tempus fugit wrote:

Hey all;

A friend handed me her dead computer to see if I could get it up and
running. When you turn it on, nothing happens. No lights, no fans, nothing.
So, I figure it's either the power supply or the motherboard (at least).

I want to test the PS first, before just replacing it. It is an ATX 300w
supply. I connected an 8 ohm 10W resistor from red (+5v) to black (ground)
and turned it on, but nothing happened. I then turned it on and shorted the
green wire to ground, but still nothing. Can I assume the PS is dead, or is
there something else I should be doing?

Thanks



You can not just short the +5 to ground through a resistor on an ATX
supply. There is a line on the ATX connector to the motherboard that
must receive a signal before the PS will supply full power. what you
can do is disconnect the PS from the motherboard and jumper the green
wire to a ground (black) wire. The PS should now come on and you should
be able to read voltages across the outputs.

It could be anything. On the ATX motherboards, there is a constant
voltage applied to the motherboard. when you press the power switch,
the motherboard will do a series of tests. If the tests fail, no power
will be supplied to the motherboard. If the tests pass, then power will
be supplied and the system powers up.

There are many factors that will prevent a system from powering up
nowdays... Some won't power up if there is no signal received from the
CPU fan.

Other things to check:
make sure all memory is seated in the slots correctly
make sure that the motherboard isn't grounded against the case
make sure all connectors are plugged into the motherboard properly
I have seen a hard drive prevent a system from powering up, so check
connections there, too
even a PCI (or AGP) card loose will prevent it from powering up