Re: ALPHA 255, in the intensive care unit
From: David Mathog (mathog_at_caltech.edu)
Date: 10/27/04
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Date: Wed, 27 Oct 2004 09:11:24 -0700
Miguel Angel Usón Finkenzeller wrote:
>
> The famous 2.2 microFarad capacitor next to the mouse and keyboard outlets
> seems allright,
Tested or just visual inspection?
> the power supply puts out the expected +-12, +5 and 3.3
> volts, all the connectors a were and are again firmly attached, and yet...
I've recently had a series of failures on Athlon systems that were very
similar to this. Each power supply seemed ok, but when it was swapped
out with a new unit, the systems stopped crashing. Apparently
some power supplies can fail by passing too much noise or just
glitching from time to time, but these always test at the correct
voltage with a voltmeter (or the system's own sensors, if these are
present.) Admittedly this is a bit unusual, more typically power
supplies just die (sometimes spectacularly). In any case, the power
supply is far and away the most likely component to fail in a way
that would produce these sorts of symptoms. (The disk is probably
more likely to fail but VMS is usually pretty clear about that
and it shows up in the error logs - power supply failures just
crash the system instantly.)
>
> One thing I find strange is that the CPU cooling fan receives only 7.0
> volts. Is that what it should be? As said, the 12v reach the motherboard.
Your voltmeter may be confused trying to measure the DC voltage across
the running fan motor. Does the fan appear to be spinning at a normal
speed? If you're concerned try replacing the fan (fans are cheap).
Also, you should check that the heat sink on the CPU isn't packed up
with dust. I'm not familiar with the heat sink in a 255 but sometimes
one must remove the fan on top to get a good look at the heat sink.
>
> Any hints are appreciated.
It doesn't sound too much like a heat problem if the system
crashes quickly from a cold start. But you didn't say that
exactly, only that it it crashes on restart, and the system
may have been (too) hot at the time. Take off the top of the
case, aim a big floor fan into it, turn the system off
and let it cool down for 15 minutes. Then start it up with
the case still open and the external fan running and see if runs
without crashing. Caveat: what's the ambient room temperature?
Caveat 2: don't plug the floor fan into the same circuit as the computer!
Another possibility - noise or spikes through the power lines.
You're at a university and who knows what hideous equipment is
plugged in nearby. Who knows when said equipment may be running
or not. Try plugging the Alpha into an uninterruptible
power supply or some other device that will feed it clean power.
If that isn't available try it elsewhere on campus or at home
where the power is less likely to be contaminated by heavy
electrical equipment.
Regards,
David Mathog
mathog@caltech.edu
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