Diagnose and Repair Modern Electronics: A DIY Guide: Introduction and Article Index

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INTRODUCTION

The focus of this guide is on today's electronics, most of which are digital in nature, and the kinds of problems you're most likely to encounter. It might seem like there isn't that much one can service in modern digital gear, compared to the older analog circuitry. Dense boards populated by rows of chips with leads too close together even to poke at with a test probe don't seem like good repair candidates, do they? Luckily, those areas aren't where most failures occur, and there's still plenty of accessible circuitry to work on! In fact, some common problems in today's gear were rare or nonexistent in earlier technology, and they're quite reparable.

Exotic and very obsolete components and their associated products aren't covered in this guide. Electron tubes, once the mainstay of all electronics, are pretty much gone, so we won't spend time on their peculiarities and specific troubleshooting methods. If you want to repair tube-type guitar amplifiers, you can find books dedicated to them. Similarly, we won't be discussing microwave ovens, which also have tubes, or transmitting amplifiers of the sort used by amateur radio operators. Nor will we take more than a passing glance at cathode ray tube (CRT, or picture tube)- based TVs and monitors. The CRT had a good long run, from the 1940s until just a few years ago, but it's a dead technology, thoroughly supplanted by flat-panel displays.

Servicing CRT sets is rather dangerous, so please find a guide devoted to them if you have an interest in, say, restoring antique TVs. What's covered here is relevant but not comprehensive enough regarding that topic to keep you safe around those high voltage beasts.

Some obsolete technology is still in common use and may remain so for years to come, so we'll explore it. Tape-based video recording continues to be used in some digital camcorders. VCRs, which are rapidly disappearing as high-definition TV (HDTV) obsoletes them, may be the only key to recovery of precious home movies yet to be transferred to digital media. Serious audio devotees treasure their analog tape recorders and turntables and will never replace them with CD or MP3 players.

We won't spend much time on the old formats, but the troubleshooting techniques covered here are applicable to their repair.

Most of today's digital equipment still contains analog circuitry for audio or video output, microphone input, voltage regulation and such. Home theater receivers use analog amplifier stages, and many have old-fashioned, linear power supplies as well, because they're electrically quieter than newer, pulse-driven designs. In fact, the best audiophile-grade stereo gear is pretty much all analog and will likely remain that way. Even digital radio and TV receivers use analog stages to amplify and separate incoming signals before digital decoders extract the data. So, troubleshooting techniques specific to analog circuitry are far from antiquated; they continue to be relevant in our digital era.

In this guide, it’s assumed that you have probably opened an electronic device at one time or another and checked a fuse. Perhaps you know a resistor when you see one, and maybe you've even soldered or done some basic troubleshooting. Still, we're going to start from the top, ensuring you're a sound swimmer before diving into the deep end. And dive we will! Beginning with a look at the tools you'll need, we'll explore setting up your home workshop. We'll discuss the best types of workbenches and lamps, and where to put your gear and tools. We'll take a close look at the most useful test instruments, where to find bargains on them, and how to operate them.

Getting good with an oscilloscope is key to being a crack shot tech, so we'll explore a scope's operation in detail, button by button.

Using other test equipment like digital voltmeters and ohmmeters is also crucial to effective repair. We'll focus on commonly available test gear, without spending significant effort on very expensive, exotic instruments you're never likely to own.

We'll examine how to take a product apart, figure out what's wrong with it, replace parts and close it back up again. Finally, we'll look at tips and tricks for specific devices, from optical disc players to video recorders and receivers. Here's a quick breakdown of what's in each section.

  1. Section 1, Introducing DIY Fixing: Why repair things? Environmental and economic factors, learning, fun, preserving rare and obsolete technology, potential profit. When is a product worth repairing, and when is it better to scrap for parts?
  2. Section 2, "Setting Up Shop: Tools of the Trade": Necessary items, from hand tools to test instruments, and how to buy them. Must- haves, nice-to-haves, and expensive goodies to dream about. How to select a workbench and set it up, and where to put it.
  3. Section 3, Electronics Lab Safety: How to avoid getting hurt while servicing electronics: electrical and physical hazards, eye and ear protection. How not to damage the device you're repairing: causing electrical and physical damage. Ensuring user safety after product repair.
  4. Section 4, "The Philosophy of DIY Troubleshooting": General troubleshooting principles: why things work, why they stop. Common mistakes and how to avoid them. Organization of modern devices: microprocessor brains, nervous system, muscles and senses. The "art" side of electronics: manufacturer-specific quirks and issues. What fails most often and why. Failure history and how it helps diagnose problems. • Preliminary diagnosis based on symptom analysis: dead, comatose and nearly working. Case histories.
  5. Section 5, "Important Terms, Concepts and Building Blocks": Electrical units: volts, amps, resistance, capacitance, and so on. Circuit concepts: how parts connect and how current moves through them. Series and parallel. Signal concepts: how changes in voltage represent information. Waveforms. Analog and digital representation. Building blocks: common circuits used in many products. Amplifiers, oscillators, frequency synthesizers and power supplies.
  6. Section 6, "Using Test Equipment": Digital multimeter: measuring voltage, current and resistance. Oscilloscope: detailed, button-by-button operation, including delayed sweep measurements. AC and DC signal components, rolloff and other issues affecting measurement strategy. Soldering and desoldering techniques. Bench power supply: voltage and current considerations, DC plug polarity. Transistor tester. Capacitance meter. Signal generator. Frequency counter. Analog meter: when to use it, interpreting the wiggling meter needle, tests not possible with a digital instrument. Contact cleaner spray: what to use it on, what not to. Component cooler spray: solving thermal intermittents, considerations for safe use.
  7. Section 7, "Basics of Components": Common parts: capacitors, clock oscillators, crystals, diodes, fuses, inductors and transformers, integrated circuits, op-amps, resistors, potentiometers, relays, switches, transistors, voltage regulators and zeners. Varieties of each type of part. Symbols, markings and photos. Uses: what components do in circuits. What kills them. How to test them out of circuit.
  8. Section 8, "Diagrams and Schematics": Block, schematic and pictorial diagrams. Learning to read diagrams like a story: signal flow, organization in stages. Symbols and call numbers. Good, average and bad diagrams. Part-by-part analysis of individual stages and their functions. Amplifier example. Organization of larger structures. Switching power supply example. Practicing reading: looking for stages and structures in radios and DVD players. Working without a diagram. Case history of troubleshooting an LCD TV without a schematic.
  9. Section 9, "Opening, Disassembling, Getting Inside": Separating case halves: hidden snaps. Disconnecting ribbon cables. Layers: disassembling in order, use of digital photos and nested cups. Disassembly tips for common products: receivers, VCRs, CD/DVD players, flat-panel TVs, turntables, video projectors, MP3 players, PDAs, cell phones, camcorders, digital cameras and laptop computers.
  10. Section 10, "What is That: Recognizing Major Features": What various sections of circuitry look like: descriptions and photos. Recognizing sections from components specific to their functions: inductors, power transistors, and so on. Power supplies: linear and switching. Backlight inverters. Signal processing areas, analog and digital. Digital control sections. Output stages: discrete transistors and integrated modules. Mechanisms: video head drum, capstan motor, laser optical head and DLP color wheel. Danger points.
  11. Section 11, "Signal Tracing and Diagnosis": Where to begin, based on observed symptoms. Dead, comatose or crazy, alive and awake but not quite kicking. Intermittents: thermal and mechanical, bad solder joints, board cracks, positional • and vibration-sensitive. Working forward or backward through stages: when each technique is appropriate. Stages, test points and making sure you're in the right place. Zeroing in on bad components. Desperate measures: shotgunning, current blasting and LAP method.
  12. Section 12, "Circuit Boards and Replacing Components": Desoldering through-hole and surface-mount components. Choosing replacement parts: new, from your stash and from parts machines. Substituting similar parts when you can't get the exact replacement: vital characteristics that must be matched or exceeded, and allowable differences in capacitors, diodes, resistors, transistors and zeners. Installing new parts: through-hole and surface-mount, mounting power transistors. Finding components: standardized, proprietary, local, mail-order, new and surplus. Saving damaged boards: bridging broken conductors and bad layer interconnects. Reflowing solder on high-density integrated circuit chips.
  13. Section 13, "Reverse-Order Reassembly": Common reassembly errors. Ensuring good ground connections on boards and chassis. Lead dress: placement of wires and cables, physical and thermal risks, electromagnetic interference. Reconnecting ribbon cables. Repairing damaged ribbon sockets. Reversing layer and cup order. Rejoining plastic snaps. Reinserting screws: tension and correct placement. Final test.
  14. Section 14, "Tips and Tricks for Specific Products": How they work, what can go wrong, when repair is worth doing, dangers within, and how to fix them. Switching power supplies, receivers, disc players and recorders, flat-panel displays, hard drives, laptop computers, MP3 players, VCRs, camcorders and video projectors. Whether or not you've already had your hands inside some electronic devices, this guide will guide you from the "maybe it's the fuse" level to the "ah, the biasing diode on the output stage is open" point. It will help hone your sleuthing skills with logic and a solid foundation in how things work, until you feel like an ace detective of electrons. At the very least, it'll leave you fascinated with everything that goes on inside your favorite gadgets and eager to tackle everything that comes your way.
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