Making the repair on the core stack - part 2

BIT 7 WIRES SOLDERED ON THE JUMPER BLOCK PINS - EVENTUALLY

Just as I had done yesterday with the wires for bit 9 sense/inhibit windings, I soldered the wires to the appropriate pins (B12, B13 and D13) of the F4 jumper block structure. As I was working on the wires, the two sense lines broke off the core plane. This was a setback.

The metal that the wires attach to on the edge of the core plane is some kind of soft tin like material. This is probably the right material to bond the fine wires that suspend the cores inside the plane, but it is not designed for soldering. I think that IBM spot welded the wires to the metal during construction of the core stack. 

It was quite challenging to my soldering technique, but I did manage to get the metal to accept some solder in the end. The points where the wires were attached are right along the edge of the core plane and surrounded by many other small points. Very little separate, plus the triple wire cables run around that area. I had to use the stereo microscope and have a very stead hand to be able to heat the pin and wire without hitting the other points and wires that are less than a millimeter away.

I used the ohmmeter to verify the connectivity and low resistance matched the working sense lines, as well as checking that I didn't affect the nearby sets of wires where I had cut wires from the S-clip connectors. 

ANOTHER BAD CONNECTION FOUND

During that testing on the F4 and H4 blocks where I made my attachments, I found another signal that was bad. This one was for bit 11 in the upper 4K of memory. I was certain I had tested this and it worked properly a couple of days ago. Perhaps the work done near the S-clips and around F4 and H4 pushed another trace over the edge. So far, all the connection faults are on these two jumper blocks, which are the top two of the eighteen for the memory. 

I removed the wires from the S-clip area, routed them up to their pins on H4, dug out a relief channel in the plastic block, and then soldered them on. Another round of testing, this time covering every sense/inhibit wire in the machine, showed that no other connections are bad. 

INSTALLING CORE STACK BACK ON BACKPLANE

It was tricky to get the core stack remated with the backplane, because there were 10 pins sticking up from each of eighteen jumper block pads and all 180 had to fit through the tiny holes in the backplane. The slightest misalignment of a pin would cause it to jam against the backplane unless some wiggling got it to enter the hole. Cumulative misalignment in differing directions would render the wiggling ineffective.

This was quite a challenge as I tried to reinstall the stack. The IBM maintenance documentation for core memory replacement simply details the steps to remove it, ignoring any advice on how to get it to fit through the holes for installation. 

It took about a hour of very patient work before I finally (!) got the pins to all fit through the holes and could screw down the core stack. 

Core stack behind this with the pins sticking out of holes

The stack is held to the back of the backplane with four screws, which I installed. 

Attachment screw

VERIFIED ALL SENSE/INHIBIT CIRCUITS AGAIN BEFORE PROCEEDING

After the stack was securely mounted on the backplane, I once again checked the continuity and appropriate low resistance of all the sense/inhibit wires for the machine. Ten wires per bit, 18 bits in the machine, but all 180 connections are now working well. 

INSTALLED THE EIGHTEEN JUMPER BLOCKS ONTO THE BACKPLANE

This bonded the signals of the backplane circuitry and the core stack. It is now electrically joined and ready for the SLT cards and reinstallation into the IBM 1130 frame. 

+The frame where it will be installed