Hardware Reference
In-Depth Information
•
USB hub, USB/FireWire cable adapters
—These connect multiple external USB
devices.Thecableadaptersandgenderchangersarerecommendedforconnectingdif-
ferent types of USB and FireWire devices.
•
Spare screws, jumpers, standoffs, and so on
—These are handy if you lose any of
these items from the system you are working on.
•
Spare CR-2032 lithium coin cell batteries
—TheseareusedastheCMOSRAMbat-
teries in most systems, so it is a good idea to have a replacement or two on hand. Al-
thoughanumberofCR20xxbatterytypesareavailable,mostsystemsusetheCR2032.
Safety
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
andnotrepaired,andIdonotrecommendyouopeneitherofthemunlessyoureallyknow
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 per-
sonal safety is the use of a commercially available wrist strap, rather than making your
own. Commercially made wrist straps feature an internal 1-meg ohm resistor designed to
protectyou.Theresistorensuresthatyouarenotthebestpathtogroundshouldyoutouch
any “hot” wire.
When you remove components from the system, they should be placed on a special con-
ductive antistatic mat, which is also a part of any good ESD protection kit. The mat is
