Return to main page

State of the 1401 facility

On Sep 19, 2019, Carl Claunch wrote:

CT SYSTEM The 1401 processor is working properly All four tape drives are working properly The 1403 is working properly. The 1402 punch side is now working properly. It would not NPRO, raising a punch stop immediately without spinning the motor. We guessed that it believed there was a jam that couldn't be properly ejected with a feed, although there is no indicator light to show this situation. We manually cranked the punch, ejecting two cards which we believed were too close to each other. The punch was tested both with NPRO and by punching output. The 1402 reader side continues to have intermittent problems but is in service. The problem manifests itself by a failure to take feed cycles - the load button is pressed, the motor spins but no cards are fed. This also occurs with a read op code in the processor and Start pressed on the reader. This problem occurs sporadically, lasts for a bit of time and then maddeningly goes away as we attempt to trace the issue to its root cause. By the end of yesterday, it appeared that the problem was a fault in the Interlock Stop latch which should be reset by the Load key or Start key but remains on. The fault disappeared before Ken and I could determine why the latch is erroneously on. Often a power cycle of the 1401 system will make the problem go away. DE SYSTEM The 1401 processor is working properly. The first and third tape drive are working properly. The middle tape drive requires adjustment of skew delays between tracks to properly read and write tapes and is currently out of service. Michael has been adjusting all the tape preamp and amp levels to the target of approximately 8V, up from seriously low levels on all three drives. Once we restored the signal levels, we encountered skew errors. These mean that the time from when the first 1 bit arrives from some track and the arrival of the last 1 bit from any other channel has exceeded some maximum acceptable delay. This requires us to adjust all tracks to cause their bits to arrive as close to simultaneously as we can. Adjustment is done by selecting one of a number of taps on a delay card - choosing among various predefined delays. All seven tracks have a delay card. We would watch the bit arrivals from the tape head for groups of tracks. to identify which were the furthest apart and begin changing those targeted tracks to bring the bit arrivals closer together. Marc discovered some "Skew Test Master" tapes in the workroom which should give us known good patterns for this work. We would have tracks that were written as close to simultaneously as possible, with all tracks having a 1 bit recorded. The 1403 printer is working properly. The 1402 reader side is working properly. The 1402 punch side is still being adjusted and is currently out of service. Frank, Dale, Alan and others are going through the 1402 maintenance manual step by step, adjusting the timings of the punch. The initial punch checks we were receiving were a result of mistiming in the mechanism that allowed cards to slip and skew. The punch moves cards two ways - continuously and with stop-start motion - which is what makes it mechanically complicated. The normal smooth motion takes place as cards are fed into position to punch the first (row 12) holes, and again when the finished card is moved though the read station and then into the stackers. Stop-start motion occurs to freeze the card while a row of holes is punched, the step the card forward to the position for the next row. The stop-start mechanism is built around a Geneva drive. The pinch rollers that cause smooth card motion are moved out of contact by cams to cause smooth motion to cease, then dropped back in place to restart smooth motion. This must be well synchronized since we want cards to roll up to the point where we begin punching holes for row 12, the stop-start mechanism to hold the card still and the cams to pull the pinch rollers out of the way stopping the smooth motion. If the smooth motion continues when the stop-start is holding the card still, we fold up the card into a jam. If the smooth motion stops at the wrong time, the card may be mispositioned for punching row 12, causing a miscompare when the card is read after the punching is done. The adjustment consists of lots of hand cranking of the mechanism, then adjustment of various screw settings, clamps and belt positions. The team is partway through the adjustment sequence. Once complete and after verifying punch operation, we can return this unit to service. CARD SORTER The sorter is operating correctly. KEYPUNCHES The two keypunches further from the entry door are working correctly. The keypunch near the door is out of service while the keyboard is repaired. This keypunch would lock up from time to time, with the problem becoming more frequent. We opened the keyboard to determine the root cause and found a worn part for the Space bar mechanism. The Space bar pushes down, rotating a lever to pull a long bar forwards towards the keypunch operator. This bar will trip a vertical bar in the rear of the keyboard which falls down. That swivels a number of horizontal bars in the permutation unit attached to microswitches. For some of the keys is also activates an individual microswitch under the vertical bar. The wiring of the microswitches in the permutation unit will convert a single pressed key into activation of some number of solenoids in the punch unit. The 'A' key will be converted to a 12 and a 1 punch, for example. Dual keys (e.g. U key is also the number 1. When in Alpha mode, this fires the 0 and 4 solenoids but in Numeric mode it fires the 1 solenoid instead. The long bar moving forward pushes apart small ball bearings in a horizontal chamber. These are packed together tightly enough that once a single key's bar as entered, there is no room left to let any other keys move. This ensures that one and only one key is pressed at a time. The forward movement of the long horizontal bar and the resulting downward movement of the vertical bar locks the key in place. Once the keypunch has responded to that keystroke by punching holes in a card, a solenoid under the keyboard is activated and it moves the restoring bail, a bar that pushes all the vertical bars up, all the long horizontal bars forward and the keycap back into its full up position. The interaction of the long horizontal bar and the vertical bar depends on a notch in the horizontal bar. This holds the key down until the restoring bail is activated. On the bar for the Space key, the notch is worn into a sloped ramp not a sharp edge. The result is that pushing Space will trip the vertical bar but latching the horizontal bar in place is temporary. Because of the slop, it easily slips off and unlatches. The restoring bail will fail to push the vertical bar back up if the horizontal bar isn't latched, thus the keyboard remains stuck. We have a spare 026 in the workroom whose keyboard we removed to supply replacement parts. The long horizontal bars engage with the vertical keystems under the keycap. The keystem is inserted into the top, fits around a coil spring and then emerges through the bottom plate. Nylon fishing wire is laced through all the keystem bottoms to keep them held in the keyboard. We had to remove the fishing wire, pull all the keys out, extracting the coil springs then opened up the upper and lower plates to get to the long horizontal bars. It was easy at this point to replace the worn space bar with the good one from the donor keyboard. At this point Alexei has put the plates together but has to tediously inserted each keystem, holding the spring in place with tweezers, then thread the nylon line through its bottom. He has done part of a row but will continue on the weekend trying to finish rebuilding the keyboard. You might ask why we didn't just swap the entire spare keyboard for the worn one? The wires to all the microswitches on the keyboard are soldered in place. This bundle runs down and is laced together with many other wires from the rest of the keypunch, ultimately being soldered to the strips inside the base where the tube logic resides. We judged the unwiring and rewiring process to be more difficult and time consuming than all the work detailed above. MANUAL KEYPUNCH (001) The manual keypunch at the railing in the computer room is working correctly. 029 KEYPUNCH IN LIEBERT ROOM The 029 is working properly NEW 029 KEYPUNCH IN WORKROOM This 029 has multiple errors and needs restoration. It is likely that the problems stem from oxide on the CB (cam actuated switch) and relay contacts, but we need to diagnose the conditions to be sure. This is a low priority task that will only be worked on when everything else is running well or a team member is particularly bored. 552 INTERPRETER IN WORKROOM The interpreter is in the midst of restoration, not yet ready for service This interpreter will take in punched cards, read the characters in the columns and print 60 of them on either of two lines across the top of the card. We intend this device to be used to print cards that were punched on the 001 keypunch by visitors. It uses a plugboard which we will wire to print the first 60 columns of a card. At this point the basic mechanism is working and it reads cards, but the printing is a bit off. We suspect this is a matter of adjustment, since many of the characters are printed properly. The device works with sixty long vertical typebars. These are pushed up to their top position at the beginning of a card cycle and then allowed to drop, being stopped by solenoid activated levers that hold a bar from moving further downward. To add to the complication, the typebars have four vertical zones. These are for columns with a 12 row punched, an 11 row punched, a 0 row punched, or none of the above. Thus the characters A-I are in the topmost zone, J through R are in the second zone, /, number 0 and S through Z are in the third zone, and the digits 1 to 9 are in the fourth zone. Oddly, 0 is not part of the numeric (fourth) zone. Once the bar is held in the 12, 11, 0 or numeric zone, further timing lets it drop so the solenoid can now select which of the nine values in that zone are printed. The proper zone is always selected but often the value within that zone is off by one. That is, a card column having A will select the 12 zone but the printed character is B not A. We don't have an adjustment manual for the device which complicates the task of figuring out how it should work and why it is misbehaving the way it has. This is a low priority restoration meant for spare time or bored team members. Carl