Hardware Reference
In-Depth Information
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
Figure 20.4
). 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.
The ESD kits, as well as all the other tools and much more, are available from a variety of tool
vendors. Specialized Products Company (
www.specialized.net
) and Stanley Supply & Services
(
www.stanleysupplyservices.com
)
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.
Test Equipment
In some cases, you must use specialized devices to test a system board or component. This test
equipment is not expensive or difficult to use, but it can add much to your troubleshooting abilities.
