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

[rprosperi]

I recommend you replace the coupler (incorrectly called a clutch in many posts) whenever you replace the rollers of a card reader. Often they initially seem OK, but are actually aged and drying inside. If you skip replacing the coupler, the newly repaired rollers will move cards with no problem and the reader will initially work ok, but soon after the reader will stop reading/writing properly as the new activity with the dried coupler starts to slip. I've read of this happening more than once and recently had the exact same situation, fixed by Geoff, confirming my suspicion of the cause.

[AndiGer]

John,

Did you find this thread in the museum's archive?

https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=145348
In Message 16 Ignazio Cara described where to find the 6.8µF capacitor in question.

Please report it fixes the problem for you as I also have a card reader that reports MALFUNCTION or CARD ERROR most of the time, never reads a card (but worked in the past). After some read tries maybe I get NO ROOM. TRY AGAIN.
Sometimes the card read messes up the whole 41 and I must force a MEMORY LOST.

Andi

[ThomasF]

Hi!

Has anyone tried the Service ROM for the 41 together with the card reader?

I have not done it (at least not yet), but I noticed when going through the code, that it tests e.g. the speed when reading, and it looks as if it gives a indication if too fast or slow (in %), and it can also return some count of the motor speed.

It also detects CRC errors etc, so it seems to be quite a good test suite for the card reader by the look of it, especially if one is trying to trim the motor.

The service manual (found on Eric's manual site) describes how to use the test (page 43-45 in the PDF).

I could give it a try and get back with my findings.

Cheers,
Thomas

[Johnboy]

(09-25-2024 03:24 PM)AndiGer Wrote:  John,

Did you find this thread in the museum's archive?

https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=145348
In Message 16 Ignazio Cara described where to find the 6.8µF capacitor in question.

Please report it fixes the problem for you as I also have a card reader that reports MALFUNCTION or CARD ERROR most of the time, never reads a card (but worked in the past). After some read tries maybe I get NO ROOM. TRY AGAIN.
Sometimes the card read messes up the whole 41 and I must force a MEMORY LOST.

Andi

Thanks, that's exactly what I was looking for.

[Johnboy]

Since my original post I have successfully repaired 6 out of the 7 card readers I have. The repaired ones all read/write and respect the protected cards.

The one remaining card reader is problematic, giving me "card err" and "checksum" error messages when reading a card. By swapping parts with one of the good working card readers, I have deduced that the problem is not with the electronics (bottom half of the card reader), but with the motor / card receiver unit. I have changed the roller and given it a good clean, and run the head cleaning card through a few times but still the same errors occur. I just happen to have a spare motor/card receiver unit (condition unknown) and when swapping that one in, I get same/similar errors.

I find it strange that known good electronics doesn't work with the both of the motor/card receiver units I have.

Unless anyone has any suggestions on what to do next, I am going to disassemble the card receiver units and check the switch contacts and pcb tracks. The only other component on that unit is the IR led receiver, can they go bad ? and I thought that was to do with "protected" card detection anyway, shouldn't affect reading.

Any further information/suggestions appreciated.

Thanks
John