TESTING OF INTERNAL CONTROLLER REVEALS MAG PICKUP FAILS AGAIN
I hooked the scope up to the Index Marker (IM) signal line and saw zip. I then noticed that the behavior of the reader indicates that the original problem I had with the magnetic pickup is back. That is, the pickup is not delivering pulses at all. Those are important in order for the reader logic to recognize that a card is feeding through the photocells and to time the points to read the eighty columns.
I was working on finding the open circuit in the pickup when I found it working again, so I simply installed a new cable and put it back into the reader. It seemed to work properly for a while but just as randomly the connection has failed again.
I am going to attempt more significant surgery on the pickup - cutting into the sealed block and inspecting until I can clearly spot the broken wire. I am assuming that it is broken from where it exits the wound coil up to the point where the external cable is attached; in that case, if I can see the break I can repair it. If it has failed deep in the windings, I am out of luck.
The alternative is to get another pickup that can detect the teeth of the wheel and generate pulses to feed into the logic circuitry. That may involve machining a different holder since I would have to be extraordinarily lucky to find a substitute with an identical size and shape.
WORKING THROUGH MY MANY BAGS OF IC CHIPS TO DISCARD FAILED ONES
Over the years I have acquired plenty of integrated circuits, with some of them coming from auctions, surplus shops or other sources where I can't be certain that the chips are new and working well. The range of chip types is very wide, including many rare or obsolete versions that are not supported by most chip testers.
The 8bit-museum.de Retro Chip Tester Pro that I built covers a more comprehensive set of devices - far more than the other testers I have used. As a result, it has tests built in for the majority of the devices I attempt to test.
I spend time on every visit dumping out bags of chips, sorting them into lots of the same part number and then testing them. I have found a few bad chips. Just as importantly, I have satisfied myself that the bulk of these devices work correctly and can be used in future projects.
ARCHIVING MORE BOXES OF PUNCHED CARDS
I used the 600cpm reader to archive another one and a half boxes of COMMON programs. These have read fairly reliably, although the heavier work is studying, testing and documenting them afterwards. I also tried to read more of the DMS R2 M12 deck but these cards are very touchy to scan. The rate of misreads, either on the first pass or on the verification run, forces me to take them 20-30 at a time and feed them perhaps five or ten times before I get a good captured file.