Sunday, September 28, 2014

Finishing new keypunch interface unit, progress testing the 1132 and a bit of work on card reader and disk drive


I spent many hours carefully wiring together the interface, using the connectors, checking wiring and soldering, double checking which wire I was holding before putting it on a connector. At this point, the unit is closed up but one task remains before I begin code development and testing. I have to install a power brick inside and a suitable molex power connector, then wire up the corresponding connection inside the keypunch to bring power to everything.

Wiring complete other than power brick
A lot of connections, finally complete
Wires soldered to header pins, inserted in the Arduino
Molex connectors hooked to relay board, barely visible mid-upper right

Unit closed up until I add the power brick and start testing.
I am will be unable to work on the machine from Tuesday through the following Friday due to intensive business commitments, thus will wait to do the exploratory testing and hardware checkout until I am back in the workshop.


My next step to get the cards moving from the cornering station to the stackers is to increase the pressure on the rollers pulling the card into the stacker area. I began to adjust the indicated screws but I need to spend more time to be sure I get this pulling more firmly. I don't want to introduce skew into the card movement, which is possible if the pressure on the two rollers is not the same.


I put in some fresh paper and reloaded the test program. I have an instruction which is supposed to decrement a counter each time I find and print one of my target letters, but the value in that counter, index register two, is not going down. After a look at the program, I realized I was using hollerith code (card reader and keyboard), not 1132 printer codes.

Instead of stopping when I get four matches, I am going to take 48 read emitter interrupts, which is one complete cycle of the print wheels. That should ensure I issue the scan codes to print in all eight of the last columns.

Running with the full 48 character interrupts gave me a satisfying sound of printing, but the page was blank. I probably have a ribbon that is so dried out there is essentially no ink to transfer. I pulled out a spare ribbon, which is about 25 years past its 'use by' date but might just have a bit of ink left. I had to read the manuals to learn how to change the ribbon, but I did get it changed.

It was definitely full of ink - got on the printer cover where I rested the ribbon spool as well as on my fingers! Running the print program again produced very slightly darker letters but only in a few spots. It appears the print hammers are likely partly glued with old lubricants and can't snap crisply into the print wheel.

Ink stains on printer top from the replacement ribbon resting there temporarily
Only some of the hammers can leave an impression, others don't strike with enough force. I also see one case where the letter D printed in the column where I was requesting to print a C. Since that is the next sequential character after the one I requested, it is consistent with a gummed up mechanism latching up too late to match the C.

The next step for this unit is to clean the old lubrication from the hammer and print related moving parts, putting on new oil and making sure it is all moving freely. Once that is done, I can try the print test again and see where I am in the restoration of this device.


I toyed around with the broken delay board from yesterday, finding a way to get it triggering but not correctly. With the original capacitor, it worked on a 10 second delay which is too short for my purposes, thus my second set of tests were with a much larger capacitor to produce a longer time interval.

The first tests, with the 10 second time interval, were supposed to show a turn on delay, meaning the circuit should start with the relay off, wait ten seconds, flip the relay on, and stay in that monostable state while power remains on. Instead, it began latched, then each ten seconds it turned the relay off or on, alternating forever in a bistable mode. It should not be oscillating.

The second tests, with the longer interval, showed even stranger behavior. It would start out active, blip the relay off and on for less than a second, wait the long interval, then repeat the blip. Each interval had a momentary blip and a long wait. Again, not useful for my purposes.

My working assumption is that the LM555 chip (timer) that is the heart of the circuit is malfunctioning, since all the components seem to have proper values and be wired correctly. I desoldered the chip from the board, using my hot air rework gun, and will pick up a surface mount 555 chip to replace it. I am feeling hopeful that with a bit of work I can get this board doing what I want, replacing the original time delay relay in the disk drive startup circuitry.

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