Powering up a 20-year old MicroVAX II

[Rick Murphy]

At 05:04 PM 2/21/2009, arcarlini at iee.org wrote:
>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
>ensued.
>
>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 :-)).

If the cables between your power supply and the backplane are ribbon 
cables with IDC connectors, they can overheat (often you'll find them 
showing discoloration.) If they're separate wires with white connector 
blocks, you have the updated harnesses.

I haven't seen this problem with BA23 boxes, but have seen several 
BA123 boxes with signs of overheating.
         -Rick