Hardware Reference
In-Depth Information
symptoms point right to the power supply as a possible cause:
• Completely dead (no fan, no cursor)
• Smoke
• Blown circuit breakers
If you suspect a power supply problem, some of the simple measurements and the more sophisticated
tests outlined in this section can help you determine whether the power supply is at fault. Because
these measurements might not detect some intermittent failures, you might have to use a spare power
supply for a long-term evaluation. If the symptoms and problems disappear when a known-good spare
unit is installed, you have found the source of your problem.
The following is a simple flowchart to help you zero in on common power supply-related problems:
1.
Check the AC power input. Make sure the cord is firmly seated in the wall socket and in the
power supply socket. Try a different cord.
2.
Check the DC power connections. Make sure the motherboard and disk drive power connectors
are firmly seated and making good contact. Check for loose screws.
3.
Check the DC power output. Use a digital multimeter to check for proper voltages. If it's below
spec, replace the power supply.
4.
Check the installed peripherals. Remove all boards and drives and retest the system. If it
works, add items back in one at a time until the system fails again. The last item added before
the failure returns is likely defective.
Many types of symptoms can indicate problems with the power supply. Because the power supply
literally powers everything else in the system, everything from disk drive problems to memory
problems to motherboard problems can often be traced back to the power supply as the root cause.
Overloaded Power Supplies
A weak or inadequate power supply can put a damper on your ideas for system expansion. Some
systems are designed with beefy power supplies, as if to anticipate a great deal of system add-ons
and expansion components. Most desktop or tower systems are built in this manner. Some systems
have inadequate power supplies from the start, however, and can't adequately service the power-
hungry options you might want to add.
The wattage rating can sometimes be misleading. Not all 500-watt supplies are created the same.
People familiar with high-end audio systems know that some watts are better than others. This is true
for power supplies, too. Cheap power supplies might in fact put out the rated power, but at what
temperature? Many cheap power supplies are rated at ridiculously low temperatures that will never
be encountered in actual use. As the temperature goes up, the power output capability goes down,
meaning that in some cases these supplies will only be capable of 50% less than their rating under
normal use.
Also, what about noise and distortion? Some of the supplies are under-engineered to just barely meet
their specifications, whereas others might greatly exceed their specifications. Many of the cheaper
supplies provide noisy or unstable power, which can cause numerous problems with the system.
Another problem with under-engineered power supplies is that they can run hot and force the system
to do so as well. The repeated heating and cooling of solid-state components eventually causes a
computer system to fail, and engineering principles dictate that the hotter a PC's temperature, the
