does not rust.  Ditto if it is still wet
   with contaminated liquid (we won't say where this came from), wash with
   fresh water to remove all traces of it as quickly as possible.  A final
   rinse with 91% or pure isopropyl alcohol will decrease drying time
   and should not damage mechanical assemblies.  Degreaser may be used if it
   is safe for plastic and rubber parts.

   Lubricate all bearing points with a drop of light machine oil - electric
   motor oil, sewing machine oil, etc. (Never never never WD40).  Lubricate
   gears, cams, and sliding parts with a light plastic safe grease.

5. Replace the belts and reinstall the tape decks.

Electronic intensive care:

1. Remove the circuit boards and label the connectors if there is any
   possibility of getting them mixed up.  If the circuit board(s) are soldered
   to the rest of the equipment, then you will have to improvise.

2. Wash with water and dry thoroughly.  This does work.  I use it routinely
   for degunking remote controls and rubber membrane keypads, for example.
   The most important objective should be to get corrosive liquids off the
   components and circuit traces as quickly and completely as possible.  A
   final rinse with isopropyl alcohol will decrease drying time.  However,
   there is a slight risk of damage to sensitive electronic components should
   some be trapped inside.  Moisture will be trapped in controls, coils,
   selector switches, relays, transformer cores, connectors, and under large
   components like ICs.  Pat dry, then use warm air from a hair dryer (or
   heat gun on low) to completely dry every nook and cranny.  DO NOT operate
   until everything inside and out is thoroughly dry.

3. Inspect for damage due to short circuits including blown fuses, fried
   components, and melted traces.  These will need to be repaired or

4. Use spray contact cleaner on the switches and control cleaner on the
   user controls and adjustment pots.  DO NOT turn the internal adjustments
   without precisely marking the original positions - else realignment will
   be needed.  Exercise the user controls to help the cleaning process.

Once everything is reassembled, power the unit up and see what happens.  Be
prepared to pull the plug or pop the batteries if there are serious problems.
Attempt to play a garbage tape to determine if there are any problems that
might damage the tape.  Look and listen for any abnormalities which may
require additional attention.  There could still be electronic faults
not repairable without schematics and test equipment.

Obviously, this description is very simplistic.  The important thing is
to get every last grain of sand, salt, and other contaminants off of the
mechanisms quickly.

Similar comments apply to equipment that went for an actual swim - you
dropped your portable CD player in the toilet.  The most important objective
is to clean and dry it as quickly as possible and then relube any motor
and other bearings.  Use your judgement as to the severity of the dunking
in terms of how deeply the liquid penetrated.  Surface moisture will not
hurt anything as long as it is dried up quickly.  If you left it soaking
on the other hand....

As noted above, moisture may collect inside certain electronic parts and
it is essential that these be dried completely before attempting to apply
power to the unit.  If you do not, at best it will not work properly and
you may do additional serious damage due to short circuits.

For the mechanics, the same applies though this is trickier since certain
parts need to be lubricated and these may not be readily accessible or
obvious.  Don't be tempted to overdo the lubrication either - too much is
worse that too little.

For high tech devices like CD players, some parts of the internal optics
or shielded DC-DC convertors may be impossible to access and clean of scum.

  14.27) Salt water salvage

(From: John Baker (jbaker@flash.net)).

I have repaired equipment that has been soaked in salt water and it depends
on what type of components it has on the boards. If they have any batteries
on them, get them off as soon as possible. transformers are usually good for
rusty paperweights. Get the boards out of the salt water and into fresh water
ASAP. I have not found any chemicals that will remove the salt deposits and
leave the traces. The best bet is to use a small nylon brush along with a
chemical called Flux Off-nr, there are several types of Flux-Off, get the
one  that does not harm plastic parts, it is not as strong but it workes
just as well in this case. From there it takes a lot of time. Use the brush
and remove all salt deposits, try and get under all components, especially
IC's. Most components can take being under salt water with no damage, it is
the batteries and metal that cause problems.

  14.28) Fil's notes on rescuing soggy equipment

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

Greetings. I've recently had the opportunity to rescue several rather
expensive electronic units after the owner flipped the canoe and spilled
the beans, so to speak. 

The dead units were: a Casio solar-powered calculator, a car-alarm key ring
transmitter, a 10-satellite GPS unit (yowser!), and some smaller items.

Note: GPS unit was waterproofed and did not suffer much.

Solution (sorry, pun) was: purchase 1 gallon of distilled water, disassemble
the units and submerge the PCBs (and keypads and displays) in containers. The
devices were left soaking for more than 20 minutes. Then, they were removed
and dried with a hair dryer (and fan for less expensive items).

Results: excellent. All items have been brought back to life. Some *did*
require purchase of new (rather expensive) Lithium batteries but that was
a small price to pay. 

Hint: It is highly useful to have a brush to clean the area between ICs' pins
after 10+ minutes of soaking. This helps to remove any minerals that are not
as soluble in water as others. This is more of an issue if the items came in
contact with flood-stage stream than a sinkful of tap water. :-)

Observation: devices that were "on" at the time of the dunking were the most
damaged and required the most time to soak. Batteries had to be replaced since
they *all& started to leak.

  14.29) Reviving old (antique) equipment

If you have a true antique - really old, and valuable, you should refer
to the extensive literature available on this subject.  The following
applies more to that 30 year old record player/amp found in the storage loft
of your garage during spring cleaning.

Common problems relate to two types of components: vacuum tubes (valves
for all of you on the other side of the lake) and capacitors (paper and
electrolytic type).  Push all the tubes down in their sockets as well - they
will work their way loose with non-use and vibration.  However, thorough
cleaning of all socket and switch contacts, and controls will almost certainly
be needed.

Warning: the voltages inside tube type equipment can exceed 400 V - and
contact with that can be real painful not to say dangerous.  AC-DC type
sets are not isolated from the power line.  (In some really old equipment,
even the chassis may be tied to one side of the line).  This could also
happen as a result of a shorted component.  The electrolytic capacitors
can hold a charge for quite a while.  Read, understand, and follow the
recommendations in the document: "Safety Guidelines for High Voltage and/or Line Powered Equipment".  Use extreme care when probing or even touching
anything.  This isn't 5 V logic!

Vacuum tubes:

It is not possible to fully test vacuum tubes without proper equipment
but the inspection and tests below will find most bad tubes but will not
pick up weak tubes.  As a side note, when a repair shop replaced tubes,
perhaps 20 % of the tubes they replaced were actually bad (I know because
the local TV repair shop's trash can was a favorite hangout on pickup day
and nearly all the tubes I scrounged tested perfectly good on a real tube
tester once they were washed of coffee grounds and cigarette ash!)  Whether
this represented legitimate preventive maintenance or just IPM - Increased
Profit Margin, I really do not know.)

1. Look for a silvery metallic spot somewhere inside the tube.  This is the
   getter and is there to remove the last traces of gasses.  If you see this,
   the vacuum is intact.  If it is milky white or red, the tube has lost its
   vacuum and is dead-dead.

2. Use an ohmmeter to test for filament continuity.  The nice thing about
   tubes (aside from their cheery glow) is that you can see inside (at least
   for the ones with a glass envelope) and locate the filament connections by
   tracing from the pins - it will be the whitish fine wire in the center of
   each of the tube sections.  (The filament is almost always pins 3 & 4 on
   a 7 pin tube, 4 & 5 on a 9 pin tube, and 2 & 7 on an 8 pin tube.)

3. You can check for inter-element shorts (but not at normal operating
   conditions) with a VOM or DMM.  For glass tubes, even without a tube manual,
   you should be able to deduce which elements are supposed to be isolated
   by visual examination.

Now, just jump into your time machine, back about 20-30 years should do it
(remember?) when every corner drugstore and TV repair shop had a tube tester.
There is, of course a good chance that your local TV repair shop still has
one (if they can find it under an inch layer of dust) and it may even work.

Capacitors and resistors:

If you just dug this thing out of the attic, it is very likely that
electrolytic capacitors have dried up and paper capacitors have turned
leaky.  Professional restorers will often install modern replacements
for all of these capacitors without even testing the old ones.  To maintain
the authenticity of the vintage equipment, they may actually remove the guts
of the old capacitors and mount the new ones (which are much smaller anyhow)
inside the original cans.

Old carbon resistors can absorb moisture and change value.  If your
measurements do not agree with their marked rating based on their
tolerance, consider replacements.  However, if within, say, 20 %, for
now, leave them alone.

Sockets, switches, and controls:

Vacuum and/or use a small paintbrush to remove dust, spider webs, dead
insects (and anything larger).

Use contact cleaner on all the tube sockets and selector switches.  Use
control cleaner on all the potentiometers and reostats.  Apply a drop of
oil to any variable capacitor bearings and mechanical dial pointers.

Testing (use an isolation transformer with AC-DC line connected sets):

Much of this old equipment had schematic diagrams pasted to the cover - really
handy if the paper hasn't totally disintegrated.

Turn on the power but be prepared to pull the plug in a hurry if, for example,
a capacitor should decide to blow up (this shouldn't be a problem if you
replaced them all unless some electrolytics are in backwards).

It is probably best to use a Variac to increase the voltage gradually.  In
fact, this will help to 'reform' old electrolytic capacitors that have
developed excessive leakage.  However, by 'gradually', we may be talking hours
or days to reform capacitors!  I would still recommend replacement even if
this appears to work.

Do the filaments light up?  If your equipment has a power transformer,
the filaments are probably wired in parallel, so if one tube is out, that
tube is bad (or its socket).  If they are all out, then the power
transformer or AC line input is bad.

If it is an AC-DC set like a table radio, then the tube filaments are
wired in series.  If one is bad, they will all be out.   Get out your
ohmmeter, pull each tube, and check it for filament continuity.

Assuming the filaments check out - all sections glowing (for metal tubes,
feel the case for warmth after a few minutes though this won't guarantee
that all sections are alive) when power is applied:

WARNING: It is possible for metal cased tubes to develop a short between one
of the high voltage electrodes like the plate and the metal case.  Test with
a voltmeter before grabbing one of these and keep that other hand in your back

Check for DC voltages out of the power supply.  There will be big filter
capacitors - check across those.  Watch out: we are talking several hundred
volts and BIG capacitors - ouch.

With no signal, check plate voltages on the various stages - there should 
something.  If you measure 0, then a plate resistor or coil could be open
or the tube may be shorted.

The rest is just basic troubleshooting.  Think of the vacuum tubes as oversize
high voltage depletion mode FETs (field effect tubes, why not?).  This is
not much different than modern equipment except for the bites the relatively
high voltages can take out of your hide.

  14.30) Additional comments on old equipment restoration

(From: Carl Ratner (artdeco@bway.net)).

A good place to post problems is rec.antiques.radio+phono. There are often
discussions there about fixing vintage electronic gear.

Many long books have been written about fixing old radios! If you don't want 
to do a lot of reading and learn a lot of theory, here are some practical tips: 
First, give the radio a thorough physical inspection with the power 
disconnected. Use your eyes and your nose. Look carefully for broken or 
disconnected wires, charred components, damaged insulation, etc. If you see 
wax dripping from a transformer or if it smells burnt, there has been an 
overload of some sort that will need to be identified. If the set has an 
internal antenna, make sure that it is connected. If an external antenna is 
required, connect a long piece of insulated wire, say 15 feet,  and lay it on 
the floor. Old sets will play very weakly or not at all if the antenna is 
missing. Always replace the power cord if it is deteriorated. 

In radios of 1930s vintage, it's very likely that all wax paper capacitors, as 
well as the electrolytic capacitors, are bad. First thing to do is replace 
all the wax paper ones with modern mylar types. If you have the tall metal can 
electrolytics, you can put modern ones under the chassis (the new ones are 
tiny). However, you must disconnect the old ones from the circuit... don't 
bridge the new ones across the old. Be sure to observe polarity of 
electrolytics. You may leave the old cans in place to retain original 
appearance. BTW, the old square mica capacitors seldom need to be replaced 
unless the cases are cracked open of they have other obvious damage.

Even if some of the old wax paper capacitors are still good, they are likely 
to fail within a few days if you start using the set. I've restored hundreds 
of old radios and have learned this from experience. Get them all out of 
there and save yourself a lot of trouble.

You should also check the value of all the carbon resistors in the set. They 
tend to go high or open with age. Replace the bad ones with modern equivalents 
(same resistance and wattage). You may have to disconnect one side of a 
resistor when testing it, as the associated circuitry can cause a low reading.
However, if a resistor reads way too high, you don't have to bother 
disconnecting it for testing as it is definitely bad.

Your set should start playing quite well after you change all the capacitors 
and possibly some resistors. You noted that you had changed the tubes, and 
I'll assume that all the replacements are good. Tubes don't fail nearly as 
often as people would expect, however, and it's possible that the set's 
original tubes were OK. Once you get the set working, you can substitute the 
old tubes one at a time to see if the set continues to play. Then just keep 
the good ones as spares.

Set still dead? If you have a multimeter, check the B+ voltage. The 
audio output tube's plate connection is a good place to do this. This can be 
250-350 hundred volts in a transformer set, so work with care. If B+ is absent 
or some very low value, you have a problem in the power supply. (If you tell 
me the tube numbers in your set, I can give you some of the pinouts for 
testing) If the rectifier tube is known to be good, and you have already 
changed the electrolytics, then you may have a bad power transformer (large 
black box, usually near a back corner of the chassis. These are hard to find 
nowadays and very costly. I'm assuming here that you don't have a B+ short 
somewhere else in the radio. You will know about that because something will 
be smoking if such a short exists!

There are other components that can fail. Inspect the speaker for physical 
damage. You can test the voice coil and field coil for continuity. Replace 
if open. A modern permanent magnet speaker can be substituted for an old 
field coil speaker, but a power resistor of abut 1500 ohms, 20 watts 
must be added to replace the field coil. Dirty volume controls and band 
switches can cause noisy, weak or intermittent sound too. Clean them with a 
good spray cleaner such as Deoxit D5. Avoid the "tuner cleaner" that 
is sold at Radio Shack. It is worthless for fixing old radios.

As a final step, your set may need an alignment. This consists of adjusting 
all the tuned circuits to factory specifications to obtain the best possible 
performance from your set. You need a signal generator and an output meter to 
do this properly. It is strongly recommended that you do not twiddle any 
screwdriver adjustments on the IF transformer cans or elsewhere in the set 
unless you know exactly what you are doing. Misadjustment will cause the set 
to play very poorly or not at all.

End of short course in fixing old radios.

(From: R.G. Keen (keen@eden.com)).

1. Use a battery or ohmmeter to verify that the speaker clicks when 
   electricity hits it.

2. Disconnect the output transformer primary and use the battery on the 
   primary to verify that it makes the speaker click, albeit faintly.

3. Power the amp. verify that the plate(s) on the output tube(s) are sitting
   slightly below B+, and that cathode is near ground, grid more negative than

4. Touch a probe to the grid of the output tube, listen for a click in the
   speaker. No click means that the output tube or it's surrounding circuitry
   is bad.

5. Assuming that (4) worked, go one tube back up the signal chain at a time,
   touching grids and listening for clicks. When the clicks stop, that tube or
   the circuitry around it is bad.

6. When you find the bad one(s), measure all the resistors and check the
   capacitors for leakage. Measure the tube pin voltages for plate high,
   cathode low and grid less than cathode. sub in a new tube.

7. It could be an open volume or tone pot between stages. Also a bad solder
   joint. remelt and touch with a bit of rosin core solder every joint in the
   bad stage. 

(From: John Mitchell (j.b.mitchell@qmw.ac.uk)).

Get a hold of the "The Amp Book" (or something like that) by Aspen Pittman.
It's stuffed full of dozens and dozens of tube amp schematics plus other info
on mods servicing etc.

  14.31) Tube amp web sites

Tube amp FAQ:

* http://www.eden.com/~keen/tubeampfaq/tube_amp.htm

Sites with tube amp design, troubleshooting, info, links:

(From: Duncan Munro (postmaster@muffy.demon.co.uk)).

* http://www.duncanamps.simplenet.com/
* http://www.triodeel.com

(From: Jan B. Jensen (jbj@lif.dk)).

* http://www.foundmark.com/ComJute/RealMcCoy.html
* http://venus.aros.net/~tboy/ampage/schems/twdpwr100.gif
* http://mirinae.yonsei.ac.kr/~hscheon/tube/
* http://nanaimo.ark.com/~pat/index.htm
* http://www.eden.com/~keen/
* http://www2.aros.net/~koda/htac/
* http://www.geocities.com/TimesSquare/1965/music_etc.html
* http://www.phy.ohiou.edu/~cigna/amps/

  14.32) TV/VCR combos

These hybrids which include both a TV and VCR (and sometimes other stuff
as well) seem to combine the worst of all possibilities.  Although, in
principle, the idea of a combination TV/VCR sounds good - no cabling to
worry about, ease of use, compatibility assured, the result may be less
than meets the eye.  While TV/VCR combo units do include both a TV screen
and a VCR transport, very often there is only a single shared tuner so
that viewing and recording of different programs is not possible unless
one is from an external baseband video source (assuming there is a suitable
input jack) like - you guessed it - a VCR or laserdisc player.

If either the TV or VCR poops out and needs repair, the entire unit may be
unusable either because of shared circuitry or because the whole thing is
in the shop.  Construction quality tends to be shoddy and some designs are
poor to begin with.  Finally, as if this is not enough, servicing is difficult
and painful because everything is crammed into a single compact (at least that
is a good feature!) unit.

Refer to the appropriate documents for your particular problems:

* TVs - "Notes on the Troubleshooting and Repair of Television Sets".

* VCRs - "Notes on the Troubleshooting and Repair of Video Cassette Recorders".

* Power supplies - "Notes on the Troubleshooting and Repair of Audio Equipment and other Miscellaneous Stuff".

  14.33) Boomboxes and compact stereo systems

These combine a stereo receiver and a single or dual cassette deck, and/or
a CD player or changer, and a pair of detachable speakers, into a single
unit.  Most are fairly portable but larger boomboxes and compact stereos
may require a forklift to move any great distance.

While the individual subsystems - CD player for example - are usually
relatively self contained electrically except for a common power supply,
mechanically, everything tends to be jumbled together - even on units
that have an outward appearance of separate components.  Both cassette
transports are usually driven from a single motor.  Getting at the CD
player may require removal of both cassette decks, audio amplifier, and
power supply.  Working on these is not fun.  As usual, take careful notes
as you disassemble the unit and expect it to require some time just to get
to what you are after.  Be especially careful when removing and replacing
the individual modules if printed flex cables are used for interconnections.

Refer to the relevant sections on cassette transports, loudspeakers, and
power supplies for problems with these units.  Refer to the document: "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives"
for CD specific problems.

Since these do get abused - bumped, dropped, dunked, etc., bad connections,
and other damage is very common.  See the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".

  14.34) Design to discourage repair

Here is a description of the pain involved in attempting to get at the
CD player part of a Garrard boombox.  Sadly, this is all too typical
of 'Getto Blaster' construction.

(From: BELJAN E (lvpy67c@ix.netcom.com)).

I managed to get the whole Garrard mess disassembled (this thing is a major
pain to service). The CD mechanism is removable, but just try it.  This
boombox has all sorts of modules: main board, display, cassette, radio, power
supply, and CD are all separate.  The problem is the way it is designed you
simply cannot reach all the connectors to get the CD player out. If I could
get the CD player out, I could disassemble it and find the solution. By the
way, voltage to CD section appears OK. I would not have been able to find
loose connections had there been any. I put it back together, CD still dead,
everything else still works.  It is convenient to service only if you intend
on replacing the entire mechanisms (possibly Garrard's motive?).  If I really
needed to, I could simply detach the CD mechanism and replace it. I wouldn't
bother.  I see they now have Garrard Boombox with Dual CD players, and one with
all sorts of features, one with detachable speakers and so on. This is a
mystery, with the voltages OK, it would seem that there would be a loose
connection, but none are visible (remember I cannot get the whole thing out).

I say this thing is a pain to service, here is why:

1. You must have an 8 inch long thin phillips screwdriver to disassemble it.

2. You must remove the cassette player to reach the Display.

3. You must remove the display to reach the switches.

4. You must remove the switches to reach the CD mechanism.

   An interesting note: the display modules are connected to the CD mech,
   along with the headphone module, they work fine.

5. you must unscrew the CD player from behind, then attempt to slide it
   forward, while it is connected to the main board from behind with white
   push on connectors. You get it halfway out, careful now, you don't want
   to damage the Cassette deck, which is connected somewhere out of visibility.

6. Once you slide it forward, you must try to loosen the slide on
   connectors without dropping the whole mechanism on the main board. (you
   need 6 hands and screwdrivers to try to do this. 

7. On top of all that, the Whole Front of the unit is hanging there, connected
   also out of site

This unit is incredible. Truly incredible. It is easy to replace whole
components, but servicing?

  14.35) Panel lamps out

In the old days, this was due to the failure of easily replaceable and
widely available miniature incandescent lamps.  Even today, may displays
are not LEDs as you might think but LCDs with backlighting provided by -
you guessed it - incandescent lamps.  Unfortunately, they are rarely
easily replaceable and or as widely available.

This will be particularly likely if the display color is anything but the
most common for LEDs - red.  You might find green LEDs but will not likely
find orange and certainly not blue or purple.  LEDs would not be orange
because the additional cost of orange LEDs would not translate into
increased sales of boomboxes (or whatever).  Blue LEDs are very expensive
and purple ones do not exist.

The bulbs are replaceable.  Getting at them may be easy or require entirely
disassembling the unit.  Soldering may be required as the manufacturer saved
a nickel by not providing a socket.  They may be tiny and special - try
places like MCM Electronics for replacements.

If they are really red LEDs or vacuum fluorescent displays, then the most
likely problem is a bad connection or other physical damage.

  14.36) Adjusting station/channel settings on tuning dials

So 95.7 MHz comes in a 100.1 MHz on the dial.

Don't touch any of the trimmers on the tuning capacitor!  They didn't magically
change their settings.  Just move the pointer on the dial cord to match a known
centrally located station.  If it is glued, you may have to carefully break
the bond between the pointer and the dial cord.  Then put a drop of household
cement to fix its position when you are satisfied with the adjustment.  Only
if the ends of the dial are way off frequency should you consider anything
beyond this mechanical fix.

Caution:  Be careful!  Should you accidentally cut the dial cord or have it
pop off of the pulleys, you will have a much bigger job ahead of you.  In 
this unfortunate circumstance, see the section: "Repairing a broken dial cord or tuning gang wire".

  14.37) Repairing a broken dial cord or tuning gang wire

With age, use, or through some mishap, it is inevitable: your analog dial
no longer works because the string that runs between the tuning knob, variable
capacitor, and dial indicator has broken.  How does one repair it?

The simple answer is: very carefully! :-)

These are a royal pain - especially if you do not know the original routing.
In this case, some of it is going to be by trial and error.  Some of my
learned-the-hard-way tips:

1. Major electronics distributors will actually be able to supply dial cord
   material without making too much of a face though they may have to go into
   a dusty old bin to locate it!

2. Start at the variable capacitor pulley.  Tie your favorite knot and secure
   it with some semi-flexible adhesive like Duco Cement(tm) or windshield

3. Route the cord around the appropriate idlers and the tuning knob shaft.

4. As a default, 3 turns on the tuning knob shaft seems to be common.  If
   there isn't enough space for 3 turns, use 2 turns.  If it slips with 3
   turns, use 4 turns.

5. If in doubt about the direction, determine which way it will end up turning
   the variable capacitor.  Clockwise rotation of the tuning knob should
   increase the channel frequency by decreasing the capacitance - plates

6. Use bits of electrical tape or putty to keep the cord from popping off
   of the idlers, etc., until you have it firmly attached to the spring
   on the other side of the variable capacitor pulley.

7. Once you are happy with the routing, pull it tight enough to stretch
   the tensioning spring about half-way.  With the cord held in place with
   your finger, confirm free and smooth movement throughout the entire tuning

8. Tie the cord off and seal it as in (1) above.

9. Install the dial pointer - it usually just clips on.  Tune a known station
   and slide the pointer along until it lines up with the correct frequency.
   Use a dab of sealer to keep it from wandering off.

Congratulations!  You are done.  Hopefully, only 3 or 4 iterations were
needed.  Now, if you need to do this again, it will be easier!  And, your
supply of tuning cord will probably last centuries.

One more gotcha: Don't attempt to solder circuitry near a dial cord - get
your iron near it and the stuff often used melts instantly - much fun!  Push
it out of the way or shield it with something.

  14.38) Revival of dead or tired remote control units

There are two types of problems with hand held remote controls: they
have legs of their own and they get abused or forgotten.  I cannot
help you with walking remotes.

Where response is intermittent or the reliable operating distance is
reduced, first check the batteries and battery contacts.  If some buttons
are intermittent or dead, than the most likely cause is dirty or worn
contacts under the rubber buttons or on the circuit board.

If there is no response to any functions by the TV or VCR, verify that any
mode switches are set correctly (on both the remote and the TV or VCR).
Unplug the TV or VCR for 30 seconds (not just power off, unplug).  This
sometimes resets a microcontroller that may have been confused by a
power surge.  Confirm that the remote has not accidentally been set to
an incorrect mode (VCR instead of TV, for example).  If it a universal
type, it may have lost its programming - reset it.  Make sure you are
using the proper remote if have multiple similar models.

Test the remote with an IR detector.  An IR detector card can be purchased
for about $6.  Alternatively, construct the IR detector circuit described
in the companion document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls".

If the remote is putting out an IR signal, then the remote or the TV or VCR may
have forgotten its settings or the problem may be in the TV or VCR and not
the hand unit.  The following is just a summary - more detailed information
is available in the companion document: "Notes on the Troubleshooting and Repair of Hand Held Remote Controls".

Problems with remote hand units:

All except (1) and (2) require disassembly - there may be a screw or two and
then the case will simply 'crack' in half by gently prying with a knife or
screwdriver.  Look for hidden snap interlocks.

1.  Dead batteries - solution obvious.

2.  Corroded battery contacts,   Thoroughly remove chemical deposits. Clean
    contacts with pencil eraser and/or sandpaper or nailfile.

3.  Broken connections often between battery contacts and circuit board,
    possibly on the circuit board - resolder.

4.  Bad resonator or crystal - replace, but diagnosing this without
    an oscilloscope may be tough.  Broken connections on resonator legs
    are common.

5.  Dirt/spills/gunk preventing keys from operating reliably.  Disassemble
    and wash rubber membrane and circuit board with water and mild detergent
    and/or then alcohol - dry completely.

6.  Worn or corroded contact pads on circuit board.  Clean and then use
    conductive Epoxy or paint or metal foil to restore.

7.  Worn or dirty pads on rubber keypad.  Clean.  If worn, use conductive
    paint or metal foil to restore.

8.  Cracked circuit board - can usually be repaired as these are usually single
    sided with big traces.  Scrape off insulating coating and jumper breaks
    with fine wire and solder.

9.  Bad LED. If IR tester shows no output, remove LED and power it from
    a 9V battery in series with a 500 ohm resistor.  If still no output,
    replace with readily available high power IR LED.  Otherwise, check
    driver circuits.

10. Bad IC - if it is a custom chip, forget it!  Failure of the IC
    is usually quite unlikely.

   (The following is from Duane P Mantick:)

   An awful lot of IR remotes use IC's from the same or similar series. A
   common series comes from NEC and is the uPD1986C which, incidentally is
   called out in the NTE replacements book as an NTE1758. A lot of these
   chips are cheap and not too difficult to find, and are made in
   easy-to-work-with 14 or 16 pin DIP packages. Unless you have no soldering
   or desoldering skills, replacement isn't difficult.

There are a large variety of universal remotes available from $10-$100. For
general TV/VCR/cable use, the $10 variety are fine. However, the preprogrammed
variety will not provide special functions like programming of a TV or VCR.
Don't even think about going to the original manufacturer - they will charge
an arm and a leg (or more). However, places like MCM Electronics do stock a
variety of original remotes - prices range from $9 - $143 (Wow $143, for just
a stupid remote! It doesn't even have high definition sound or anything
exotic). The average price is around $40.

  14.39) Problems with keypads or touchpanels

Most common are moisture problems followed by physical damage:

Very often, a little overzealous cleaning results in moisture trapped inside
a not quite perfectly sealed membrane keypad or touchpanel.

First, of course, dry off the exterior as best you can.  Any moisture
that seeped inside may be difficult to remove without surgery - which is
definitely not something you want to undertake as the long term reliability
will be compromised.

I would recommend waiting a while - a week may be required - for it
to totally dry out.  You could also try confirming across the touchpad
contacts with an ohmmeter that there is still low resistance (even 10s of
K ohms may look like a button press).  It is nearly impossible to speed
up this process without subjecting the device to conditions that may
harm the device - heat and/or vacuum.  You possibly try something like
isopropyl alcohol in the hope that it will displace the water and dry
quickly.  I do not know if this will be safe in every situation, however.

Of course, it is also possible that are other problems but I have seen
these things take a very long time to dry out.

However, significant damage - a membrane type touchpad is punctured - may
require replacement unless you can repair the internal wiring.  The
connections are usually made with flex-cables which are difficult or
impossible to repair.  See the section: "Repairing flexible printed cables".  Damage to any membrane buttons may result in stuck buttons
or improper operation of other buttons.

  14.40) Repairing flexible printed cables

It seems that more and more consumer devices from pocket cameras to
laptop computers are being built with miniature multiconductor flexible
printed cables.  Very often one or more traces to develop hairline cracks
due to repeated flexing.  In addition, damage from moving circuit boards
and modules during servicing is all to common.

Needless to say, repairing any kind of flex cable is a real pain!

Caution: many devices like calculators have printed cables that use
a material that will not take solder and are glued rather than soldered
at their ends - the logic board and LCD panel, for example.  Repair of
problems with the cables is virtually impossible.  Take great care when
working inside of devices with this sort of cabling to prevent damage
to the cables or their termination.

With types like these in particular where soldering is not possible at all,
the use of conductive paint, conductive Epoxy, or the stuff in a windshield
defrost heater repair kit are worth trying.

For the metallic conductor types, I have succeeded by carefully scraping the
plastic off with an Xacto knife and then soldering fine wire (#30 gauge wire
wrap for example) to the traces.  This presumes that the conductors on your
cable will even take solder.  I then cover up the joints with a flexible
sealer for electrical and mechanical protection.

However, you need to make sure that the wire you use can be flexed or that the
joint is set up in such a way that the wire does not flex much - else
you will just end up with broken wires pretty quickly.

Soldering from end point to end point if possible may be preferable.
Even going to only one endpoint would reduce the risk of immediate damage
and reliability problems in the future.

With multiple traces broken or damaged, you are probably better off replacing
the cable entirely.

(From: Steinar Botten (sbo@nera.no)).

I just fixed an electronic kitchen scale where the glued-on flex cable had
begun to come loose from the LCD display, causing some of the segments to
grow faint and disappear, while others showed when they shouldn't.  In my
first attempts I used conductive paint, but I couldn't get the viscosity
right so that the paint didn't spread and short-circuit some of the
connections.  So I removed and discarded the flex cable and cleaned the
tracks on the PCB where the cable had been attached.  I searched through my
collection of IC sockets and found one type with "fork-type" contact
springs that could be removed from the socket and that fit snugly over the
glass edge of the display.  The spacing of the contact points of the
display left just enough room for insulation (I used linen thread because
the subsequent soldering would have melted plastic tape) between the
contact springs.  After having fixed the display back on the PCB with
double-sided tape I soldered fine copper wire between the springs and the
PCB. And voila, the display was OK again.

Some ASCII art might make things clearer, here is a side view of the LCD
          ! ! !
          ! ! !
          ! ! !
  contact !_! !
  side --> ! !
          !! !!
          !___! <-- contact spring from IC socket

Obviously, this probably wouldn't work on a pocket calculator because of
the size of the contact springs.

  14.41) Comments on soldered flex cables

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

These are the leading cause of problems for me!  I repair camcorders for a
living, and all too often have seen these flex cables fall off the PCB, or are
so delicate in construction that they fall away from the PCB.

In many cases during repair stage, I often touch up the soldering with a low
heat iron, while pressing down on the soldered to PCB area of the cable, with
a flat plastic blade, enough to re-flow the connection. Then I take and apply
some general purpose glue around the cable to get it to adhere better to the
PCB and prevent tearing. Of course the consumer never should encounter a
problem unless the camcorder is dropped, and the case splits open and rips
the connectors away from the PCB.

Sony is infamous for having connectors fall off the boards.  Many brands of
camcorders are infamous for having connectors that mate 2 boards together
break away from the PCB.  It is a very bad situation because the boards they
work with are very expensive to replace. For the cost of a simple piece of
flex cable and 2 insertion force sockets, it is amazing they are cheap and
choose to mate the boards together directly, knowing that failure is just
around the corner!

Most commonly the CCD board or camera assembly is mated to the video (main)
PCB in this fashion and it is very sad when they break due to stress.  This is
one reason that the consumer should never ever attempt to repair delicate
items like this.

The best you can hope for in dealing with these is to never attempt to repair
the flex cable by soldering to it, etc. That is asking for future problems at

Don't 'tin' the ends of the cable either, you simply melt and distort it so
that it will no longer get a good connection into the socket.  Only clean it
possibly with denatured alcohol if needed - otherwise replace it.

Also do not stress them, you soon discover how easily they rip!

  14.42) About elastomer ('zebra stripe') connectors

Remember that first (or last) digital watch you took apart?  Remember how a
little piece of rubber fell on the shag carpet and you thought: "What the heck,
that can't be anything important".  Remember how the watch's display never
worked again?  Well, you lost the connector that linked the LCD panel to the
logic board.

Elastomer or 'zebra stripe' connectors are used to attach LCD panels to the
logic board and interconnect multiple boards on digital watches, calculators,
pocket computers, and many other modern gizmos.  It seems as if every cheap
and many not so cheap gadgets now uses this connector technology.

They can shift position, become dirty, and lose pressure due to warpage or
damage to the plastic retainers.  Very often, a weak display or missing
segments can be traced to a problem with these 'zebra stripe' connectors.
Equally often, disassembling, cleaning all parts with alcohol, drying, and
reassembling will return the device to (better than) new condition.  When
installing, make sure the striped edges are against the circuit traces if
there is any ambiguity.

Of course, it isn't that the zebra stripe shifts position a small amount - by
its nature this should not matter.  However, if the display shifts with
respect to the circuit board contacts or the zebra stripe material becomes
twisted or angled, poor and/or erratic connections will result.

(From: Spehro Pefhany (speff@gold.interlog.com)).

These are conductive elastomer connectors made from alternating layers of 
conductive (carbon filled) and insulating silicone rubber. 

There are also lower resistance versions with embedded wires, but they 
are not used for LCD displays because the series resistance doesn't matter 
for LCD's. 

Alignment to the PCB is critical as is even pressure, so they tend to be 
used only in high volume applications where a metal stamping or plastic 
molding is used to hold all the parts in place. 

  14.43) Identifying wiring on an auto radio/cassette

So you want to use your old car stereo as a boombox but don't have the
connection information.  Here is what I would do:

Locate the power - there will be a +12 switched and possibly a +12 unswitched
for channel memory.  At least one may be obvious if has an in-line fuse.  Use
an ohmmeter if necessary.  Once you have found the power connections, power it
from your 12 V power supply.  Keep the volume way down and use the balance and
fader controls to identify the speaker connections.  There will be either 2
pairs of wires or more likely 4 pairs for front and rear speakers.

  14.44) Ray's notes on plastic part repair

(From: Raymond Carlsen (rrcc@u.washington.edu)).

I recently had to repair a power supply for a camcorder. It was
dropped. Parts of the case were broken, and the circuit board inside was
cracked. Board repair was easy. I glued the PC back together with
superglue and soldered across the broken traces with jumper wires.

The plastic case presented me with more of a challenge. Two little
"ears" held the front end cap on the unit with small screws. The ears were
broken into several pieces and could be heard rattling around inside the
case. I could glue them back together, but the results have, in the past,
been unreliable at best.

I decided to try and reinforce the plastic. I often melt solid hookup
wire across a break (on the inside, where it doesn't show) with a
soldering iron to strengthen a glued area, but these tabs were so small, any
heat would warp them and the case would not fit back together. What to do?

I noticed once that when Superglue gets on ordinary notebook paper,
it gets hard as a rock. It is difficult to tear, but is flexible enough to
bend a little without breaking. Since one side of the little plastic ears
were essentially flat, I superglued a strip of paper on each ear. The glue
partially melted the plastic and made a good strong bond. After the glue
set up, I trimmed the edges with an Xacto knife and poked holes in the
paper for the mounting screws. The finished repair is stronger than the
original product. The paper reinforcement is thin enough that there was no
problem fitting the front back on the case.

  14.45) Putting equipment into long term storage (Self-Stor, etc.)

Electronic equipment is happiest if kept in the same type of environment that
humans like - moderate temperatures, low humidity.  What if you are forced
to store equipment for months or longer in a non-environmentally controlled
space like a public storage facility?


1. Find some long lost relatives who will store the electronics for you in
   a heated space.

If this is not possible:

2. Seal each piece of equipment in a thick plastic bag along with a pack
   of dessicant to keep it dry (that silica gel stuff you always throw away).
   This will preferably be in the original packing box (and include all
   cables, accessories, and manuals, so they won't get lost.)

Moisture is more of a problem than the absolute temperature (within
reason) or temperature fluctuations.  Therefore, avoiding the totally
damp and dingy dungeon of a medieval castle is definitely desirable.

  14.46) Dealing with a kit that was assembled by someone else a long long time ago

When you purchase a commercial piece of equipment, it is assumed that the
construction has been done properly.  This may not always be the case but
it is more likely when a million of something is manufactured than a hand
soldered kit possibly assembled by someone who barely knew which end of the
soldering iron to hold!

I picked up a Heathkit DMM at a garage sale for next to nothing that had
apparently never been quite completed.  The problem turned out to be a
defective rectifier in the power supply.  However, everything else including
the soldering was perfect.  For kits, this may be the exception :-(.  The
original owner must have given up when the DMM didn't power up properly - and
had no DMM to debug it with!

(Portions from: jmccarty@sun1307.spd.dsccc.com (Mike McCarty)

1. Look for improperly soldered joints.  Kits often are soldered by people
   with, shall we say, less than completely optimal soldering skills.  I have
   looked at kits I assembled when I was a teenager, and can't believe the
   joints were really that bad. 

2. Clean any switches or other moving contacts with some good TV tuner

3. Vacuum out any dust which may have accumulated.  I prefer that to using
   compressed air, but you may use that also; be careful of compressed air
   which may come out with a high static charge.

4. Reseat socketed components and any boards with edge connectors.  If the
   contacts look oxidized, clean them with a soft pencil eraser and/or contact
   cleaner.  Look for loose spade connectors as well.

5. Check for loose screws or other fasteners and tighten if necessary.

6. Jiggle wires and look for corrosion/fatigued wires especially where flat
   ribbon type cables are used

7. Where something is more than 10 years old (in particular), it may be a good
   idea to check and/or just replace any electrolytic capacitors which may be
   drying out.

8. Replace any primary batteries after thoroughly cleaning the battery
   contacts.  Depending on age and previous use types may also be bad as well.
   Discharged lead-acid types more than a year or two old are likely hopeless.
   However, I have found some NiCds that were quite old and perfectly fine.

9. Finally, if the equipment had possibly never been operational (i.e., you
   found the cover still in its protective plastic bag!), check ALL components
   for proper location and direction before applying power.  Of course, it may
   already be too late if there was a part installed incorrectly and the
   original owner attempted to power it up.

  14.47) Cleaning exterior surfaces

I usually start with soap and water or mild detergent.  If this does not
work, rubbing or 91% medicinal alcohol, 'Windex', and then, WD40 are tried.
All of these are usually safe for plastics though some paints or printing
may be affected - test on an inconspicuous area first.  Scouring powder and/or
sandpaper is only used as a last resort! :-)  However, in some cases, where
there is serious discoloration due to heat and ozone, these may prove somewhat

One or more of the following will probably work even for tough tobacco
smoke/tar buildup:

(From: Terry DeWick (dewickt@esper.com)).

I have found plain household ammonia works well especially since it is
cheap, if not available I use '409' or 'Fantastic' cleaners.

(From: Ralph Wade Phillips (ralphp@gcstation.net)).

'Scrubbing Bubbles' bathroom cleaner (Dow is the brand I use) works better
than anything else I've found yet, besides chucking the case.

Be sure to follow with a decent Windex-like cleaner - the residue from the
Dow cleaner will cause you to gasp every so often for the next six months!

(From: Joe (joeb@viaduct.custom.net)).

Go to SAM'S and get a jug of 'ENTNT'. Mix it in a spray bottle
with water (I like about one part ENTNT to four parts water) and
enjoy watching the nasty brown yuck drip off the monitor. Finish
the job with windex to remove the residue from the ENTNT.  The 
ENTNT is safe on plastic, but test it on painted surfaces first.

  14.48) When glue is more than glue

(From: Jim Leone (jim.leone@paonline.com)).

I have two words (no they are not plastics --- sam): Resistor Glue.

A lot of today's electronics manufacturers, before the printed circuit board
goes through the flow solder machine, use a certain type of glue to hold down
large components like heatsinks, electrolytic capacitors, and resistors.
After 2 to 3+ years of life, bonded to a high temperature component, this glue
turns conductive!!!!!!!

One blatant example of this is the Viewsonic (however many other manufacturers
use the same type of stuff) 4e Model 7033 computer monitor where the 86VDC
main rectifier on the switching supply has it's pins coated with this
'Resistor Glue'.  When the monitor was new the glue has a tan color and kind
of feels like really dried up chewing gum.  You know, the kind that has been
under a desk for 1 year.  After about 2 years, the color has changed to a
darker brown; it could be almond to dark walnut colored.  Now you should be
able to easily remove it by scraping it away with an Xacto knife, and it will
crumble away.
However, in equipment left on 24 hours a day in moderate to high heat
environments this glue takes on a more carbon hue.  Typical units have
holes burned right through the circuit board and others are left with
carbon scarred 'divits' on the board that must be gouged out to keep the
supply from arcing across.

On one hand, an optimist might say that this is a result of engineers who's
goal was to get the product out before the deadline at the end of the month.

But on the other hand, a pessimist could say that this is a result of blatant
planned obsolescence

Chapter 15) Specific Problems and Repairs

  15.1) Classic ATT Touch Tone phone 'battlewagon' will not dial properly

Typical symptoms are: everything works fine except erratic or no dialing.  For
some buttons, dial tone would not go away.  For others, tones would be
accepted but will be erratic and result in incorrect digits.  Certain digits
may sound weak, wavery, or single frequency (rather than the proper DTMF
dual tones).

(Note that this is not the same as the situation where the phone does not dial
at all - there are no tones of any kind generated.  In this case, the wires
to the phone may simply be reversed - old ATT touch tone phones will not dial
out if they are but will work in all other respects.  Modern phones generally
don't care about phone line polarity.)

While the internal wiring of these old phones is intimidating,
the basic tone dialing circuitry is an amazing example of simplicity.
About the only things that fail yet still permit some tone generation
are the pot core coils that determine tone frequency.  Therefore, this is
the first thing to check.

There are two cores which each consist of two halves glued together.
Breaks seem to be a common problem due to both the age and the brittle
cement used on some revs of this model phone, and probably, as a result
of rough treatment when hanging up the handset, or dropping or throwing
of the desk phone.

These cores must be aligned before being glued back together.  In addition,
there is an adjustment plug which may need to be tweaked.  I align by ear as
follows: Put a known good tone dialing phone and the bad phone on the same
phone line.  Momentarily depress the hook switches to silence the dial tone.
You will now have about 25 seconds before the nice polite operator recording
tells you how to make a call.  Depending on which core is bad, depress either
an entire (same) row or column of buttons on both phones.  (Adhesive tape is
handy to hold down the buttons unless you have four hands.)  By depressing the
entire set of buttons, you are disabling the other tone generator so you hear
a pure tone.  Without turning the fine adjustment plug (assuming it was not
disturbed; if it was, set it mid-range or the same as the one in the other
core), rotate the loose core top until a zero beat is obtained.  As your
rotate the core, you will hear the pitch change.  As it approaches the correct
setting, you will hear the tones beat against each other.  When you are set
correctly, the pitches will be equal and the beat frequency will go to zero.
Mark the position of the core with a pen or pencil and then glue with Epoxy or
other general purpose adhesive (around the outside - not on the mating
surfaces as this will affect the tone frequencies).  After the glue sets,
confirm and adjust the plug core if needed.  These cores use a strange
triangular core tool - I made mine by filing down an aluminum roofing nail
(do not use a ferrous material).

These classic ATT Touch Tone phones are virtually indestructible.
However, broken cores (or actually, just broken joints on the cores) are
common but easily repaired once you know what to look for.  Setting the tones
by referencing a known good phone seems to be a very reliable technique
as the zero beat permits an adjustment to better than .1%.  Note that if
the reference phone is a more modern (and flimsy digital one), then pushing
multiple buttons may not work as it does with the old analog models.  Setting
the frequency using the normal dual tones will work - it is just not as easy.

  15.2) ATT classic dial phone will not dial

I know, you haven't seen one of these in years, but I just had to throw
this in.

Most likely it was dropped - these phones simply do not seem to fail any
other way.  When dropped, assuming there is no obvious damage, a little
plastic stop inside the dial mechanism which is on a pivot flips the wrong
way.  This normally prevents dialing pulses from being generated when the
dial returns to its home position but when flipped, prevents dialing
totally.  It is real easy to flip it back into place.

  15.3) Jerrold 400 Cable Converter Problems

The most common symptoms for these cable boxes relate to their not staying
on or acting erratically when the buttons are pressed.  The causes are usually
quite simple:

1. Cold solder joints around the power supply regulator ICs (on chassis
   heat sink).

2. Dried up main filter capacitors - two large electrolytics in power supply
   on main board.

Be careful disassembling the main board from the chassis as at least one of
the regulator ICs clipped to the side of the chassis is insulated from this
heatsink and the insulation is easily damaged.

  15.4) Original Nintendo console erratic or dead

While the original Nintendo game machine is a couple of generations
out of date, many are still in use.  And, hey, kids usually don't care.

The most common problem with these units is a worn or dirty
cartridge connector.  In this case, the red power/status light will
continue to flash even after the RESET button is pressed with a
game cartridge in place.  Replacements are available for about $9
from the sources listed at the end of this document.

First, try another game cartridge - the one that is not working may
just have dirty contacts or may be defective.  Clean the contacts
with a Qtip moistened with water followed by isopropyl alcohol.
(The water will remove the sugar from the candy that may have made its
way onto the connector.)

To get inside, you first remove the 6 screws on the bottom and then
about 12 screws which fasten the circuit board and shield to the bottom
of the case.  (Note: there are two screws which are longer and silver
colored - make sure they get back to their original location when you put
everything back together.)  Once all these screws are removed, the black
connector can be slid off the edge finger on the circuit board  Inspect
these connections - they just may be a bit corroded or dirty.  Use contact
cleaner and/or a pencil eraser and see if that makes any difference.
Use contact cleaner on the dual rows of fingers that connect to the
game cartridge as well.  A dental pick can be used to gently spread the
fingers apart ever so slightly and thus improve the connection when the
cartridge is inserted.

Even if this only makes a slight improvement - you can press down on
the cartridge and the machine will respond to the RESET button - you have
confirmed that the connector is indeed the problem.  In many cases, just
this cleaning will result in reliable operation for a long time to come.

  15.5) Repairing Texas Instruments TI-5X calculators

I have them up through TI-57 so I don't know if the following applies
to models higher than this (TI-58 and TI-59).

If it hasn't been used for a while (like 15 years?) then the NiCds are
likely deader than a door nail and will not accept a charge since they
are totally shorted.  Bad NiCds is very likely all that is wrong with
the calculator.

If your calculator has a pack that plugs in inside the back with 2 AA NiCds
and some circuitry, then it is the same.

First crack open the pack by using a butter knife or similar instrument
at the catches along the seam.  You will see a pair of AA NiCds and a
small circuit board.  This is a DC-DC convertor which boosts the 2.4 V
of the NiCds to about 10 V to operate the logic of the calculator.

Inspect the circuit board for corrosion and other obvious damage.  Unless
the calculator was stored in a damp area, it should be fine.  The batteries
will probably have crusty white stuff on the positive ends.  They are bad.
Don't even bother trying to zap them.

As a test, you can do either or both of the following:

1. Get a large electrolytic capacitor (e.g., 10,000 uF at 10 V) and put it
   in in place of the batteries.  Observe polarity.  Try out the calculator
   using the TI charger/adapter.  Operations will be a bit flakey but should
   basically work (the capacitor, no matter how large, apparently will not
   substitute for the NiCds).

2. Unplug the TI battery pack and set it aside.  Find a 9 V power supply or
   a 9V battery.  Connect this to the red and black wires coming from the
   logic board connector which went to the battery pack.  NOTE: the wire
   color coding is backwards on at least some of these.  Black is positive
   for some reason.  However, nothing disasterous happens if you connect it
   backwards as far as I can tell since I was testing it backwards for quite
   a while until I caught on.  And, I thought TI was a real company! 

If these tests are successful, the calculator is likely fine and you just
need a new set of AA NiCds with solder tabs to make it as good as new.

Or, if you don't need the authenticity of a genuine TI form-and-function
rechargeable battery pack, use a 9V AC adapater, 9V Alkaline, or 9V NiCd
battery and charge it externally.

Chapter 16) Service Information

  16.1) Determining belt type and size

Belts are normally specified by their cross section - square, flat, round,
and their inside circumference (IC).  The IC is used since it is virtually
impossible to accurately measure the diameter of a belt.

Assuming you cannot locate an actual part number, determine the type of
belt; square, flat, or round.  If you do not have the old belt, this is
usually obvious from the pulleys.  Most small belts (as opposed to  V-belts
on 1 HP shop motors!) used in consumer electronic equipment are of square
cross section though flat types are sometimes found in the main drives of
VCRs, cassette/tape decks, and turntables (remember those?).  Measure or
estimate the thickness.

The IC is always specified with the belt fully relaxed.  This can be
measured by hooking the old belt on one end of a ruler and pulling it
just tight enough so that it more or less flattens out.  Read off the
length, then double it for the IC.  Get a new belt that is 5% or so smaller
to account for the old one be somewhat stretched out.  Of course, if the
belt broke, measurement is real easy.  Or, if you do not care about
the old belt, just cut it and measure the total length.

If the old belt decomposed into a slimy glob of jellatinous black goop or is
missing, you will need to use a string or fine wire around the appropriate
pulleys to determine the IC.  Reduce this by 10-25% for the replacement.
Very often the match does not need to be exact in either thickness or
length - particularly for long thin belts.  A common rubber band may in
fact work just as well for something like a tape counter!

However, there are cases where an exact match is critical - some
VCRs and belt driven turntables or tape decks do require an exact
replacement for certain drive belts but this is rare.

Some parts suppliers make determining replacement belts very easy with
the PRB system in which the part number fully codes the shape, size,
and thickness.

Making custom length rubber belts: 

The following will probably work for most drive belts except for those which
are critical for accurate speed control in devices like cassette decks and

(From: Melissa & Jim (mgkepner@facstaff.wisc.edu)).

3M and Eastman make cyanoacrylate adhesives (super glue) that are
specially made for making custom O-rings from linear stock.  This
seems to be exactly the same problem you are approaching.  These glues
work very well and produce a joint as strong as the base material, but
without the need for the needle and thread.  The joint can be made
almost invisible.  The only hard part is holding the pieces aligned
while the glue cures, but in this case that is only seconds.

I have used a machinists steel V-block for this, but one of the O-ring
manufacturers sells a plastic tool for exactly this purpose.  In the
US, I would check at a bearing supply house; they often carry O-ring
supplies as well.

  16.2) Rubber or elastic bands as drive belts?

It is 3 AM, you have finally removed the last of the 38 screws to access the
tape transport in your Suprex Never-Forget model X4123 answering machine and
what do you fine?  A broken belt, of course!  What to do?

As a test at least, a common elastic band may work.  The recordings will likely
have terrible wow and flutter but this will at least confirm that there is
nothing else broken.  In a pinch, this free solution can be left in place until
a proper replacement arrives.  This should work for many types of devices - CD
players, VCRs, tape decks, etc. - where grooved pulleys are used and the belt
is not called on to provide a great deal of power.

  16.3) Interchangeability of components

The question often arises: If I cannot obtain an exact replacement or
if I have a VCR, tape deck, or other equipment 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, X-ray protection and to minimize fire hazards.
However, these components are not very common in audio equipment or other
consumer devices (other than TVs, monitors, and microwave ovens) except for
possibly in their power supply.

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.

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.  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.  It is best to use the same 
    type - metal film resistor, for example.  But for testing, even this is
    not a hard and fast rule and a carbon resistor should work just fine.

3.  Potentiometers - user knobs usually control one or more of these.  There
    are four considerations in locating a suitable replacement: resistance,
    and taper, power rating, configuration, and mechanical fit.  Configuration
    refers to the number of ganged pots, concentric knobs, etc.  Matching
    this from your junk box may prove to be the toughest challenge!  Many
    of the controls for audio equipment use what is known as an 'audio taper'.
    This means that the resistance change with knob rotation is not linear
    but is designed to produce a uniform incremental change in perceived
    volume, for example.  Replacement with a linear taper pot will squish
    all of the effect towards one end of the range but it will still work.
    If measuring the resistance of a (good) potentiometer with its wiper
    set in the middle results in significantly different readings from center
    to each end, it is most likely an audio taper pot (though some other
    weird taper or other peculiarity is possible).

4.  Rectifiers - many are of these are high efficiency and/or fast recovery
    types.  Replacements should have equal or better PRV, If, and Tr
    specifications.  For line rectifiers, 1N400x types can usually be used.

5.  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 ratings are not exceeded.  However, performance may not be quite
    as good.  For power types, make sure to use a heatsink.

6.  Switching power supply transistors - exact replacement is generally
    best but switchmode transistors that have specifications that are at
    least as good will work in many cases.  See the documents:  "Notes on the Troubleshooting and Repair of Television Sets", "Notes on the Troubleshooting and Repair of Computer and Video Monitors", and "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies"
    for more info.

7.  Audio and erase heads - may be possible if the mountings are reasonably
    compatible.  However, there could be other unknowns like coil impedance
    and drive requirements.  The connectors are not likely to be similar
    either.  There are usually significant differences in head configuration
    and mounting arrangement between 2 head, 3 head, and autoreverse cassette
    or open reel tape decks.

8.  Motors - small PM motors may be substituted if they fit physically.
    Make sure you install for the correct direction of rotation (determined
    by polarity).  Capstan motors - especially the direct drive type - are
    probably not interchangeable.  However, generic speed regulated
    cassette drive motors are available.

9.  Sensors - many are sufficiently similar to permit substitution.

10. 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.

11. Belts, tires, and pinch rollers - a close match may be good enough at
    least to confirm a problem or to use until the replacements arrives.

12. 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, interstage coils or transformers, microcontrollers,
other custom programmed chips, display modules, and entire power supplies
unless identical.

  16.4) Why are there parts missing from my equipment?

It is not uncommon for parts to be missing from production equipment due
to design changes or field mods.  Thus, it may not mean anything.  Inspect
the solder pads - if they look the same as all the others, it was probably
never installed in the first place.  Of course, that could have been a
manufacturing omission as well.  Parts just don' jump ship without leaving
evidence behind!

Don't be tempted to add a part just because there is an empty spot.  In
some cases, like the RCA TV that would tend to blow HOTs if the power failed,
that would be a really bad idea and complicate your troubleshooting.

Whole blocks of circuitry are often left unpopulated on lower priced models.
You didn't pay for those features.  Sometimes, this can work to your advantage
enabling you to upgrade to a fancier model for the cost of the parts.

  16.5) Web resources

Tandy (Radio Shack) has a nice web resource and fax-back service.  This is
mostly for their equipment but some of it applies to other brands and there
are diagrams which may be useful for other manufacturers' VCRs, TVs, CD
players, camcorders, remote controls, and other devices.

 http://support.tandy.com/                          (Tandy homepage) http://support.tandy.com/audio.html                (Audio products) http://support.tandy.com/video.html                (Video products)

Since Tandy does not manufacture its own equipment - they are other brands
with Realistic, Optimus, or other Radio Shack logos - your model may actually
be covered.  It may just take a little searching to find it.

  16.6) Some general references

Here are some suggested titles that might be found in your local public
library or a technical bookstore.

1.  Troubleshooting and Repairing Electronic Circuits
    Robert L. Goodman
    Second Edition
    TAB Books, Inc., 1990 
    Blue Ridge Summit, PA 17294-0214

2.  Small Electric Motors
    Rex Miller and Mark Richard Miller
    Second Edition, 1992
    MacMillan Publishing Company
    866 Third Avenue
    New York, NY 10022

3.  Repairing Quartz Watches
    Henry B. Fried
    American Watchmakers Institute Press, 1988
    Cincinati, OH
    ISBN 0-918845-06-8

4.  Readers Digest Fix It Yourself Manual
    The Readers Digest Association, 1996
    Pleasantville, New York/Montreal
    ISBN 0-89577-871-8

5.  The Complete Guide to Digital Audio Tape Recorders
      including Troubleshooting TIps
    Erik S. Schetina
    P.T.R. Prentice Hall,
    Englewood Cliffs, NJ 07632
    ISBN 0-13-213448-9

6.  DAT - The Complete Guide to Digital Audio Tape
    Delton T. Horn
    TAB Books, Inc., 1991
    Blue Ridge Summit, PA 17294-0214
    ISBN 0-8306-7670-8 (hardcover), ISBN 0-8306-3670-6 (paperback)

7.  Troubleshooting and Repairing FAX Machines
    Gordon McComb
    Tab Books, a division of McGraw-Hill, Inc., 1992
    Blue Ridge Summit, PA 17214
    ISBN 0-8306-7778-X (hardcover), 0-8306-3778-8 (paperback)

8.  Complete Guide to Home Entertainment Equipment - Troubleshooting and Repair
    John D. Lenk
    Prentice Hall, Inc., a division of Simon and Schuster, 1989
    ISBN 0-13-161001-5

9.  Understanding Telephone Electronics
    Fike and Friend

10. Installing Telephones
    Radio Shack
    Catalog number: 62-1060

11. All Thumbs Guide to Telephones and Answering Machines
    Gene B. Williams
    TAB Books, Inc., 1993
    Blue Ridge Summit, PA 17294-0214
    ISBN 0-8306-4435-0 (paperback)

    This one is very basic but does cover the most common problems and has
    illustrated instructions for general telephone wiring, adding extensions,
    answering machine cleaning, rubber parts, simple electronic problems, etc.

And, for that older audio equipment (including record changers):

12. Repairing Home Audio Systems
    E. Eugene Eckland
    McGraw-Hill Book Company, 1962
    Library of congress catalog number: 61-18021

  16.7) Recommended parts suppliers

For general electronic components like resistors and capacitors, most
electronics distributors will have a sufficient variety at reasonable
cost.  Even Radio Shack can be considered in a pinch.

However, for consumer electronics equipment repairs, places like Digikey,
Allied, and Newark do not have the a variety of Japanese semiconductors
like ICs and transistors or any components like tape heads or belts.

The following are good sources for consumer electronics replacement parts,
especially for VCRs, TVs, and other audio and video equipment:

* 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/

* Dalbani                         (Excellent Japanese semiconductor source,
  U.S. Voice: 1-800-325-2264.      VCR parts, other consumer electronics,
  U.S. Fax: 1-305-594-6588.        Xenon flash tubes, car stereo, CATV).
  Int. Voice: 1-305-716-0947.
  Int. Fax: 1-305-716-9719.
  Web: http://www.dalbani.com/

* Premium Parts                   (Very complete VCR parts, some tools,
  U.S. Voice: 1-800-558-9572.      adapter, cables, other replacement parts.)
  U.S. Fax: 1-800-887-2727.
  Web: http://www.premiumparts.com/

* Computer Component Source       (Mostly computer monitor replacement parts,
  U.S. Voice: 1-800-356-1227.      also, some electronic components including
  U.S. Fax: 1-800-926-2062.        semiconductors.)
  Int. Voice: 1-516-496-8780.
  Int. Fax: 1-516-496-8784.

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]