VAXstation/MicroVAX 2000 CPU/FPU overheating?

[Dave Dunfield]

> > I have a feeling the FPU is knackered - it seems to be generating more
> > heat than the CPU (hard to tell as they are mounted side by side and
> > there is a fair bit of heat trasnfer through the board). Unlikely I
> > can find a replacement --- Anyone got a VAXstation 2000 or MicroVAX 2000
> > thats dead for some other reason?
> > 
> > Odd thing is that everything seems to work - if I place a small fan
> > to keep the CPU & FPU cooled to "just hot", it settles back down and
> > all seems to work correctly. All self-tests pass (including FPU). It
> > appears it would run indefinately in this state, but it's obviously
> > not healthy. It seems unlikely that there would be an internal chip
> > failure that would cause it to eat this much power and still perform
> > it's intended function.
> 
> This may be a stupid question but bear with me.  Is the surface of the 
> FPU chip getting hotter than the heatsink sitting on it?

I don't believe so, although I haven't gone to great lengths to make
sure - the heat-sink covers most of the chip. The heatsink itself is
firmly attached and gets *plenty* hot (I've been mostly toasting my
fingers on the heatsink, not the chip itself). Sticking a bigger heatsink
to the integral one with thermal compound also works as a temporary
way to keep the chip cooler, which leads me to believe that the heat
conduction between chip and heatsink is OK.  (but that isn't a fix - just
a way to confirm that the cause of death is thermal ... I'm still trying
to find a reason for all this heat).

Dave

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dave06a (at)    Dave Dunfield
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