PDP-11/44 want list - test-drb@ccmp.vtda.org

5 Nov 2003

and didn't the thing have to have a load to test it ?

-pete

-----Original Message-----
From: Tony Duell [mailto:ard@p850ug1.demon.co.uk] 
Sent: Wednesday, November 05, 2003 1:06 PM
To: cctalk(a)classiccmp.org
Subject: Re: PDP-11/44 want list

...

 John
 On Tue Oct 8 20:11:58 2002, you posted about your 11/44.
 I was searching for help with the H7140 power supply when
 I came across your post.  I recently tried to power up
 a system I got a couple years ago, and have a flashing 'DC On' 
This generally means one or more of the power rails is out-of-spec...

...
  indicator.  I don't know how serious this is, or
if I might be able to 
...
  repair/adjust it with some guidance.  Suggestions? I
have no 
 documentation on the power supply. 
You _need_ the schematic. The H7140 is one of the most complicated PSUs 
you'll ever come across, and it's also dangerous inside. There's 
rectified mains (400V DC at essentially unlimited current -- the 
smoothing caps are the size of coke cans!) on screw terminals on the top
of 
some of the PCBs. This _will_ kill you, if you touch it. Not 'might',
will.

Basiclaly, there are 3 switch-mode PSUs in that box. The first is a
small 
one, used to power the PSU control circuitry. The second provides the
+5V 
and +/-15V logic supply rails. The last provides a +36V rail that can be

battery-backed. That one is then regulated down to +/-12V and +/-5V for 
the memory boards. It also supplies the H-bridge driver that provides
the 
35V 70Hz supply for the fans.

The schematic for this supply is a dozen or so pages. I wouldn't want to

work on one without it in front of me, even though I've repaired them 
before...

-tony