DEC backplane repair

[Charles H. Dickman]

What is the best way to fix a wire wrapped backplane?

I have a pdp-11/40 with a short to ground in one of the backplane runs. 
I probed the backplane with a wooden stick and with some wire tyes and 
the short went away. I have a pretty good idea which segment of wire is 
the problem. I have probed the area again and I can't get it to come 
back. So, what should I do?

1. Be happy it is working. Note the problem in my log book. Wait for it 
to happen again.

2. Replace that run in the backplane.

I figure I will have to replace most of the run because this segment is 
on the lowest wrap level and in the middle of the run, so I have to 
replace this one and the ones on either side.

I have done some wire wrapping, but this thing is very intimidating. 
Replacing the wire is easy, but I am afraid that taking out the old ones 
will create another problem. These backplanes have the wires pretty 
taught and they are pulled over square edged pins. How fragile is the 
backplane wiring?

If you have a PDP-11/40 then the KM11 is your friend. I have been 
troubleshooting this problem for a while, but after I handbuild a KM11 
(from Tony Duell's notes), the problem was obvious.