HP9810A Printer

[Paul Berger (Canada)]

Does the motor turn freely with not power applied? From what I gather the motor is a stepper motor, you should be able to turn it pretty easily. If it does not then it may be that the bearing is partially seized or there is some damage inside, if the idler gear is engaged make sure the teeth are clean on the gears, dirt in the bottom of the teeth can cause them to bind, the idler gear could even be seized. If it turn freely then I would start looking at the stepper drive electronics. It looks like the drivers are discrete transistors as per Tony Duell's schematic found on hpmuseum.net. Failed components here could cause the motor to not turn and even to chatter if it cannot advance a phase. You might also want to check the motor for open windings.

Paul.