Contents:
Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff
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:
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.
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 devices. For general troubleshooting techniques, see the section: "Some general references".
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)
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).
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 contact. * 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!
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.
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!
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 wiring. 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 pliers. * 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!
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.
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.
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 console. 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.
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.
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 tape. 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.
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.)
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.
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.
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 machine. 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.
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!
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.
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" :-)
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 Eraser. 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 !!!
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 transport!
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.
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.
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 microscrews.
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.
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.
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.
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.
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.
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.
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 spills.
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.
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... Tadah.... 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!
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.
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 supply. (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.
"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.
"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.
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)
(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.
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.
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.
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.
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 recordings. 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.
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.
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.
(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.
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 records. 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) :-(.
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).
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.
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 found. 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 confirmation.
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
damage.
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.
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.
(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 1-616-285-1144. (From: Ray