Knowledgebase : Hardware > Other
Power System
Posted by Administrator on 22 January 2016 12:13 pm

Troubleshooting the Power System
The power supply is one of the most important elements of
a good, working PC. Devices such as CPUs, RAM, and

peripheral devices operate with small voltages to conserve power
and lessen the amount of operating heat. Voltages supplied
to these devices must be within a tight tolerance (usually
five percent), regardless of the load, or components can be
damaged or destroyed. A five percent difference for a fivevolt

device is only .25 volts (VDC). It’s recommended that
your power supply have a wide voltage input range to cover
line brownouts (power loss) or surges and that it have a
large enough total output wattage to cover all PC devices.
Earlier systems with 150-watt power supplies were adequate
because the user had a hard drive and floppy drive. Later,
he or she may have added a CD-ROM drive. Newer systems
have more peripherals plugged into USB, serial, parallel, and
Firewire ports. There are also more adapter cards for highend

video and audio—some with their own processors. All
of these components require more power and generate more
The cooling fan for the power supply should be designed for
the case, be large enough to dissipate the inside heat, and be
installed correctly. Some PCs have cooling systems installed
because of dual processors and multiple peripheral devices.
Typically, for each 10 degrees the temperature is reduced, the
life of your PC doubles.
Some power supply problems are obvious, such as fan noise
or excessive heat from the power supply itself. But power
supply problems can be hidden sometimes, or at least not
obvious, as you troubleshoot software and hardware. Below,
we’ll start with one of the easier problems to spot, no power.

PC Has No Power
Are there any burnt parts or odors? Look for any damaged
cables, cords, or components that might have smoke or burn
residue. Smelling for a particular component may be difficult;
sometimes the smell is located within the motherboard electronics.

Normally, because of the danger of a stored electrical0
charge, the relatively small expense, and the necessity of
stable voltage, power supplies that display a problem are
simply replaced.
Is everything (power cords, cables, etc.) connected
correctly? One of the first steps is to verify that there’s
power at the outlet. Plug in a lamp or radio and make sure
that electricity is still flowing. Maybe a surge has blown a
fuse or tripped the circuit breaker. If you have the PC
plugged into a surge protector, verify that it still outputs
power. Although not seen very often anymore, older AT-style
machines might have a fuse in the back that needs checking.
Change power cords, just to eliminate the remote possibility
of an internal short. Make sure all power and cable connections
are seated.
Are all the switches on? Is there power to the computer?
This was covered somewhat above, but verify that there’s
power. Then verify that switches are on and functioning.
Older AT systems have a switch that’s a true power on/off
switch. The newer ATX-style cases have an on/off switch
connected to the motherboard by a wire from the front panel.
This wire (typically labeled “Remote SW” or “PWR SW”) must
be connected and the switch working before the PC system
board will command the PC to power up (Figure 2). This
arrangement, called system board control, includes sleep
mode for energy conservation and scheduled startup mode.

Remote Switch

One other switch that’s commonly overlooked is the 120V/220V
switch on the back of the power supply. If yours has one,
make sure that it’s set to the correct AC voltage.
Is the cooling fan operating? If it isn’t, turn off


the computer, open the case, and check to see that the power supply
connections are secure. Make sure all the cards are seated in
their slots. The adapter cards slot placements must be verified
because if cards aren’t seated correctly, sometimes a short with
the case may occur. If the fan still isn’t operating and there’s
power present, replace the power supply. Also, replace it if the
power supply is very hot or the fan is very noisy (meaning
impending failure and PC overheating). If you have power and

simply find that the fan isn’t working, some technicians will
replace the fan and then verify all outputs. However, this usually