Al wrote:

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.)

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.

The Power_Good_ signal is an output, not an input, but the Power_On
signal is an input, and if the Gateway/Newton is wired like standard
ATX it's pin 14 (green wire), activated by grounding it.

I'd first work on getting the 5V on pin 9 to work. It runs from either
the main power oscillator or has its own oscillator.