Thursday, November 6, 2014

More keypunch debugging, further assembly of the SAC interface box, and an interesting test tool

I had to visit the Consulate of China to apply for a visa for a stopover I will make in December in Shanghai. Two hours round trip to get there plus almost two hours waiting to file my paperwork - all valuable time taken from the 1130 restoration.

Maglev train in Shanghai
My visit will only be a couple of days but one of the things I am looking forward to experiencing is the magnetic levitation train that runs from the airport to a transportation hub. It will reach a peak speed of 430 kph (about 270 mph) - it will feel like a trip into the future for an old science fiction story fan.


I did more testing and validation - still having problems getting the timing right for the read of a card going through the dup station - but the rest seems to be working perfectly. I spent time with the keypunch documentation and derived some relative timings but they don't work in practice.

Interface being debugged
The activation of any hole magnet or the space magnet causes a set of contacts to close which energizes the escapement relay in the keypunch. Supposedly, it takes 12 milliseconds for the card to move to its new target column, after which the punch clutch is triggered starting a punch cycle.

The punch cycle is 50 ms overall, with the pins at their best point to sense at 17-18 ms into the cycle. Based on this, I assumed that the cumulative duration  is 12 + 17, thus if I read the pins at 30 ms after I trigger the punching for the column, it would be the right time. However, the pins are not extended enough to make any contacts, registering every column as containing a space.

My earlier experiments found non-space results at 40ms and 60ms after I trigger a punch, not the 30ms I used which failed. I will work on this more deliberately tomorrow, identifying the range of times when the pins show good results.


I finished the corrections on the first board, installing the replacement resistors for those positions where I had mis-installed the pairs backwards. In addition, I have eleven sets of driver and receiver circuits assembled on the third board, just one more to go. One more board will be needed to hold five more driver circuits. A bit more soldering of components, then wiring of power and TTL signals to the boards, and then I can test these out.

Boards one, two and three from top to bottom


I found an interesting looking tool on eBay, a suitcase unit used by IBM labeled the IPAT 5800 unit. I saw some bus and tag terminators along with ribbon cable, which made it appear to be useful for some kind of IO channel testing. I was able to get it for a low enough price to be worth the gamble.

Inside the briefcase

Control panel - selecting cable, lines and a few test types
Chart to interpret distances of malfunctions
The unit sends pulses down various lines in the cables, displaying on an oscilloscope and allowing the identification of the type and location of any problems - break in a wire at xx feet along the cable, or short or open instead of proper termination - designed to work with 360 style bus and tag cables but also the twisted pair type cables used with the 1130 and with coax cable as used with 3270 terminals.

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