After removing all the boards and leaving just the
disk and tape drive for
load I impetuously decided to try powering it up. I knew the PSU (model
Personally, I'd not have used a disk drive (presumably a winchester-type
hard disk) as a dummy load. If might well contain interesting software.
But anywy, I would be very suprised if anything on the output side of the
PSU has been damaged,
H7864) was set for 110V and made the switch to 240V (I
am in the UK). When I
connected the power cord, after a few moments there was a loud pop, followed
by another before I could pull out the power cord, smoke rose from the PSU.
This sounded just like when I had once accidentally made a 110/240 mix-up.
The question is, could it be that I had not made the switch to 240
correctly, or could this just be down to the age of the PSU?
I don't know the MicroVAX PSU that well (another list member wants me to
dig mine out, take it apart and work out how to repair said PSU...) but
my experience of DEC hardware is that if there's an obvious external
voltage selector switch, that's all that needs to be changed. If there
isn't (at least on older machines) there may be one or more sets of
terminals inside to rewire. But I've never seen both.
Of course on large systems there may be voltage selectors for each
sub-unit (CPU, expansion box, drives, etc), but the Microvax II is in one
cainet with one PSU.
My guess is that it was just bad luck. Something in the PSU decided to fail.
The next thign to do is to open up that PSU and see what has failed.
Often it'll e obvious now. Look for burnt reisstors, exploded capacitors,
blown PCB tracks, etc.
-tony