All,
I'm wondering if someone can confirm my diagnosis for a problem with
my VAX 4000-300. One day, after it had been running for the better part
of a week, I found it unresponsive with only the AC light glowing. I
suspected an overheat problem, but the overtemp light wasn't on.
Nonetheless, I shut the machine down, left it for a while and came
back. It started up again, booted into VMS and seemed fine. I let it
run for a half-hour or so, then shut it down normally. That was two
days ago.
I just tried to power it up again to do some work, and the power-on
tests fail about halfway through (but never in the same spot, so I don't
think it's actually a power-on test failure). The machine goes to the
same state each time: just the AC lamp glowing. I even have the fans on
high (and that's noisy), but no go.
I figure it's time to replace the power supply unit (or refurbish it,
but replacements are still relatively cheap). Any other thoughts?
Disclaimer : I have never worked on this machine.
Do you have/can you get a pinout of the PSU output connector? If so, I'd
check the PSU output voltages (particularly when the machine has failed),
and look at the state of any power_good / powe_fail lines. If you have a
'cope, look for excessive ripple on the supply outputs too.
My guess, if it is a PSU problem, is that this is a dried-up (high ESR)
electrolytic cacpaitor somewhere. The problem is finding it...
-tony