Problems rebuilding a 41c Card Reader


I thought I was beginning to understand the 41c card reader, but this one has thrown me a curve. After assembling the reader (and checking it over several times for lose wires, bad contacts, etc) as soon as I plug it into the 41, the motor runs. It will run for about 5 seconds, then shut off. If I attempt to power on the 41, it will not start (display blank). If I unplug the card reader, I can power up the 41. I've tried 2 41's and I have the same problem.

What could be wrong with the card reader to make the motor run as soon as it's attached to the 41's port? Other than the wheel slipping (what I was fixing), this was a working reader until my last repair attempt. Thanks!



The contacts that tell the reader a card has been inserted may need adjusting.


I'll take another look, but I actually went out of my way not to disturb the contacts. What are the chances it's a component failure on the board? Thanks,



That one I can't answer for you. There are others here who are electronic smart


I initially thought the reader motor start contact was closed. A photo of switch points for reference:

I tried duplicating the problem by shorting the motor start contact, but it didn't prove out. While the calculator was dead and would not turn on, the reader motor ran continuously and would not turn off. Different problem than you describe.

I doubt you killed anything in unit as I'm the king of klutz and have never had a reader I was able to render permanently dead.

Still thinking about it...


Hi Randy, guys;

I am not sure, but is there any solid-state switch that would turn motor ON and allow it to go OFF after a few seconds? I think the only common line on it is the "power line".

A few days ago I got the following problem: an HP41 that would turn ON, blink the 0.0000 and than it yould turn off and refuse itself to go ON again. I opened it, clenaed the contacts and rebuilt it. Same problem.

I took the batteries of another HP41 and it did not even switch to NO. I cross-tested the batteries and felt myself confused: the problem was in the batteries.

I tested each one of them and found 1.38 to 1.48 Volts eanch, but when nI tested for current, one of them got less than 1mA, others could go more than 180mA. I placed the "bad" pack back and measured voltage by the small golden balls used for external DC power connection. Voltage was fine till I press ON key: it would drop to about 2.5 V (high resistence from bad battery) while LCD would blink the 0.0000 and then the calcualtor shoot-off. I changed the batteri and everything is fine, now.

What I mean is that electrical connection with bateries is achieved by the HP41's I/O connector, and batteries (+) and (-) lines go stragiht to any external devices. This means there is no way to cut off power to the devices by solid-state control; how come the card reader motor stops working? Are batteries O.K. when extra charge occurs?

Just a suggestion.

Luiz C. Vieira - Brazil

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