REPLACED - CARRIAGE STEPPER NOW MOVING
I had found some GM Delco 2N392 transistors on eBay - apparently this was used widely in car radios. The first new-old-stock transistor arrived and I installed it into the plotter. When I powered up for a test, the ring counter was restored to correct operation. The manual control for carriage right or carriage left now shifts the ring counter one step, changing the coil that was activated and moving the stepper motor one position.
WAITING ON PEN SOLENOID TRANSISTOR TO REPAIR THE REMAINING CIRCUIT
The second new-old-stock transistor is on its way from a different vendor. Once it arrives I can stick it into the pen flip flop circuit and finish restoring that to (hopefully) full operation. However, having done some circuit testing and analysis, I am concerned that another PNP transistor in the circuit is also bad.
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