Subject: DEC 3000/M400 cooling
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: port-alpha
Date: 07/16/2004 00:01:50
I have a

DEC 3000 - M400, 133MHz
8192 byte page size, 1 processor.
total memory = 192 MB

that's running NetBSD fairly happily.  However, I had it sitting idle
for some months, and recently brought it back to life.  It now seems to
suffer from some kind of thermal problem: after running for something
like ten minutes, it locks up hard.  Power-cycling it brings it back,
for a few more minutes - or more, if I leave it off for a longer time.

The reason I'm sure it's thermal is that I opened it up and took
everything out of the case, and have it sitting propped up on edge on
the desk, with fans placed to blow on strategic areas.  Under this
arrangement, it's stayed up for something over twenty hours, whereas
before its uptime was measured in minutes and never hit half an hour.

The reason I'm writing is that even with fans blowing on it, two areas
are hot enough that they'd disturb me except that the machine is
obviously happy with them that way.

Holding the motherboard with the back-panel connectors facing you,
component side up, the most obvious heat generator is of course the
CPU.  But looking to the left of the CPU, there are some smaller chips,
then two big chips, then a bunch of some 15 to 20 smaller chips.  This
latter bunch run hot enough to worry me.  And on the motherboard,
underneath the daughterboard with all the back-panel connectors,
approximately under the area behind the ISDN/Ethernet connectors,
something is getting very hot - the back of the board (the only
accessible part) gets hot enough that I could probably injure myself if
I left my hand on it very long - despite my having placed a fan
specifically to cool that area.

Is this normal?  It certainly appears that the built-in cooling in the
case wasn't keeping it cool enough, despite there being nothing
obviously wrong with it (I looked for clogged dust grilles and such).
Also, it used to work fine when all put back together in the case.

If this does indicate something wrong, is it likely to be fixable?

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