VAXstation/MicroVAX 2000 CPU/FPU overheating? - test-drb@ccmp.vtda.org

29 Feb 2008

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Subject: Re: VAXstation/MicroVAX 2000 CPU/FPU overheating?
   From: ard at p850ug1.demon.co.uk (Tony Duell)
   Date: Sat, 01 Mar 2008 00:46:23 +0000 (GMT)
     To: cctalk at classiccmp.org

 At 9:26 -0600 2/29/08, Dave wrote:
 Yes, I'm wondering if it's something like
that, however how likely is it
that both devices would experience the same fairly-uncommon failure mode
at the same time?  
 I'm chiming in very late and probably not very helpfully, but is 
 there any way a decoupling cap in the vicinity of the FPU/CPU could 
 either load them or generate heat itself by beginning to short to 
 ground? My only VAX (4000VLC) had a fault like that in the reset  
Interesting idea.... I've worked with chips that had connectiosn for 
decoupling capacitors for particualr secitons in the chip (the most 
ovious being the Transputer which needs a 1uF capacitor between 2 of its 
pins to decouple the clock multiplier PLL). In general, these components 
are not conencted to a power line or ground other than through the chip.

I have no idea if the VAX 2000 chips are like this, but if they are, then 
a leak in one of those cpacitors would certainly cause thigns to run hot. 
The 78032 chip is 1986 surface mount (gull wing) tech.  No cap on the 
chip, same for the FPU.  At the time it was pushing the limit for NMOS
for power and density, they plain just run hot.

If you don't like them that hot adding another set of fins to radiate 
that heat helps.

Allison

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 -tony 