DEC PDP-11/45 backplane +5 ECO

Josh Dersch derschjo at
Sun May 2 15:25:34 CDT 2021

On Sun, Apr 25, 2021 at 11:26 PM Fritz Mueller <fritzm at> wrote:

> > On Apr 24, 2021, at 7:02 PM, Josh Dersch <derschjo at> wrote:
> > If you have notes on re-creating the harness, let me know.
> Hi Josh,
> A few pointers -- I think I left some of these in a comment on one of your
> fb posts, but will repeat here in case others may find it useful:
> * The wire list in the commonly available Jun74 11/45 engineering drawing
> set is actually for the power harness, and not for the backplane.  It
> includes wire run lengths in inches, which is quite handy.  I believe it is
> for the newer harness, but there is much overlap.
> * The old and new harnesses are also schematically illustrated on four
> pages of the drawing set marked "power systems configuration".  These
> drawings are complete and quite good.
> * Drawings for the power distribution board for the older wiring style
> (vertical at the back of the cabinet) are hidden in the Jun74 11/*40*
> engineering drawings (upper right of sheet BA11-F0).
> * What I did was use the wire list lengths as a guide, cutting each run to
> length plus a little extra.  I then started with the H742s on the bench, at
> the regulator and power monitor mate-n-loks.  Then put the H742s in the
> rack with the CPU cabinet, and worked my up and over the and then down
> along the along the backplane toward the console, bundling and trimming to
> length as I went.
> * A good ratchet lock crimp tool makes a big difference here.  You want
> one with a die that can handle 14 AWG, and on which will crimp both the
> electrical and strain-relief parts of the pins in one go.
> * Sticking with the original wire color code also makes it a lot easier
> not to get lost and later to double check and troubleshoot your work.  I
> used MTW ("Machine Tool Wire"), which is available from at
> 14 and 18 AWG in most of the necessary colors and in 25 and 100 foot
> lengths (I think the 18 AWG purple I had to find separately on eBay, but I
> have lots of leftover of that and will gladly send you some.)
> * I skipped wiring for most of the regulators in the bottom H742 (I have
> regulator F there, but none of H, J, K, or L are populated) because I don't
> have any core or fastbus memory in my system.  I figure I can add this
> later if I ever do find myself with either of these.
> Good luck!

Thanks!  I may get started on that fairly soon, we'll see how ambitious I'm

Sorry for the delay, but finally, here's a pile of pictures of the +5V ECO
on the backplane.  Let me know if you need more detail on something:!Aqb36sqnCIfMpMAqf_6YvmsEEU-T0A?e=Y6WBfV

- Josh

>   --FritzM.

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