Lis chaque section en anglais. Le resume en francais ("En bref") est juste un filet de securite : essaie de comprendre en anglais d'abord.
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Technicians do not disassemble a whole computer very often. It is usually done to find a hard-to-diagnose problem, or to learn. One reason for full disassembly is an equipment grounding problem: the motherboard or an adapter is installed incorrectly and a trace (a thin metal line on the board) touches the case frame, causing that part (and maybe others) to stop working.
The electronic parts inside a computer (motherboard, adapters, memory) can be damaged by ESD (electrostatic discharge) - a small static electricity shock. A person only feels a shock at about 3,000 volts, but a tiny shock of just 30 volts can already damage a computer chip. Chips and memory modules are the parts most at risk. The damage from ESD is often invisible and cumulative: a part can survive the first small shock but be weakened, and eventually fail later from build-up damage. There is no way to undo ESD damage once it happens.
Low humidity makes ESD worse (dry air lets static build up); but too much humidity is also bad for electronics. Technicians try to keep humidity between 45% and 55% when possible.
The main way to prevent ESD is an antistatic wrist strap (also called an ESD strap): one end goes around the technician's wrist, the other end clips to a grounding post or bare metal part of the case (or the power supply). This keeps the technician and the computer at the same electrical potential, so no static discharge happens between them. Antistatic gloves work better than a wrist strap on laptops, which often have no good place to attach a strap.
Do NOT wear an antistatic wrist strap when working inside a power supply or a CRT (old tube) monitor - these contain dangerously high voltage, and a technician should not be inside them without special training anyway.
If a wrist strap is not available, self-grounding helps: after opening the case, keep one bare arm/elbow resting on an unpainted metal part (such as the power supply) while removing parts with your other hand. This is not as safe as a proper wrist strap, but it reduces the risk. It is also wise to unplug the power cord completely, since a power supply still sends a small amount of standby power to the motherboard even when the computer is 'off'.
Antistatic bags are used to store spare adapters and motherboards when not in use (though they lose effectiveness after a few years). ESD mats can be placed under a computer being repaired, sometimes with a snap to connect the wrist strap.
As little as 30 volts (much less than the ~3,000 volts a human can feel).
Use an antistatic wrist strap.
Between 45% and 55%.
Inside a power supply or a CRT monitor - both hold dangerously high voltage.
Keep a bare arm/elbow resting on an unpainted metal part (like the power supply) while removing parts.
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EMI (electromagnetic interference) is electrical noise produced by devices such as motors, vacuum cleaners, pencil sharpeners, air conditioners, or fluorescent lighting. Devices outside the computer case (including speakers) usually cause more EMI problems than the computer itself. EMI can also come through the power lines, and it can even affect data stored on a hard drive.
RFI (radio frequency interference) is a specific kind of EMI, in the radio-frequency range. EMI/RFI problems are notoriously hard to trace to their source. If a computer has an intermittent (comes and goes) problem, check nearby electrical devices as a possible source. Moving the computer, or plugging it into a different wall outlet or a completely different circuit, can help identify or fix the problem.
Covering empty expansion slots with slot covers reduces EMI/RFI, keeps dust out, and improves airflow within the case.
Electrical noise from nearby devices that can cause problems in a computer.
Move the computer or use a different power outlet/circuit; cover empty expansion slots.
It reduces EMI/RFI and improves airflow inside the case.
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Tools are used to remove and replace FRUs (field replaceable units) - the parts of a computer or device meant to be swapped out, like the power supply or motherboard.
Most repairs only need a few basic tools: small and medium flat-tipped screwdrivers, Phillips screwdrivers (#0, #1, #2), 1/4-inch and 3/16-inch hex nut drivers, small diagonal cutters (great for removing tie wraps without cutting cables), and needle-nose pliers (for straightening bent pins on cables/connectors, and many other small tasks).
Avoid magnetic screwdrivers when possible: even though they are convenient for picking up dropped screws, a magnetic field can affect (damage) memory. If a screw falls somewhere unreachable (like under the motherboard), try tilting the computer in different directions until the screw comes loose instead.