Upgrading And Repairing PCs 21st Edition: PC Diagnostics


From a personal safety point of view, there really isn’t that much danger in working on a PC. Even if it is open with the power on, a PC runs on only 3.3, 5, or 12 volts, meaning no dangerous, life-threatening voltages are present. However, dangerous voltages do exist inside the power supply and CRT monitor. Most power supplies have 400 volts present at some points internally, and color displays have between 50,000 and 100,000 volts on the CRT! Normally, I treat the power supply and monitor as components that are replaced and not repaired, and I do not recommend you open either of them unless you really know what you are doing around high voltages.

Before working on a PC, you should unplug it from the wall. This is not really to protect you so much as it is to protect the system. A modern ATX form factor system is always partially running—that is, as long as the system is plugged in. So, even if it is off, standby voltages are present. To prevent damage to the motherboard, video card, and other cards, the system should be completely unplugged. If you accidentally turn the system all the way on, and plug in or remove a card, you can fry the card or motherboard.

ESD protection is another issue. While working on a PC, you should wear an ESD wrist strap that is clipped to the chassis of the machine (see the image below). This ensures that you and the system remain at the same electrical potential and prevents static electricity from damaging the system as you touch it. Some people feel that the system should be plugged in to provide an earth ground. That is not a good idea at all, as I previously mentioned. No “earth” ground is necessary; all that is important is that you and the system remain at the same electrical potential, which is accomplished via the strap. Another issue for personal safety is the use of a commercially available wrist strap, rather than making your own. Commercially made wrist straps feature an internal 1-megohm resistor designed to protect you. The resistor ensures that you are not the best path to ground should you touch any “hot” wire.

When you remove components from the system, they should be placed on a special conductive antistatic mat, which is also a part of any good ESD protection kit. The mat is also connected via a wire and clip to the system chassis. Any components removed from the system, especially items such as the processor, the motherboard, adapter cards, disk drives, and so on, should be placed on the mat. The connection between you, the mat, and the chassis will prevent any static discharges from damaging the components.

Note: It is possible (but not recommended) to work without an ESD protection kit if you’re disciplined and careful about working on systems. If you don’t have an ESD kit available, you can discharge yourself by touching any exposed metal on the chassis or case.

A typical ESD wrist strap clipped to a nonpainted surface in the case chassis.A typical ESD wrist strap clipped to a nonpainted surface in the case chassis.

The ESD kits, as well as all the other tools and much more, are available from a variety of tool vendors. Specialized Products Company and Stanley Supply & Services are two of the most popular vendors of computer and electronic tools and service equipment. Their catalogs show an extensive selection of very high-quality tools. With a simple set of hand tools, you will be equipped for nearly every PC repair or installation situation. The total cost of these tools should be less than $150, which is not much considering the capabilities they provide.

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