I have had a PDP-11/24 for some years, working just fine (last time I had
it on was about last May).
Yesterday it decided not to work. Looks like the H7140 supply. The +300V
on the voltage doubler is there, but the +13V in the Bias/Interface board
reads about +7V. I suspect this is central to the problem. (The +12V Bias
is also reading about +7V).
When I turn the console power switch, I can hear the contactor in the power
control unit in the rack, so I don't think it is the switch itself.
When I flip the breaker on, I can hear a "chirp" as though an oscillator
starts up. If I flip the breaker off, then about 10s later I can hear the
chirp of an oscillator shutting down.
Any words of advice? Does anyone have a technical description of the
H7140? I have schematics (and can read them at the component level), but
power supplies are hardly my strong point -- it would be useful to have
some description of just how this animal goes thru a power up
sequence. Plus, blind diagnosis will be slow -- there aren't any test
points, and one needs to make sure the +300V from the doubler has been
bled off before yanking cards to solder test tails at strategic points. It
would be helpful if someone could give me some guidance so I knew more
about how this thing works.
Jay Jaeger
---
Jay R. Jaeger The Computer Collection
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Received on Sun Nov 11 2001 - 16:11:48 GMT