Need picture of power supply mounted in 11/40 cabinet

Noel Chiappa jnc at
Wed Dec 8 12:16:14 CST 2021

    > From: Marc Howard  

    > I've got an 11/40 I'm going to start working on. Problem is that there
    > are two power supplies (H742 and H7420) that came with it but neither
    > was mounted in the rack.

-11/40's in general only have one of those large H742x suppplies in a rack.
The documentation and prints all show only a single one - in fact, the 11/40
power harness (which is specific to the KD11-A backplane, at the CPU end) can
only attach to one. The KB11 machines (-11/45 and /70) use two, but their
harness has provision for two.

I don't know of a DEC document that lists the difference between the H742 and
H7420, but my CHWiki page for them:

gives what I think is a pretty good list; any errors or missing details would
be appreciated.

    > Also how is the power cabling routed (I think I'm missing this part)?

That's going to be a hassle, replacing the main harness! Especially since
production of the 8-pin MATE-N-LOK connector shells used to interface to the
H744/etc 'bricks' - part numbers here:

are out of production, although some vendors have residual stocks. Hoard them
while they last!

The "PDP-11/40, -11/35 (21 inch chassis) system manual" (EK-11040-TM-002):

has pretty good coverage of the harness; the back end of Chapter 6 covers it
in detail. That's a lot easier to understand than the FMPS:

so read that before you tackle the prints.

Note that there are two different kinds of harness, depending on whether the
machine has MM11-L (-15V) or MM11-U (+20V) core memory. Unless you're
planning on using one of those, you can probably ignore that, though.

Any questions, ask here right off; we have a lot of expertise! :-) ('My'
first -11 - as in, one I was in charge of - was a -11/40. Fond mempries!)


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