IDENTIFIED BROKEN PART IN CARRIAGE
The knob which switches the platen in and out of engagement with the gear box is shown in the diagram below from the parts catalog, with the parts circled in green. The knob rotates and a pin on the inside turns with the shaft. That pin fits in the notch in the metal fork piece on the top of the assembly to the right.
The next diagram is an exploded view where you can see the piece that has one of its fork tines broken off. It is hooked onto the shaft with a tapered pin.
With one of the tines of the fork broken, the pin on the back of the knob shaft can't move the fork back and forth, twisting the shaft to cause the platen clutch to engage or disengage. I believed I needed to restore the U shaped channel or add back the second tine so that the knob shaft can cause the fork's shaft to turn in both directions.
FINDING THAT SPRING IN CLUTCH OBVIATES NEED FOR THE SECOND TINE
While I was watching the motion of the knob and the fork, considering ways to replace the tine's function, I noticed that the platen clutch would be held out of engagement by the remaining tine when the knob was turned to Out but when the knob is turned to In, the clutch pulls the fork over to engage.
That is, the tine doesn't need to move the fork since the spring force in the clutch assembly is trying to pull it to the engaged side at all times. It takes positive force to disengage, using the remaining tine, but when that force is removed the clutch snaps into operation.
NO WORK NECESSARY, THE IN/OUT KNOB WORKS PROPERLY AS IT IS
I can cross this task off the restoration list since the printer works properly without having to address the broken tine of the fork.
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