Wednesday, December 17, 2014

Fighting the last problems with the printer

As I had mentioned, I spent time meeting friends from the 1401 Restoration Team at the Computer History Museum and then had my haircut in the afternoon, but did get into the garage for a few guilty stolen moments.


Wrestled the C2 contacts into position to give the intended timing, breaking the circuit as the print cycle hits 20 degrees of rotation and making it again as we pass 120 degrees on the way to completion at 180. This timing is related to the realities of the selection mechanism, which has released the various latches before 120 degrees, at which point the type ball is rotated, tilted, locked in place and just about to strike the ribbon/paper.

If the print solenoids are activated at this point, they will lock in the next character but not interfere with the remainder of the current print that is in process. However, the cycle clutch latch won't stop the rotation, allowing the machine to continue smoothly into another print cycle based on those solenoids which were activated late in the prior cycle. This maximizes the print speed of the machine and reduces stop/start shock.

The device adapter logic in the 1130 is responsible for monitoring the circuit that goes through C2, holding off until the 120 degree point before commanding the next print operation. If electronic hardware were not so expensive at the time these systems were designed and built, a digital buffer inside the 1053 could have accepted the command for the next character and held it until it was time to activate the solenoids, simplifying the requirements for device adapter logic in systems like the 360 and 1130 that drive these printers. Instead. the 1131 directly drives each solenoid and must monitor mechanical state of peripherals in order to time activities correctly.

I have a selectric based mechanism in a Dura word processor that I will restore to act as a 2741 terminal on my 1130 system, but it does have a motor pulley of the same type as I need. I will 'borrow' this one and back-fill with a replacement part I can put back on the Dura. Installed now on the 1053 and working well. I still have some motor vibration, not sure why, but it is not the pulley slots anyway. Quieter and more gentle, so progress for sure.

The carrier return issue with zooming past the left margin stop is still here, at least under power. I need to do more research to figure this out and stop it, now that the printer is so close to operational again. By the end of the evening, I still didn't know why it was hit or miss. Time to step through the adjustments for the high speed carrier return starting at step 1.


I decided to pull the read/write heads from the Diablo disk drive in the CHI cabinet, in order to find someone who can restore them to working condition. There had been a number of businesses that did this with disk heads, back before the heads were permanently integrated into the drives and not worth rebuilding. If I can find any that still exist, I can get the Diablo drive back into operation.


Still looking for a way to get those four leads soldered onto the fpga board, particularly the three that are side by side and thus can't be individually attached (the soldering iron loosens adjacent wires). Ron Crane had some good ideas for how I can proceed, will try them out.

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