CONTINUING RESTORATION OF SELECTRIC BASED CONSOLE PRINTER FOR 1130
The IBM 1130 comes with a console with a keyboard and a typewriter, along with some switches and controls. The keyboard is not connected to the typewriter at all, it is the keyboard from an IBM 029 keypunch mounted into the 1130. The typewriter is an "I/O Selectric" printer only device. This is based on the original IBM Selectric typeball typewriters, but with solenoids, microswitches, pushbuttons and mechanisms added to allow this to be driven by a computer.
Because of the additions to the basic Selectric design, many components in the machine are blocked from adjustment or direct access by the layers of additional hardware that were added to make it an Input-Output (I/O) version, in this case a print only type. That often requires substantial disassembly of parts to gain access which on a regular consumer typewriter would be easily reached immediately.
The oil and grease used in the 1960s will slowly absorb dust from the air and become solidified. The foam sound insulation inside the case looses its plasticizer and reaches one of two states - either a crumbly powder or a tarry goop. In many cases, it does both in different parts of a machine. The result is a dirty device which has most moving parts frozen in place. They rarely work if they have been sitting for years, requiring substantial labor intensive cleaning to restore operation.
FRONT PUSHBUTTONS WERE MISADJUSTED
The operator of an IBM 1130 has to be able to space up the printout in order to tear it off. They also need to be able to set and clear tab positions. Finally, a means is needed to move the carrier over to a chosen line or to activate the tab function, when the operator is setting up the typewriter to print a form or designed output.
IBM added three buttons on the front panel - Tab, Space and Return - to trip the operational section functions that accomplish those tasks. The buttons pull on a wire inside a metal jacket since the selectric operational unit triggers are at the right front of the machine and too close together to have buttons in between them. The wire cable routes the pull from the centered pushbuttons on the panel over to a plate in front of the operational unit triggers, ultimately rotating and moving a pad down to push on a trigger and trip it.
The current adjustment had those pads moving down in front of the triggers, failing to activate them. The parts that must be adjusted to correct this are behind a plate and behind all the parts anchoring the cables, holding the arms with the pads and attaching springs to control their motion. I had to disassemble the plate, detach the wire cables, and disassemble the pushbuttons in order to get inside and adjust the moving arms with the pads.
Once they were adjusted, I reassembled everything and verified that the pushbutton will now reliably trigger its operational function. Of course, I had to free up the gummed oil to allow all the parts to move freely weeks ago, before I began to address the failure to trip the functions when pushed.
ITERATIVE PROCESS OF FINDING PARTS THAT SHOULD MOVE AND FREEING THEM
The machine has several thousand parts, many of which have to move. It takes patience to examine everything and find each part that must rotate or slide. I use an extremely fine clock oil to soak in under the frozen lubricants so that I can move the parts. Exercising the parts after application of the clock oil is necessary until the normal range of motion and ease of movement is restored.
The margins on a Selectric are set by sliding two parts left or right on a bar. These parts have a long blue plastic indicator on the front which shows through a plastic window on the front panel, to indicate the current column for the left and right margins. They should slide easily when the blue part is pushed back to disengage a tooth from the rack they slide upon. It took quite a bit of work to unstick these but now they move freely.
MAINSPRING BROKEN
The Selectric typewriter receives power from an electric motor which turns a shaft in the machine. Various clutches will engage with the shaft to move parts when a function such as tab is required. Another clutch will engage with the left side of the shaft to produce one print cycle - selecting a character on the typeball, striking the ribbon with the ball, advancing the ribbon and tripping the space to move right one column.
However, the rightward movement of the carrier is not driven by the motor or shafts. A mainspring is wound up as the motor pulls the carrier all the way to the left in a carrier return operation. The tension in the spring pulls on cords running to the right side of the carrier, trying to move it rightward.
The carrier is held in place by a tooth that engages a rack running across the typewriter behind the carrier. The tooth is temporarily pulled out of the rack when a space operation must take place, allowing the mainspring to begin moving the carrier rightward. The tooth drops into the next spot in the rack so that the carrier has advanced just one column.
The tab operation pushes the tooth away from the rack and latches it way. This allows the mainspring pressure to slide the carrier rightward rapidly. A projection on the tab mechanism on the carrier will bang into a metal point if the tab is set for that column, releasing the latch and stopping the carrier. A cylinder runs along the rear of the machine with a metal point at each column position. The point is moved by a tab set or tab clear.
The clear symptom here is the lack of tension and no movement of the carrier to the right when the tooth is released for a space or tab request. I had rotated the spring housing when I installed it but with a break in the spring metal inside the housing, it provides no force. Carrier return does not wind it either because of the break. The spring itself is a long band of metal which should be fastened to the outside of the housing on one end and bound by a notch in the axle on the inside.
I have a new mainspring on order. When it arrives, I will install it and pretension it.
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