Problems concerning HP 82104 card reader


I had plowed through all previous posts, but unfortunately none of them matched the symptoms of my HP 82104 card reader. (That of HP 41C)

After replacing the original gummy wheel with a pair of o-rings of 3mm ID and 6mm OD, I put a card in but it did not go through. The card seemed to be stuck and the black gear (that had two o-rings on) stopped rotating while judging from the sound, the motor was still spinning.

I took some little experiments and found out that when I put a card in slightly after triggering the "on" signal but before it approaches the the o-rings, the black gear spins freely. However, if I push it in any further, it gets stuck.

Does this phenomenon implies that I should use smaller o-rings or there are flaws in the clutch mechanism? If so, what should I do?

Thanks in advance!

P.S. Please inform me if videos are needed.



I assume you have already red this thread as well, so the correct external diameter pointed out by Randy (last follow-up) should be 6.35mm.

Also, there is the pulling gear issue. It's been discussed some points about how should the pulling gear be connected to the motor shaft, and the use of flexible, silicon-based glue or rigid glue has been considered. In any case, chances are that the gear is not firmly connected to the motor shaft if it is spinning freely. I could not locate the other threads about this subject.

Not so much of a help, sorry!

Luiz (Brazil)


Thanks for fast reply!

I had read that thread, as well as many others (e.g. this one ) that indicate 1/4" OD o-rings. I got 6mm ones merely because they are of the nearest size that sell in a shop in my neighborhood. I'm just wondering that since the card cannot go through with 6mm o-rings, how about 5mm ones?

I suppose the thread you've mentioned to be the following one: Randy pointed out that the coupling between motor and shaft is not clutch in this article, but does that mean the "part of the urethane rubber couple material" as described inolder post here (w/ pictures) (by geoff) should be glued?

(P.S. Turning and twisting the "ECCENTRIC CAM" (The pin that holds the gear w/ 2 o-rings) does not make any difference.)


I think you need to rebuild the coupling.

A drop of super glue will prove if it is slipping or not. While it may work for a bit, it is probably not a long term solution.

Geoff recommended a piece of outer jacket from an iPod headphone. I use that with some small wire insulation and it works great. I usually apply a little adhesive when layering these together.

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