DEC PDP-11/45 backplane +5 ECO

[Fritz Mueller]

> On Apr 24, 2021, at 7:02 PM, Josh Dersch <derschjo at gmail.com> 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 wirebarn.com 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!

  --FritzM.