"Al" wrote in message
. ..
Hi. This is on a Gateway Essential, 950 Mhz Celeron, FlexATX, mfg date in
fall of '91. The Power Supply is SFX, Gateway's part# is 6500545, 90W.
(AKA Newton NPS-145PB-117 A Rev 03).

The computer would start but then go only into standby mode (with the
power indicator being always yellow, never green). After a few days of
that behavior, it would then start only for a moment, and only with a few
spins of the ps fan (there is no CPU fan). Pushing the start button again
would have no effect - unless I removed the power cord and let it sit for
a minute or two. Then I'd replug and the pattern would repeat, with only
a momentary start for the first button press.

With an analog voltmeter, I would see 1V for that brief moment, on
POWER_GOOD (pin 8). (I got the exact same result measuring between pins 3
and 9, which should have given 5V.) When I removed all drives and tried
again, I got the same behavior.

So, I took out and opened up the PSU. There was some dust, which I blew
out. (Nothing looked burnt, that I could see.) But thereafter, the
computer behaved differently: when I merely plugged the power cord in,
I'd get the momentary light and ps fan spinning. It didn't need me to
actually push the power button anymore. Next, to see if the power on
switch might be shorted, I removed its leads from the MB - but that
didn't change anything.

It seems to me that maybe the CPU is not getting a good signal on
POWER_GOOD, and so shuts down the PSU. Or could it be that the CPU, the
MB or some other thing is bad, not the power supply? The more I research
on this, the more it goes round and round.

I'd rather not waste $40-50 on trying a new PSU, not to mention the week
or more it would take to be shipped to me, if it's not likely to be a PSU
failure. How can I tell if the PSU is bad or not? Thanks.

Oh, and one more thing: weird behavior showed up in the last few weeks,
like the mouse and/or keyboard or even drives not showing up on POST.
This msg would also sometimes be given by Windows: "An unknown device has
exceeded the current limits of its hub port". And a USB attachment for an
MP3 player had been added after Christmas. But the "current exceeded" msg
still sometimes appeared, even after the MP3 attachment had been removed.

Check the 5V Standby output of the PSU on pin 9 of the connector (that will
be the green wire) with the PSU unplugged from the motherboard. If that
voltage is not present, your power supply is bad. That's the power to the
motherboard that powers the Wake-On-xxx circuitry in the computer. If it's
not there, there's no way for the motherboard to tell the PSU to go to full
power.

If that voltage is present, use a pice of hookup wire or a paper clip bent
into a "U" shape to temporarily short pin 14 on the connector to either
adjacent pin (pin 13 or pin 15). That simulates the motherboard signal to
go full power. If that desn't turn the power supply on, then the PSU is
bad.

If the 5V Standby voltage is present, but the motherboard doesn't turn the
PSU on, then the motherboard is likely bad. Don't forget the power switch
on the front of the computer. Be sure to check that with your ohmmeter.

--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!