Each jumper block connects three sets of sense/inhibit wires, three wires each. I used the ohmmeter since the wiring was isolated due to the jumper removal. In addition to the continuity break of one sense winding for bit 7 of the low 4K of memory, I found another break! Bit 9 for the high 4K of memory also had a high resistance in one wire. One was in F4 and another was in jumper slot H4.
I put one side of the ohmmeter on the pin from the jumper block area (F4) and verified that the loss of connection was from that pin up to the S clips that anchored the three wires running to the sense/inhibit windings for the low 4K of bit 7. The sense/inhibit wires were intact as were the three wires running to the S-clips.
The same was true for the broken connection on jumper block area H4 - no connection from jumper block pin to the S-clip but good connectivity over the three wires and inside the core plane for bit 9. The same failure mode.
WHERE TWO ARE BAD, CHANCES ARE MORE WILL BE BAD
If I found a bad connection in each of the only two jumper blocks I had removed, it would be difficult to believe that none in the other eight jumper blocks were bad. I now was committed to pulling the jumper blocks off, rather than proceeding with the repair plan I discussed yesterday using the T-3 connector.
I created a tool to help me pull off the jumper blocks that were wedged side by side leaving almost no room to slip anything between them. I got them all off so that I could test all the other sense/inhibit wire sets. At the same time, I pulled the jumper blocks that carried the read/write gate and driver wires up to the diode board and the X/Y wires.
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| All jumper blocks removed |
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| Bottom rows of each slot have core plane pins sticking out |
REMOVING THE CORE STACK FROM THE COMPARTMENT AND BACKPLANE
Since I had the jumper blocks removed, the remaining work to remove the core stack was relatively minor. I decided to pull it off so that I could either repair the traces that were broken or make a more straightforward connection to replace it.
The core stack is attached to the backplane with four screws, then it would be pulled away from the backplane which pulls all the pins from the core stack out of the holes in the backplane. The screws had been glued into place, so that I couldn't get most of them to turn. I decided that I could remove the entire backplane with the core stack still attached, then on the bench I could separate the two more readily.
The backplane is held onto the frame by some bristol head socket screws and plastic holders. I removed these, disconnected the power connectors to the board, and lifted the entire assembly out of the frame. Putting it on my workbench, I could get better access to remove the screws holding the core stack onto the backplane.
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| Corestack still mounted to backplane |
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| Wire wrap/pin side of backplane |
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| Card slot side of backplane |
With the core stack removed, I saw that I wouldn't have access to the traces that ran from the S-clips to the pin blocks unless I unbolted the entire stack and pulled the layers apart. The risk of damaging connections was far, far too high so I didn't do that.
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| Bottom board of core stack with jumper pins |
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| Top side of core stack with S-clips at top left and top right |
REPAIR PLAN IS SIMPLE
The pin blocks for the jumper pins were right there and it was obvious that I could run a wire up to the S-clip area and solder it on. That is the repair I will do, running new wound triple wires from the pin blocks to the S-clip area instead of relying on the traces on the core stack bottom board which were defective for two of the lines.
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