VAXstation/MicroVAX 2000 CPU/FPU overheating?

Allison ajp166 at
Fri Feb 29 09:19:51 CST 2008


I pulled out NETBOT:: a 12mb uV2000 with a RD53 and booted it with the 
case off to get the temp and the hotter of the two chips stabilized 
at 58C +- a tiny bit while running VMS 5.4-3.

Like I said they do run hot.


>Subject: Re: VAXstation/MicroVAX 2000 CPU/FPU overheating?
>   From: Allison <ajp166 at>
>   Date: Fri, 29 Feb 2008 09:50:52 -0500
>     To: cctech at
>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!
> Overclock
> Undercool
> 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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