PDP-11/44 want list

From: Lancashire, Pete <PLancashire_at_columbia.com>
Date: Wed Nov 5 15:26:19 2003

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

-pete

-----Original Message-----
From: Tony Duell [mailto:ard_at_p850ug1.demon.co.uk]
Sent: Wednesday, November 05, 2003 1:06 PM
To: cctalk_at_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
Received on Wed Nov 05 2003 - 15:26:19 GMT