Hardware Reference
In-Depth Information
Always be sure you run your computer with the case cover on, especially if you have an
older,loaded system usingpassive heatsinks. Removing the cover inthat situation can ac-
tually cause the system to overheat. With the cover off, the power supply and chassis fans
no longer draw air through the system. Instead, the fans end up cooling only the supply,
and the rest of the system must be cooled by simple convection. Systems that use an act-
ive heatsink on the processor aren't as prone to this type of problem; in fact, the cooler air
from outside the normally closed chassis can help them to run cooler.
In addition, be sure that any empty slot positions have the filler brackets installed. If you
leave these brackets off after removing a card, the resultant hole in the case disrupts the
internal airflow and can cause higher internal temperatures.
Finally, the location of the system can have an effect on cooling. I don't recommend pla-
cing a system on a carpeted floor, as most chassis are designed to draw in air at the bot-
tom of the front bezel, which can easily be blocked or become clogged with carpet fibers.
Another problem is that a system sitting directly on a floor will ingest a large amount of
dust and debris, even more so if the floor is carpeted. If you must place a system on the
floor,whetheritiscarpetedornotIrecommendelevatingitatleastaninchorsoviasome
sort of platform.
If you experience intermittent problems that you suspect are related to overheating, up-
graded chassis fans and/or a higher-capacity replacement power supply are usually the
best cures.
Using Digital Multimeters
One simple test you can perform on a power supply is to check the output voltages. This
shows whether a power supply is operating correctly and whether the output voltages are
withinthecorrecttolerancerange.Notethatyoumustmeasureallvoltageswiththepower
supply connected to a proper load, which usually means testing while the power supply is
still installed in the system and connected to the motherboard and peripheral devices.
Selecting a Meter
You need a simple digital multimeter (DMM) or digital volt-ohm meter (DVOM) to per-
form voltage and resistance checks on electronic circuits (see
Figure 18.38
)
. Only use a
DMM instead of the older needle-type multimeters because the older meters work by in-
jecting 9V into the circuit when measuring resistance, which damages most computer cir-
cuits.
Figure 18.38
A typical DMM.
