Friday, September 19, 2014

Booted diagnostic card from card reader, diagnosing failure of disk drive to load heads, wiring work on new keypunch interface


I polished up and cleaned the metal plates and plastic covers for the various stations where cards will sit. This was enough to get the reader to reliably load a card into pre-read and turn on the ready status. I stuck in a one-card diagnostic which I had laboriously punched out on the manual punch before I received my 029, readied the reader and hit the well known three key sequence on the 1131 - imm stop, reset, and prog load.

The machine booted in the card and ran the program. The program was sitting at its first wait condition where the operator confirms that the step worked properly, then allowed me to push start and continue through subsequent steps. This validates a considerable fraction of all the card reader circuitry both in the 1442 and in the 1131.

The cornering station, where the cards will stop before being accelerated forward into the stacker assembly, is still a problem. I had polished the plate and plastic, adjusted the height of the plastic lid, but there is still way too much drag on the card. I will repeat my polishing and cleaning until the card slides with similar resistance to that experienced in the pre-read station.

I implemented the extra switch to override the hopper empty switch, based on an excellent modification developed at The National Museum of Computing in the UK when they were restoring their 1130 system. I hid the switch behind a blank button, but when I pull the button cover out, I can easily flip the switch. This allows me to inject streams of cards using the NPRO function, a good way to validate the quality of the card movement inside the reader.

Panel, with my added switch hidden behind white blank button

Button revealed, allowing override of hopper empty condition for NPRO

The internal disk drive will spin the cartridge up but never loads the heads down onto the disk surface. If I manually move the solenoid to load heads, it will latch in and the heads seem to be flying well, but I had to figure out what conditions were not being satisfied to do the loading. I began with the oscilloscope where I quickly saw that the 90 second timer was not going off.

Logic card cage in disk drive, where I traced signals with scope
Testing the time delay relay and learning it never energizes
The timer is a relay that is powered at the same time as the motor is started. The relay continues a transistor and an RC circuit to cause it to wait 90 seconds before it energizes. However, it is not energizing at all. I removed the relay and did further testing to see what was wrong and whether I can correct it.

Time delay relay that is not working
After looking it over, particularly considering that all this relay does is break a signal connection to ground, to allow it to be pulled up to logical 1, I decided to find a replacement time delay relay. It need not be a direct substitute as long as it works with 48VDC power, can be set to 90 seconds and will open a circuit once the time has expired. I found a unit online and have it arriving Monday.

taking relay apart
timer circuit

K2 is the time delay relay, will replace with different type

I began assembling the cable with the appropriate pins and connectors to install it onto my keypunch. I don't yet have all the connectors I need but they are coming later today, after which I can resume this task.

The reader cable, which senses the absence or presence of holes in the 12 rows of the current card column for the card going through the dup station, was connected solely to the relay panel and I had enough push-in pins to finish the wiring. After soldering the connectors to the appropriate wires from the DB-25 cable, I installed it onto the logic gate.

connectors on to the wire on the cable
Reader cable installed

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