HP9810A Printer

[aj04062]

So I finally got around to repairing the platen on my 9810A using the 3M cold shrink. After all of this, the motor doesn't have the power to rotate the mechanism. Rotating by hand seems hard, but can be done from the motor pulley.

When installed into the machine, and the paper advance switch is contacted, the motor makes a stuttering noise, but does not rotate.

Is there a motor issue here or should this mechanism rotate easier? I've taken it apart a couple times to make double check and I even have another unmolested (but gooey) unit to compare against.

Suggestions?

[aj04062]

I took off the main gear that drives the printer mechanism to test if the motor had any torque. It didn't even turn the idle gear. There must be something up with the motor.

I tried another printer unit I have and this one seems to advance fine so there isn't an issue with the main calculator's circuits. I have not ruled out the PCBs on the printer mechanism.

Anyone have similar issues with the motors on these?

[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.

[aj04062]

Yes the motor turns and the gears/belt seem fine. Sounds like a stepper motor or drive electronics issue. Thanks for the clues! I'll see if I can identify.

[aj04062]

Thanks Paul,

I changed out the print head board on the printer that was not advancing. That fixed it. So something is off with that board. I made a note on it, but probably will not address it as I have a parts 9820A I pulled from.

I have another issue I'm trying to debug. The machine had a cup of coffee or something spilled into it right where the pacs go years ago. I couldn't get one module out, so I disassembled and once apart, I could get it disconnected. I've washed the board down, dried it (canned air, hairdryer and time) and re-assembled. I've got the machine 100% working (printer, card reader) so I wanted to let it sit and run for a while to make sure nothing acted up.

Well, with this module board plugged into the back plane, after 10-20 minutes, the display starts to flicker random numbers and the machine becomes unresponsive. If it is shut off and turned back on, the display does not come back. If I unplug this module/daughter board it seems to be fine and stable. There are NO components on this board. It is just connectors and a PCB.

Could there still be gunk on the board creating an artifact that corrupts the memory? It looks clean, but I cannot see under the card connectors.

EDIT:
Perhaps there was a bit of moisture still there as I have re-assembled and it seems to be fine....Or perhaps a flaky connection that improved after taking apart 3-4 times!