VAXstation/MicroVAX 2000 CPU/FPU overheating?

Allison ajp166 at
Fri Feb 29 08:50:52 CST 2008

The same CPU and FPU are sued on the KA630cpu (uVAXII) and in early 
microvax3100s so any of them should compare.

Is it possible that someone has overclocked the that uV2000???

FYI: gate leakage would kill the chips not make it run hot.  The 
usual reasons for hot running are:

 Over voltage!
 Excessive bus loads (capacitive or resistive)
Since the machine is a closed system for the most part the first is
most likely and the others are least likely.

I may add that over 60C is way too hot at the heatsink and the die 
due to thermal resistance will be hotter.

I'm trying to pull down one of my uV2ks and fire it up.


>Subject: Re: VAXstation/MicroVAX 2000 CPU/FPU overheating?
>   From: "Dave Dunfield" <dave06a at>
>   Date: Fri, 29 Feb 2008 08:18:31 -0500
>     To: "General Discussion: On-Topic and Off-Topic Posts"	<cctalk at>
>> I assume these CPU and FPU chips are MOS devices. Is it possile that 
>> excessive leakage across the gate oxide layer in some transsitors of that 
>> chip would cause it to run hot, but still work? I'm pretty sure I've seen 
>> chips that seem to work, but get hot and then stop working, althoguh 
>> cooling them with freezer spray keeps them running. And these were not 
>> chips  driving high pwoer laods -- they were things like the clock/timer 
>> microcontroller in a VCR.
>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?
>Perhaps I've been engaging in the persuit of an undomesticated ornithoid...
>Is it possible that the devices normally run this hot, and the failure is
>occuring for another reason (possibly a side effect of the heat, as cooling
>them does allow it to keep running).
>Allison said "they do run hot" - does anyone know how hot?
>I did some further tests last night - I dug out my thermocouple and made
>some actual heat measurements with the system assembled, but with the color
>frame buffer removed - there should be better airflow, and this appears to
>be the case, since the machine did not die after 10 minites of operation.
>Ambient temp was measureing about 25 degrees C at the start of the test.
>>From power on, the CPU and FPU rose rapidly (within 3-4 minites) to
>the 70C range, then more slowly rose to temperatures of 76C for the CPU
>and 82C for the FPU after 10 mins. At this temperature they seemed to be
>getting stable - having done nearly 1-1/2 mins without an increase. It's
>possible/likely that they would climb anothe few degrees in extended
>Once this temperature was reached, I held the system in RESET, and
>observed that the temps dropped back after a few minites to about 64C
>for the CPU and 68C for the FPU.
>To my mind, a processor running at 80C is damn hot - most of the embedded
>devices I work with list absolute maximum running temperature as 70C or
>75C - but perhaps the DEC devices are designed to run hotter - I note the
>Intel 486 datasheet lists absolute maximum (under bias) as 110C ...
>Anyone on the list with a VS 2000 or uVAX 2000 that can do some temperature
>dave06a (at)    Dave Dunfield
>dunfield (dot)  Firmware development services & tools:
>com             Collector of vintage computing equipment:

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