psu shorted motherboard

[tilopa]

I swaped out my PSU from a system that had a P4 mother board into a
system that had a Athlon XP motherboard. I connected both the 20-pin
and 4-pin connectors to the MB. When I plugged in the system and then
hit the PW switch nothing happened, no fans, nothing. The light from
the NIC card did come on showing there was some power coming to the
board. A few seconds later the light began to fade and then there was
this loud crack and spark and fizzle followed by that electrical burn
smell. I unplugged the PSU immediately. I was sure I fried my MB but
when I put the old PSU back in the system it powered up, but I had not
video, when I replaced the video card everything powered up and the
system booted fine. Appearently the video card (AGP) was the only thing
damaged. But I am at a loss for what happened, why would a bad PSU do
that, if in fact the PSU is the problem. I have a multimeter and now
how to test my PSU with the PSU running current to the board but I
obviously do not want to connect that PSU to my board. Is there a way
to test the PSU without connecting it to the MB. Does anyone have any
ideas why this occurred and what the problem could be?

 

[MJP]

I swaped out my PSU from a system that had a P4 mother board into a
system that had a Athlon XP motherboard. I connected both the 20-pin
and 4-pin connectors to the MB. When I plugged in the system and then
hit the PW switch nothing happened, no fans, nothing. The light from
the NIC card did come on showing there was some power coming to the
board. A few seconds later the light began to fade and then there was
this loud crack and spark and fizzle followed by that electrical burn
smell. I unplugged the PSU immediately. I was sure I fried my MB but
when I put the old PSU back in the system it powered up, but I had not
video, when I replaced the video card everything powered up and the
system booted fine. Appearently the video card (AGP) was the only thing
damaged. But I am at a loss for what happened, why would a bad PSU do
that, if in fact the PSU is the problem. I have a multimeter and now
how to test my PSU with the PSU running current to the board but I
obviously do not want to connect that PSU to my board. Is there a way
to test the PSU without connecting it to the MB.

Look here for details of how to do it and a diagram
http://www.duxcw.com/faq/ps/ps4.htm

MJP

 

[kony]

I swaped out my PSU from a system that had a P4 mother board into a
system that had a Athlon XP motherboard. I connected both the 20-pin
and 4-pin connectors to the MB. When I plugged in the system and then
hit the PW switch nothing happened, no fans, nothing. The light from
the NIC card did come on showing there was some power coming to the
board. A few seconds later the light began to fade and then there was
this loud crack and spark and fizzle followed by that electrical burn
smell. I unplugged the PSU immediately. I was sure I fried my MB but
when I put the old PSU back in the system it powered up, but I had not
video, when I replaced the video card everything powered up and the
system booted fine. Appearently the video card (AGP) was the only thing
damaged. But I am at a loss for what happened, why would a bad PSU do
that, if in fact the PSU is the problem. I have a multimeter and now
how to test my PSU with the PSU running current to the board but I
obviously do not want to connect that PSU to my board. Is there a way
to test the PSU without connecting it to the MB. Does anyone have any
ideas why this occurred and what the problem could be?

I would wonder if, while installing the PSU or other system
changes, the video card might've been dislogded somehow and
wasn't seated properly in the slot, perhaps in combination
with mangled slot contacts or something similar since this
isn't a common problem.

A basic test for the PSU would be to short the PS-ON line
(pin 14, green wire) to ground and put a load on the other
rails- 3.3V, 5V, 12, (and 12V2 if it's a split-rail psu,
12V2 being the 4-pin connector). The larger the load the
better, up to the expected true capacity of the psu. At a
minimum you should put at least 2A on each rail.

 

[kony]

...The larger the load the
better, up to the expected true capacity of the psu. At a
minimum you should put at least 2A on each rail.

By the above I meant on the 3.3V, 5V, and 12V rail(s), not
on those rails not even (necessarily) spec'd as capable of
2A, not on the 5VSB, -12V, -5V,

 

[tilopa]

Thanks Kony and MJP for the replys and good suggestions. I will try
that and see if my PSU is bad.