HP 41c card reader repair

[Johnboy]

Hi All,

I have a bunch of 82104 card readers I am repairing at the moment, most so far are just the roller. I am using silicon rubber tube for the new roller that I mill down to size using a drill press. I am getting pretty good at this, and last night I did a roller replacement from start (opening the case) to finish (testing the card reader) in under an hour.

There's something I noticed last night that I though is worth sharing. The roller in last night's repair was not so much gummy but "crusty", like hard crusty, so much so the roller would not even turn initially. I noticed that if you pull the motor out when the roller doesn't turn you risk pulling the worm gear off the motor shaft. I was wondering if this might be a cause for loose worm gears, a problem that seems pretty common. My solution was to use a small screw driver to lever the end of the worm gear, which in turn did rotate the roller enough to get the motor out undamaged.

I also wanted to ask the brains trust here about failed capacitors in the 82104. I see to recall there is a cap that can fail, but I can't find any reference to that in recent repair postings. The only information I have is that the cap is near the sense amplifier. Does anyone have any more information on that. I have one card reader that has MALFUNCTION or CARD ERROR despite my best efforts to repair it, which made me thing of the cap.

Cheers,
John