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Electronics repair page

    Electronics repairing information

    This page is intended to be used by electronic technicians and other people who know what they are doing. Electronic equipment contains dangerous voltages and can be hazardous to unqualified service personnel. Only those with adequate training, equipment, facilities and experience should attempt to repair any electronic equipment. The information offered on these pages is intended for electronic professionals only. Anyone not qualified or lacking the equipment, facilities or experience for proper and safe electronic repair should consult with a electronic repair professional.

    Anyone attempting to repair any electronic equipment who does not fully understand the shock hazards, as well as the fire hazards associated with working with electronic equipment, should not attempt such procedures! Improperly attempted repair can kill you and burn down your house.Devices that plug into the wall can produce a very lethal electric shock as well cause a fire from incorrect or careless repairs both during servicing or later on.Improper repair of battery operated devices can also result in bad consequences for you, the device, and any equipment attached to it.

    Why some people do repairs themselved then? If you can do the repairs yourself, the equation changes dramatically asyour parts costs will be 1/2 to 1/4 of what a professional will chargeand of course your time is free. The educational aspects may also beappealing. You also will learn a lot in the process.

    Before attempting to repair anythign, learn some electronic theory and fundamentals, so that you will notinjure or kill yourself, and so you will know a bad part when you find one. It is critically important to understand theory of operation and signal-flow if you are to have any hope of repairing most equipment. You need also suitable tools:

    • Buy a relatively inexpensive digital multimeter. Learn how to use the multimeter to measure resistance, voltage, and current. A multimeter is an essential tool for all electronics repairs.
    • An oscilloscope would also be most useful. Learn how to use the oscilloscope to observe and analyze waveforms. Oscilloscope is needed in many electronics repairs.
    • Buy a soldering iron, solder, and desoldering equipment. Learn how to solder and unsolder without damaging the circuit board.
    • Find a source where you can buy the replacement parts you need.
    • You need to have general tools like screwdivers etc. to open equipment cases and removing components.

    In oder to be able to do electronics device servicing safely, you need to know what you are doing and have some safety devices in your workbench.

    Please also note the safety on your workplace.

    • Don't work alone - in the event of an emergency another person's presence may be essential.
    • Set up your work area away from possible grounds that you may accidentally contact
    • Have a fire extinguisher rated for electrical fires readily accessible in a location that won't get blocked should something burst into flames.
    • Wear eye protection - large plastic lensed eyeglasses or safety goggles.
    • Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system.
    • Set up your work area away from possible grounds that you may accidentally contact.
    • If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to.
    • Use an isolation transformer if there is any chance of contacting line connected circuits.
    • The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea.

    Floating supply in form of safety isolation transformer isused in electronics laboratories to isolate the electronicsequipment being tested or repaired from the mains supply. There are totally floating safety isolating transformers that supply 120/230 volts floating with respect to ground. These are intended for use by test/service engineers working on live mains-supplied equipment. The term 'safety' is relative of course - whilst it is perfectly safe to connect yourself to any single point of such a floating circuit it won't give you any extra protection if you were to touch both live and neutral atthe same time! In other words they only give protection against injury to people who know what they are doing - two strikes and you're out! However an isolating transformer should only be used for a singlepiece of kit. The safety relies on the integrity of the isolation of the entire supply on the secondary side of the transformer. The use of isolated supplies for testing of mains voltage equipment isprimarily to allow the use of older oscilloscopes on live chassis without causing expensive electronic explosions.

    It is a good idea to have an earth leakage protector (RCD / GFCI) to safeguard the power feed to yout desk. This device will shut down the mains power (at least in most cases) if you happen to touch the incoming power live wire. The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but may 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. Please note that GFCI may nuisance trip on some cases. A suitsble fusing on the outlets that you use to power equipment is a good idea. A fuse or circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. However, these devices may save your scope probe ground wire should you accidentally connect it to a live chassis.

    And also consider the ESD issues at your working place, get an ESD safe mat for your table and other things needed. Electronics inside many equipment nowadays is very ESD sensitive. When handling static sensitive components, an anti-static wrist strap is recommended. Use a commercially made anti-static wrist strap that has a high resistance path between you and the groundign point (greater than 100K ohms, usually 1 Mohm).

    Be careful whatever you do. 'Carelessness' is a the majority cause of accidents. 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. Never assume anything without checking it out for yourself! Don't take shortcuts! Perform as many tests as possible with power off and the equipment unplugged. Do not assume that the chassis is a suitable ground for your test equipment! Since electrocution is permanent it only takes one unluckyinstance of carelessness in an entire career to terminate your contract!

    There are simple and more complicated problems. A lot of times when an equipment stops working a fuse has blown. The fuse is there to prevent a fire in case of an excessive current draw inside the unit. Often there is a reason for the fact that fuse blew. So you need to sort out the problem before putting the new fuse in and trying the equipment. Remove what caused the fuse to blow (for example overload in using the equipment). Do not put a new fuse in unless you know that the device you are repairing is ok. By replacing the fuse and not first determining what caused it to blow, you likely caused further damage each additional time the fuse blew. When replacing the fuse remeber to put in the fuse with same rating (same current rating, same or higher voltage rating) and same type (fast or slow).

    Visual inspection is a powerful tool in many electronics repair. You can find some bad connections by marks of heating seen around the connection and you can find many mechanical faults in this way. The possibility of finding a failed component with visual inspection depends on how long the short circuit current flowed for and how hot the component became if it went with a big short. Sometimes components are SEVERELY blown (blown capacitor, tops blasted off chips, cracked chips, scorched, charred, colors turned black, that sort of thing). Most other faults will not show at all for a visual inspection. Although "eyeballing a fault" is a common practice and solves many problemswith electronics, it does have it's limitations and more test techniques areneeded to further isolate the problem. Sometimes failed component can be found when it becomes noticably hotter (heats too much) or colder (does not heat as in normal operation) than it is normally used to be. Usually in electronics repair you need a multimeter and oscilloscope to test the operation of the circuit.

    High voltages on the equipment can be dangerous. Perform as many tests as possible with power off and the equipment unplugged. 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 to 500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K to 100K ohm resistor). After discharging erify that there is no residual charge with a suitable voltmeter. 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, use test probes that avoid the possibility of an accidental short which could cause damage to various components. If you have probes that can cause shorts and you can't change them, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short. Is ia a very good idea to clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand.

    It is always essential to test AFTER any repairs to assure that no accessible parts of the equipment have inadvertently been shorted to a Hot wire or live point in the power supply. Checking for correct hookup of the Hot, Neutral, and Ground wires to the AC plug should also be standard procedure. In addition to incorrect rewiring, this could result from a faulty part, solder splash, or kinked wire insulation. There are two sets of tests that are commonly used:

    • DC leakage: Use a multimeter on the highest OHMS range to measure the resistance between the Hot/Neutral prongs of the wall plug (shorted together and with the power switch on where one exists) to ALL exposed metal parts of the equipment including metallic trim, knobs, connector shells and shields, VHF and UHF antenna connections, etc. This resistance must not be less than 1 M ohm. For the most reliable results you should a special insulation resistance meters (those typically use 250V or 500V voltage for measuring).
    • AC leakage: Connect a 1.5K ohm, 10 Watt resistor in parallel with a 0.15 uF, 150 V capacitor to act as a load. Attach this combination between the probes of your multimeter. With the equipment powered up, check between a known earth ground and each exposed metal part of the equipment as above. The potential measured for any exposed metal surface must not exceed 0.75 V. This corresponds to a maximum leakage current of 0.5 mA. A true RMS reading multimeter should be used for this test, especially where the equipment uses a switchmode power supply which may result in very non-sinusoidal leakage current.
    If the equipment fails either of these tests, the fault MUST be found and corrected before putting it back in service. Take care not to touch anything until you have confirmed that the leakage is acceptable - you could have a shocking experience!

    Know your equipment. There are special considerations for working on most televisions and other equipment not using a built-in isolation transformer. Most servicers use an isolation transformer for any AC-powered unit under test. Learn the appropriate safety considerations for using the tester and 'scope. 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. TVs and monitors have capcitors that chan hold charge for long time after the equipment is powered off. If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a suitable 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 first discharge the CRT contact contact (it is under the insulating cup at the end of the fat red wire, use a 1M to 10M ohm 1W or greater wattage resistor on the end of an insulating stick to discharge it to equipment chassis ground). 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. Always wear eye protection.

    Check the liability issues. Remember always that your are personally responsible for any safety problems you cause, or those which you should have noticed and failed to correct. So if you work on a TV and it burns down your friend's house in the middle of the night becauseof something you missed or that you caused, they can sue you, even years later. Treat the job as if it were going to be inspected afterwards and graded for neatness.

      General information

      • Desoldering - how to remove a component - If you have gotten into the act of building kits, you are inevitably going to face the situation where you need to remove a component that you have soldered on to a pc board. Whatever the case, your desoldering technique can make the difference between a successful effort and a damaged pc board. This guide is for conventional components although some of the steps may be applied to the removal of surface mount components.    Rate this link
      • Essential Tools - This article details of some of the essential tools you should have in your toolkit if you want to construct electronic circuits or repair electronics devices. The most essential tool is of course the soldering iron, so later in this article there is some guidance on choosing one and some tips on how to master the techniques of soldering.    Rate this link
      • How to trace out schematics - Tracing out the schematic of a vintage effect is not all that hard to do and has many of the elements of a detecting job. It's always interesting to figure out how an old, unusual circuit works; it may be an effect saver if you have something unusual that you can't find a schematic for that is broken. This process works well with single sided boards.    Rate this link
      • Safety Guidelines for High Voltage and/or Line Powered Equipment    Rate this link
      • The Basic De-soldering Guide Photo Gallery (and Black Museum of Bad Soldering) - De-soldering is required when electronic components need to be removed from a circuit, usually because they are faulty. This photo sequence illustrates the basic steps for desoldering a printed circuit board, in order to remove a faulty part. Both a desoldering pump as well as desolder braid are illustrated    Rate this link

      TV

      A basic knowledge of how a TV set works and what cango wrong can be of great value if you have a broken TV,even if you do not attempt the repair yourself. It will enable you to intelligently deal with the service technician. TVs can be dangerous.Inside TV there are power circuits that can take their toll on circuit components when something goes wrong. Many TVs in use today are still "Hot Chassis", one side of the AC line is connected to the circuit common. Be prepared for this. Most problems occur in the horizontal deflection and power supply sections.These run at relatively high power levels and some components run hot.The high voltage section is prone to breakdown and arcing as a resultof hairline cracks, humidity, dirt, etc.Also bad solder connections are recommon around tuner and shieldingsections even in new sets.Repairs to TVs and monitors should only be attempted by persons who are fully aware of working safely with high voltages. Monitors and TVs can produce very high, lethal voltages up to 33,000 volts. There are mains voltages inside the cabinet and usually also around 130V DC on the chassis also. If you do go inside, beware: line voltage (on large caps) and high voltage(on CRT) for long after the plug is pulled. There is the added danger ofCRT implosion for carelessly dropped tools and often sharp sheetmetalshields which can injure if you should have a reflex reaction upon touchingsomething you should not touch. In inside of a TV or monitor is no placefor the careless or naive. Monitors designed for PCs, workstations, and studio video have manycharacteristics in common. Modern computer monitors share manysimilarities with TVs but the auto-scan and high scan rate deflectioncircuitry and more sophisticated power supplies complicates their servicing.

      VCR repair

      The video cassette recorder is a wonderful example of extremely complexprecision technology that has been made affordable through mass production.In general, it is usually quite reliable. Treat a modern VCR with a bitof respect and it will provide trouble free service for a long time.The electronics in VCR are generally quite reliable and rarely fail. MostVCR problems are mechanical - dirt and dust in the tape path, deterioratedrubber parts, dried lubrication, wear of precision parts including thespinning video heads, and abuse. Many of those problems can berepaired quite easily if you know what you do. While VCRs with new convenience features are constantly introduced, thebasic function of playing a tape has not changed significantly in 25 years.The older VCRs are built much more solidly than the $100 models of today.Even high-end VCRs may be built around a poorly designed transportand flimsy chassis. However, there are still millions of middle age to older VCRs out there whose life could be greatly extended with a little tender loving care.

      CD players

      CD palyers are complicated devices which include lots of sophisticatedelectronics and mechnics. There are may things which can go wrong there.Many common problems with CD players can be corrected without the need for the service manual or the use of sophisticated test equipment.You can often repair a CD player which is faulty due mechanical problem or wring electrical adjustment.While CD players with new convenience features are constantly introduced, the basic function of playing a CD has not changed significantly in 15 years. Working on optical storage equipment entails a number of personal risks: electrical, laser, mechanical, as well as the possibility of irreversible damage to the equipment and loss or corruption of data due to improper repair or adjustment.

      • Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives - This document was developed specifically for the troubleshooting and repair of the CD players in component stereo systems, compact stereos, boomboxes, car units and portables, as well as CDROM drives (including the Sony Playstation). The purpose of this document is to provide enough background on CD technology and troubleshooting guidance so that anyone who is reasonably handy whether a homeowner, experimenter, hobbiest, tinkerer, or engineer, can identify and repair many problems with CD players and possibly laserdisc players, CDROM drives, and optical storage drives as well.    Rate this link
      • Notes on the Troubleshooting and Repair of Optical Disc Players and Optical Data Storage Drives - While compact disc (CD) players and CDROM drives account for the vast majority of optical disc platforms in the known universe, there are other types in use for both entertainment and data storage applications. These all use optical technology very similar to that of the compact disc and CDROM.    Rate this link


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