Power supply problem

[bdljm]

A friend of mine just gave me an old Gateway computer that doesn't work due
to what appears to be a power supply problem. When I push the ON switch,
the light blinks and the PS fan jerks for like half a second, then nothing
at all happens. Now, the strange thing is, the power supply works by itself
if I ground the PS_ON# pin, but doesn't work when connected to the MB.
Ok, so I thought the MB may be defective, but, another PS I have powers up
when connected to the MB, and the Gateway PS works on a differant MB I have.
None of this makes any sense to me, I have checked everything, searched the
Net for info, and can't figure this out.
The computer is a Gateway FLEXATXSTC BRO Essential 700c, the PS is a
NPS-145PB-117 A Rev:03.
Any help at all would be greatly appreciated!

TIA,

Warren

[Arno Wagner]

In comp.sys.ibm.pc.hardware.misc bdljm <blah...@nospam.net> wrote:
> A friend of mine just gave me an old Gateway computer that doesn't work due
> to what appears to be a power supply problem. When I push the ON switch,
> the light blinks and the PS fan jerks for like half a second, then nothing
> at all happens. Now, the strange thing is, the power supply works by itself
> if I ground the PS_ON# pin, but doesn't work when connected to the MB.

Classical problem: The capacitors in the PSU have lost most of their
capacity, thus decreasing the maximum output load of the PSU.
At least it typically is the capacitors. Can also be defective
power semiconductors, but that is rare. so the PSU starts, cannot
get the voltages up within a second or so and then is shut down again
by the short-circuit protection.

Without load the PSU still can get the output voltages to nominal
fast enough. Short-circuit protection has to work this way on
start-up, since in the fist hundred or so miliseconds a PC draws much
more power than normal, so the short-circuit protection is off in
the first second and only starts monitoring the outputs for too low
voltage levels after that.

Some high-quelity PSUs may actually have current monitoring, but
usually it is just output voltage monitoring and overtemperature
monitoring. Works almost as well and is a lot cheaper to do.

> Ok, so I thought the MB may be defective, but, another PS I have powers up
> when connected to the MB, and the Gateway PS works on a differant MB I have.
> None of this makes any sense to me, I have checked everything, searched the
> Net for info, and can't figure this out.

Has been discussed here before, but was maybe not that easy to find.
Have you tried groups.google.com?

> The computer is a Gateway FLEXATXSTC BRO Essential 700c, the PS is a
> NPS-145PB-117 A Rev:03.
> Any help at all would be greatly appreciated!

Just replace the PSU. Nothing else to do without solid electronics
skills.

Arno
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