Powering up a 20-year old MicroVAX II

arcarlini at iee.org arcarlini at iee.org
Sat Feb 21 16:04:43 CST 2009

cctalk-bounces at classiccmp.org wrote:
> IMHO the most important thing to do after checking for
> obvious problems
> -- loose parts, evidence of overheating/burning, etc, is to test the
> power supply (PSU) on a dummy load. A defective PSU could
> wipe out every
> chip in the machine!.

In addition, pay particular attention to the PSU wiring harness.

The early rev of harness on (iirc) the BA23 had a habit of
catching light. I think it was slightly underrated for the
maximum power load and so would deteriorate over time. It
would eventually reach the point where one of the N conductors
would fail, leaving N-1 carrying way too much load and smoke

Field service were (again, iirc) supposed to swap these out if
they came across them. But if your machine has truly not been used
for twenty years, it ended up in storage relatively eraly in its 
life and so may not have had a chance for some FS TLC.

A little bit of googling should find you the relevant details
(or you could wait for the next post which will no doubt be
from someone with much better memory than me :-)).

The only other thing I would add to Tony's post is that once
you think it isn't going to fry your boards (or burst into flames)
then you only need the CPU and one memory board in. Then you hook
up a terminal to the console (9600-8-N), set the switch properly
and check that you get some kind of life on the console.

At that point you can start to add the remaining boards (checking
that Qbus grant continuity is OK as you go) and build your system
back up again.

There are plenty of docs you can track down on Manx
You can google for the various Micronotes too, some of them are relevant
to the MicroVAX, others to the Qbus, and all of them are interesting
background reading.

arcarlini at iee.org

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