Monday, August 31, 2015

Still battling persnickety selectric typewriter mechanim. Wired up the board to emulate the Prog Load button for virtual 2501 reader


My adjustment for the carrier return latching issue has corrected the problem. I now sails across to the left margin whenever activated. Making progress. The unlatching when it reaches the left side is better but still will occasionally fail to fully unlatch. In those cases the movement seems mushy also.

I remain very happy with the character selection and shift operation of the console printer. I get every letter, typed cleanly, in both hemispheres. The remaining problems are generally independent of each other, allowing me to attack and fix each one in whatever order suits me.

I have adjustments for the carrier return unlatch, after I do a basic test with a spring scale to verify that the leftward pressure is appropriate. It should be around 2 pounds of pull to the left. I can adjust the governor that establishes the amount of pull.

I still have a few issues which I am working my way through, in addition to the carrier return failure to reliably unlatch at the left margin. Sometimes the index operation sticks on and feeds down many lines before it releases. Tab is still not adjusted to activate under program control. Lastly, I still see some poor spacing especially all the way at the left margin.

The poor spacing is likely the dastardly solidified lubricants which are so hard to completely flush from the unit without a total disassembly and bath in solvents. With continued use, this will improve, but initially I can just set the left margin over more to the right, to avoid the region where this occurs.

It may also be that my space escapement lever isn't moving far enough, so that at the end the tooth is just barely touching the rack. I will try to make some adjustments later to see whether this helps, but not today.

The runaway index is a failure of the interposer restorer to latch it back up - a matter of inspection and adjustment. It may also involve a missing spring out of the untold hundreds of tiny springs that are sprinkled across this mechanism.

Relatching for the indexing interposer was being blocked by a loose, excess spring down in the mechanism. After I moved it out of the way, but alas did not extract it completely, the index seemed to fire once and reset quite reliably.

The tab issue remains open to investigation. Definitely something wrong in the whole interposer/trigger mechanism, but not sure what it is right now. Unfortunately, none of the service manuals or the diagrams in the parts list are a complete view of the mechanism and how it should be operating. I spent some time in the late afternoon studying everything I could on this section of a selectric.

When the other pull links are operated, they pull down on the interposer enough for the latch at the front to slip off, the spring then pulls the interposer back and it operates a cycle. No amount of tugging on the tab pull link will cause it to move down enough to slip the latch free, so it never moves backwards. Still no resolution.

I triggered both space and backspace operations, but the carrier was just dancing left and right a slight bit for both of them. Upon inspection I found that the tiny spring that holds the backspace operational lever towards the front had popped off. With both mechanisms tripping at the same time, the carrier didn't know which way to move. If I hold the backspace lever where it should go, a space operation works fine. I have the spring but attaching it is a PITA (pain in . . .), so perhaps later tonight.

The more I pull on the tab interposer, the more it seems that it is hung up on something, as it won't slide backwards as it should with a slight release, instead requiring a substantial push from the front panel button mechanism. Once it slides back, the tab function works just fine.

Some possibilities for the problem with the tab interposer:

  • loose spring inside somewhere jamming the movement
  • burr on interposer stopping it from sliding free
  • maladjustment of interposer (from among several adjustments)
  • misplacement of tab interlock swingarm

Once I can figure out and fix the tab issue, replace the spring on the backspace latch, and get the return torque adjusted better, and repair the ribbon color nylon cable, I expect to have a pretty decent console printer.


I spent some free time in the morning putting in all the wires on the emulation engine board so that I am only waiting for the ICs, resistors and capacitors in order to finish it up. I used a prototyping board which means I have to put discrete wires for each connection between pin pairs Over lunch I tested to be sure there are no shorts among adjacent lines and that every connection was proper and sound.

I am feeling a bit nervous about the clock speed of the emulation engine - designed to be 0.1 seconds - as the various switched circuits attached to 1130 buttons might need a bit more time. More importantly, I want to be sure that the PC program will see the machine complete its reset, then store all eighty words of the boot card image into core before the emulation engine presses the Prog Start button.

I decided to slow down the clock to 0.2 or 0.25 seconds. The entire emulated Prog Load sequence will still only take 2 or 2.5 seconds, which is fast enough to see immediate when the user pushes on the Prog Load button on the PC side program. I just needed to parallel the timing capacitor with another, to increase the total capacitance, thus increasing the RC constant of the circuit and slowing the timer pops. I will get a suitable capacitor later and test now at 0.1 seconds.

When the components arrived this afternoon, I wired in the resistors and capacitors, then did a final test for shorts and incorrect connections. I put together a quick testbench, hung the scope on the lines and listened to the relays as I triggered a cycle.

Initially it did not work satisfactorily, with the flaw being in its initialization and reset circuit. When it was running it counted up and fired the relays exactly as desired, but without resetting to the initial state after a cycle, it wasn't usable. I put it aside to mull over tonight and make adjustments to the logic tomorrow.

While running the 1130 to test and adjust the 1053 console printer, I was using the SAC Interface Box to reload the diagnostic program whenever it seemed to be wedged up. At one point, when I tried to power it back up for another round of diagnostic test loading, the box didn't fire up the fans or power supply. I have good power to the outlet and the cord looks fine, so I had a new issue to have to debug.

The connector for the AC input to the power supply itself, inside my box, seemed properly seated but a bit of wiggling brought the box back to life. With this resolved, I can go back to my testing tomorrow.

In the meantime, I expanded my UCW (unit control word), which keeps status for each of the twenty possible peripherals that can be hooked to the box, to include interrupt levels 0 and 1. The logic for setting, resetting and reporting the two new levels was added as well, so that once I have this enhancement wired into the 1131, I can start supporting virtual (PC based) and real (hardware hooked to the box) devices such as the 1442 and 1132 that require these interrupt levels. 

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