HP-92 printer problem (not the gear)

[teenix]

It would seem some printer related component has failed after a bit of use. However, the problem appeared as the paper was being fed into the printer. Does the hum stop if the paper is removed?

It may have a switch or wiring problem but this appeared to work properly while trying to feed the paper. While not 100% accurate, slowly pressing and releasing the advance switch should give a definite click sound. The HP-97 service manual has procedures for testing the wiring and switches.

Do any of the IC's get warm after being on for awhile, especially the PICK - large black horizontally mounted chip under the printer board. If it is warm it might suggest a faulty IC. Even if not warm, it is possible that the PICK or a ROM has failed.

If the printer motor is the humming culprit, perhaps disconnecting it from the printer board might help, although it will probably not be the actual problem. You cannot leave the printer board assembly disconnected because there are timing components on it and the calculator will not work without it.

Capacitors often fail in old equipment, so it may be one in the power supply, although the calculator itself seems to be functional, or the one on the back of the print motor.

cheers

Tony