Repair Briefs, an Introduction V1.00

• 1) About the Author
• 2) Introduction
• 3) Some of My Rules of Troubleshooting
• 4) Tools, Test Equipment, and Other Stuff
• 4.1) Some basic hand tools
• 4.2) Basic test equipment
• 4.3) Handy widgets
• 4.4) Basic Ancillary Equipment
• 4.5) Chemicals
• 4.6) Adhesives
• 4.7) Parts
• 5) Sources of Information
• 5.1) Manufacturer's service literature
• 5.2) SAM's Photofacts
• 5.3) Inside cover of the equipment
• 5.4) Parts information
• 5.5) On-line Repair Notes and Guides
• 5.6) Last Resort
• 6) Safe Troubleshooting

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

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

Not all of these will be exciting cast of thousands repairs. Many will be mundain but will address common problems with consumer electronic equipment. There will probably even be some of those 'dogs' that we all hate - the problems that never seem to go away. In any case, these will all be based on my true experiences with minimal embellishment.

Safety First

You should know the hazards associated with the equipment you are troubleshooting. Take all safety precautions. Expect the unexpected. Take your time.

Always think 'what if'.

This applies both to the analytic procedures as well as to precautions with respect to probing the equipment. When probing, insulate all but the last 1/8" of the probe tip to prevent costly shorts. (If I had a nickel for every time I have been screwed not following this advice...)

Learn from your mistakes.

We all make mistakes - some of them can be quite costly. A simple problem can turn into an expensive one due to a slip of the probe or being over eager to try something before thinking it through. While stating that your experience in these endeavors is measured by the number of scars you have may be stretching the point, expect to screwup - we all can point to that disaster due to inexperience or carelessness. Just make it a point not to make the same mistake again.

How you approach matters.

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 VCRs, CD player, tape decks, and answering machines 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.

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).

Many problems have simple solutions.

Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a TV, it may just be a bad connection or failed diode. For a VCR, it may just be a bad belt or idler tire - or an experiment in rock placement by your 3-year old. For a CD player, a dirty lens or need for lubrication. Try to remember that the problems with the most catastrophic impact on operation - a dead TV or a VCR that eats tapes - usually have the simplest solutions. The kind of problems we would like to avoid at all costs are the ones that are intermittent or difficult to reproduce: subtle color noise, the occasional interference, or the dreaded horizontal output transistor blowing out every 3 months syndrome.

Whenever possible, try to substitute a working unit.

With modular systems like component stereos and computers, narrowing down a problem to a single unit should be the first priority. This is usually safe to do in such cases and will quickly identify which unit needs work. This same principle applies at the electronic or mechanical parts level. Note that there is the possibility of damaging the known good part by putting it into a non-working device or vice versa. This risk is most likely with the power circuitry in amplifiers, TVs and monitors, power supplies, etc. With appropriate precautions (like the series light bulb) the risk can be minimized.

Don't blindly trust your instruments.

If your get readings that don't make sense, you may be using your equipment in a way which is confusing it. DMMs are not good at checking semiconductors in-circuit or the power transistor you are testing may have a built in damper diode and/or base resistor. Your scope may be picking up interference which is swamping the low level signal you are searching for (TVs and Monitors, or low level circuits in VCRs and CD players). Your frequency counter may be double triggering due to noise or imperfect signal shape.

Confirm the problem before diving into the repair.

It is amazing how many complaints turn out to be impossible to reproduce or are simple cockpit error. It also makes sense to identify exactly what is and is not working so that you will know whether some fault that just appeared was actually a preexisting problem or was caused by your poking. Try to get as much information as possible about the problem from the owner. If you are the owner, try to reconstruct the exact sequence of events that led to the failure. For example, did the TV just not work when turned on or were there some preliminary symptoms like a jittery or squished picture prior to total failure? Did the problem come and go before finally staying bad for good?

Invest in good tools.

If you are into garage sales, you can often pick up excellent well maintained tools very inexpensively but be selective - there is a lot of junk out there. In the end, sub-standard tools will slow you down and prove extremely frustrating to use. Keep your tools healthy - learn to use a wet-stone or grinding wheel where appropriate (screwdrivers, drill bits, etc.) and put a light film of oil (e.g., WD40) on steel tools to prevent rust.

Screwdrivers, common ...

Screwdrivers of all types and sizes including straight, Philips, Torx.

Screwdrivers, Jewelers...

screwdrivers - both straight and Philips.

Small socket drivers.

Allen (Hex) key

Hex key wrenches or hex drivers. Miniature metric sizes for VCRs.

Pliers

Long nose, round nose, curved. Both smooth and serrated types are useful.

Wrenches

Adjustable wrench (small).

Wire Cutters

Diagonal and flush. Linesman pliers.

Wire strippers

fixed and adjustable. Crimp tool.

Alignment tools

(at least a standard RCA type for coils).

Files

Small set of assorted types including flat, round, square, and triangular.

Soldering equipment

A low wattage (25 W) iron for delicate components (e.g., ICs, small parts), a medium wattage (40-50W) iron for heavy duty circuit board work (e.g., power plane connections, transformers), and 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 de-soldered connections. A vacuum rework station is not needed unless you are removing your soldered in 500 pin Intel P6!

(From the Editor - for those in/around the USA only!)

I have found the Radio Shack one-piece desoldering iron to be excellent. It's a 35Watt pen iron with a long tube, a vacuum bulb, and a tip. The tips are replaceable and come in copper or iron-plated designs. The later last a lot longer. I have de-soldered 24 pin EPROMs from 4 layer boards with EXCELLENT results. Of course, practice first on scrap.

Magnetic pickup tool

You can never tell when you will drop something deep inside a VCR. If you keep a strong magnet stuck to your workbench, you can use it to magnetize most steel tools such as screwdrivers. Just keep anything magnetized away from the tape path and magnetic heads.

Hand drill, electric drill, drill press - one or all.

A small bench-top drill press (e.g., 8") is invaluable for many tasks. A good set of high speed bits (not the 1000 bits for $9.95 variety). Also, miniature bits for PCB and small plastic repairs.

DMM and/or VOM

I prefer to have both. A good old Simpson 260 is better in many ways than a cheap digital multi-meter. For most measurements, I still use a 25 year old Lafayette (remember them?) VOM. I only go for the DMM when I need to measure really low ohms or where better accuracy is needed (though this can be deceptive - just because a DMM has 3-1/2 digits does not mean it is that accurate - check you manual, it may prove enlightening). The Simpson 260 also has a nice 5000 V AC/DC scale which the others lack.

Scales for transistor, capacitor, frequency counter, etc. are not really essential. A diode test function on a DMM is needed, however, to properly bias semiconductor junctions. Even this is not useful for in-circuit tests or for some power transistors or transistors with built in damper diodes and/or base resistors.

Make sure you have a good well insulated set of test probes. This is for your own safety as you may be measuring relatively high voltages. Periodically inspect for damage and repair or replace as needed.

A high impedance high voltage probe is sometimes useful for TVs and monitors. You can build one of these which will suffice for most consumer electronics work.

Oscilloscope

Dual trace, 10-20 MHz minimum vertical bandwidth, delayed sweep desirable but not essential. A good set of proper 10x/1x probes. High vertical bandwidth is desirable but most consumer electronics work can be done with a 10 MHz scope. If you get into digital debugging, that is another story - 100 MHz and up will be required. If money is no object, get a good digital storage scope. You can even get relatively inexpensive scope cards for PCs, but unless you are into PC controlled instrumentation, a stand-alone scope is much more useful.

I would recommend a good used Tektronix or HP scope over a new scope of almost any other brand. You will usually get more scope for your money and these things last almost forever. My 'good' scope is the militarized version (AN/USM-281A) of the HP180 lab scope. This has a dual channel 50 MHz vertical plug-in and a delayed sweep horizontal plug-in. I have seen these going for under $300 from surplus outfits. For a little more money, you can get a Tek 465 100 MHz scope ($400-700) which will suffice for all but the most demanding (read: RF or high speed digital) repairs.

TV set

(color is desirable) and/or video monitor for testing of video equipment like VCRs, camcorders, laser disc players, etc.

VCR

or other video signal source for testing of video monitors and TVs.

Stereo tuner

or other audio signal source for testing of audio equipment.

Audio signal generator

A function generator (sine, square, triangle) is nice as well. The usual audio generator will output from a few Hz to about 1 MHz.

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.

RF signal generator

For serious debugging of radio and tuner front-ends. These can get quite sophisticated (and expensive) with various modulation/sweep functions. For most work, such extravagance is unnecessary.

LCR meter

A capacitor tester is desirable but I prefer to substitute a known good capacitor rather than trusting a meter which will not test under the same conditions as in-circuit.

Adjustable power supplies

At least one of these should be of the totally indestructible variety - one you can accidentally short out without fear of damage. Mine is a simple 1 amp 0-40 V transformer and rectifier/filter cap affair with a little Variac for adjustment.

Series light bulb

... for current limiting during the testing of TVs, monitors, switching power supplies, audio power amplifiers, etc. I built a dual outlet box with the outlets wired in series so that a lamp can be plugged into one outlet and the device under test into the other.

Variac

It doesn't need to be large - a 2 A Variac mounted with a switch, outlet and fuse will suffice for most tasks. However, a 5 amp or larger Variac is desirable. If you will be troubleshooting 220 VAC equipment in the US, there are Variacs that will output 0-240 VAC from a 115 VAC line.

(From the Editor)

DANGER!! Variac, an autotransformer, does NOT isolate you in any way from the 120V line! If you NEED isolation, please see next section.

120VAC ------------------    (120VAC output if here)
                         )
                        (
                         )
                        (
                         )
                        (
                         ) <--------------- OUTPUT 1
                        (
                         )
                        (
                         )   (0VAC output if here)
120VAC ------------------+----------------- OUTPUT 2

Isolation transformer

This is very important for safely working on live chassis equipment. You can build one from a pair of similar power transformers back-to-back. I built mine from a couple of old tube type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage windings were connected together. The unused low voltage windings can be put in series with the primary or output windings to adjust voltage.

(From the Editor)

BTW, in the USA, used 250VA isolation transformer can be had for under $100... Sit down when you price new ones ;-)

Video cassette cheater

This is the shell of a VHS or Beta cassette with all of the innards removed and most of the top and bottom cut out to permit access to the reel spindles and other rotating components of a VCR during operation. You can also purchase these at grossly inflated prices.

Degaussing coil

Make or buy. The internal degaussing coil salvaged from a defunct TV doubled over to half it original diameter to increase its strength in series with a 200 W light bulb for current limiting will work just fine.

Tape head demagnetizer

This could just be a coil wrapped around a common nail with its end protected with tape. Connect to low voltage AC. However, these are so inexpensive that you should just buy one. Caution: do not use on video heads unless specifically designed for them. Some are strong enough to damage the fragile ferrite cores.

Clip leads

Like woodworking clamps, you can never have too many of these.

Patch cords

... for audio, video, and telephone interconnection.

Printer

Centronics printer and serial computer cables.

IR detector

This can be a photodiode/LED circuit or IR sensitive card. Use for testing remote controls, IR LEDs in photo-sensors, and CD laser-diodes.

Flyback tester

I use a 12 V chopper with a 10 turn coil to excite the flyback under test. This will identify most primary and secondary short type faults under near-operating conditions.

Insulating sheets

For separating circuit boards when removed from the chassis. These can be cardboard, fiberglass, plastic, etc.

Insulating sticks

For prodding to locate intermittents.

Small parts tray and container

I always use a film canister or pill bottle for storing the screws, washers, and springs removed during disassembly. An ice-cube tray or egg carton makes a handy parts bin for temporary storage of small parts while you are working.

TVs

VHF and UHF antennas and/or VCR or other video source with both RF and baseband (RCA plugs) outputs.

VCRs

A small TV (preferably color but a monochrome TV will suffice for many tests) and/or NTSC/PAL video monitor, antenna, known good video tapes at both SP and SLP speeds. Also, a couple of blank cassettes for record tests.

Camcorders

Same as VCRs but in addition, a test chart, tripod, and lamps for indoor testing.

CD and Laser-disc Players

A garbage CD and test CD (or Laser-discs). A garbage disc is one you do not care about if it gets scratched. A test disc does not need to be an official (and expensive) test disc - any known good disc will do for most tests. The garbage CD can even be an outdated CD-ROM - an audio CD player will usually read the directory of a CD-ROM just like an audio CD. An audio amplifier with speakers or headphones will be needed for the audio tests, or headphones if the unit has a headphone jack. A TV or video monitor will be needed for Laser-disc video tests.

Audio Equipment

A set of known working stereo components consisting of at least a tuner, amplifier, and speakers. Headphones are also useful. For most purposes, an inexpensive setup is preferred since there is no telling what kind of abuse it may need to endure during troubleshooting. I suppose that a turntable may even be needed occasionally. A couple of pre-recorded audio cassettes are handy when testing tape decks. One of these should have a tone of known frequency recorded on an accurately calibrated deck for setting tape speed. Also, a couple of blank cassettes for record tests.

Microwave Ovens

A cup of water for a load. A thermometer for power tests. Neon or incandescent bulbs with their leads shorted together can serve as microwave detectors inside the oven (though these may not always survive for very long).

PCs and components

A working basic PC is useful to serve as a testbed for trying suspect components. I use an old 286 main-board with just enough to boot from an old hard drive. A set of known working basic PC peripheral boards is useful - SVGA, IDE and MFM HD and FD controller, I/O ports, sound card and speakers, 5-1/4" and 3-1/2" floppy drives, etc. A spare power supply - even one that is not an exact mechanical match - is also handy for testing. An old laptop (commonly used as a door stop) is useful for testing printers on location.

Computer Monitors

A test PC is useful as a video source. Of course, it will need to support whatever scan rates and video types the monitor is designed to accept. Programs are available to display purity, convergence, focus, color, and other test patterns.

Telephones, answering machines, faxes

A phone line simulator is useful for initial tests. A pair of normal phone lines will work but of course you will need to provide jacks where you are working and access (which may be difficult with teens in the house).

• Light oil such as electric motor oil or 3-In-One. WD40 may be useful for cleaning or freeing rusted screws but it is not a general purpose lubricant despite what is claimed on the label.

• Light grease suitable for fine electronics - must be plastic-safe.

• Isopropyl alcohol (91 % medicinal or pure). Q-tip swabs for cleaning of everything BUT video heads; chamois head cleaning sticks for video heads. Note that sometimes plain water will work better for sugar based coatings. Tape head cleaner can be used for head cleaning as well.

• Contact cleaner in spray can

• Tuner cleaner and lubricant in spray can.

• Degreaser in spray can.

• Silicone heat sink compound

You can also see the article Chemicals used in Electronics/Repair Info (http://www.paranoia.com/~filipg/HTML/FAQ/BODY/F_Chemistry.html) for some more information... especially on contact enhancers and WD-40

• Two part fast setting Epoxy.
• General purpose adhesive like Duco Cement.
• Semi-flexible adhesive like windshield sealer.
• Flexible adhesive like weather strip cement or clear silicone sealer.
• Solvent type plastic cement.
• Rubber cement.
• Plastic electrical tape.
• Masking tape.
• Clear plastic tape.

The idea is to have enough parts available so that you do not need to raid the local electronics store every time you want to try something. A good source for many of the basic parts is dead equipment - their organs can live on at your workbench.

• Resistor assortment. Resistor packs for digital termination.

• Potentiometers (variable resistors), assorted values.

• Capacitor assortment - ceramic and electrolytic. Large high voltage electrolytics for power supplies.

• Rectifiers - 1N4007s for primaries of power supplies. Microwave oven rectifier. Fast recovery rectifiers - for switching supplies.

• Diodes - 1N4148 signal diodes.

• Transistors (bipolar): small signal, medium power, high power audio, and horizontal output transistors. Obviously, this list could get quite long. A few basic types will suffice in a pinch.

• Fuses - 3AG size (1-1/4"x1/4") - .5, 1, 2, 3, 5, 10 amp. You can always solder these across the smaller 5x20 mm fuses often found in consumer equipment these days.

• LEDs and indicator lamps.

• Wire: assorted colors of #24, #18, and #14 stranded and solid insulated wire. 75 ohm coax for video. Shielded cable for audio. Fine wire (e.g., #30, bare and insulated) for PCB repairs.

• Line cords, plugs, and other electrical components.

• Assorted small switches - toggle, pushbutton, etc.

• Various jacks and plugs such as RCA, phono, F, BNC, etc.

• Small loudspeakers, headphones.

• Hardware assortment including English and Metric screws, nuts, bolts, flat and lock washers.

• etc., etc., etc.

SAM's are often available (for photocopy costs) from you local large public library which may subscribe to the complete series. If not, a large electronic distributor can order the selected folder for you.

One advantage of the SAM's info is that it is compiled in a very consistent format so that once you are familiar with one model TV, it is easy to transfer that knowledge to any other. They provide waveforms at key locations and DC voltage measurements almost everywhere. Additional info such as coil resistance is often provided as well. The manufacturer's service manuals are generally not nearly as complete.

(BTW, I have no connection with SAM's.)

Microwave ovens almost always have a schematic diagram of the microwave power generation circuitry pasted inside the sheet-metal cover. This will always include the high voltage transformer, interlocks, rectifier, capacitor, and magnetron. Since most microwave oven problems are in these areas, this is all you are likely to need. The controller, especially electronic units, is often omitted or only covered superficially.

Check the Appliance/Electronics Repair Notes & Guides (http://www.paranoia.com/~filipg/HTML/FAQ/BODY/Repair.html) that I keep on-line. A number of them have been written by the author of this article, Samuel M. Goldwasser!

Posting to sci.electronics.repair is a bit different - speculation is safer. There is enough cross-checking such that any gross errors in analysis will be uncovered. There is also generally no profit motive. If your speculation is totally bogus, you will find out quickly enough, turn various shades of red - and learn from the responses.

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.
• 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. In a TV or monitor, if you are removing the high voltage connection to the CRT (to replace the flyback transformer for example) first discharge the CRT contact (under the insulating cup at the end of the fat red wire). Use a 1M-10M ohm 1W or greater wattage resistor on the end of an insulating stick or the probe of a high voltage meter. Discharge to the metal frame which is connected to the outside of the CRT.
• 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 are 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.
• 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!