H7140 PDP 11/24 Power Supply Advice

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 cube1(a)home.com visit http://members.home.net/thecomputercollection