HP-41 + card reader = "Malfunction" ?



I've got a pre-overhauled HP-41 card reader from eBay that works fine with one Fullnut HP-41C and not with another. I suspect it's a problem with that calculator, but can't figure out what it is. Here's what I've found/done:

- Inserting a card in the reader immediately results in a display of "Malfunction" followed by "Card". I don't hear the motor start at all.

- If the calculator is off, inserting a card can cause the motor to start and turn very slowly.

- A module or printer plugged into to the same physical port the reader uses works fine.

- No other modules installed.

- No other problems noted with the calculator.

- Catalog correctly shows the card reader functions.

History: I had some intermittent turn-on problems with this calculator, which I first tried to resolve by cleaning the zebra connector and all board connectors. Seemed to work for a while but eventually the problem returned. Second try was to re-solder all the display board wires which appeared to permanently resolve the problem.

I re-cleaned the board / module connection again but didn't notice any improvement in the card reader problem.

Any speculations whether this is a calculator problem or reader problem? Any suggestions for troubleshooting?




Have you tried changing out the batteries? The card reader motor pulls more current than other periferals and might not function properly if the batteries are low.


Thanks! I did swap the battery packs. No luck.


If the zebras are the pink elastomer version, that's the problem.


Hello Randy,

Is it a cleaning that is required or a new elastomer strip? If a new strip, any sources other then another calc? Also any sources for the wire wrap connectors?

That is, has the carbon in the elastomer lost its (due to cracks or aging) conductivity?

Thanks, Geoff

Edited: 27 May 2011, 2:36 p.m.


Cleaning almost always makes the condition worse. They need to be replaced with either gold version from another unit. The pinkies have relatively high resistance, usually above 50 ohms when good. They reach 1000 ohms and higher which is okay for most signals but doesn't play well suppling power to Clonix, card readers and other high draw items.

The other cause can be corrosion or other sources of poor connectivity on the battery i/o block to keyboard connection.


Thanks Randy.


This is the first one I've seen, but it looks white to me. After I read the responses I took a look at the schematic and saw that the power for the card reader motor runs through that zebra connector. Ugh.

I guess the next step would be to replace that connector with wires?

Thanks for all the responses!



You could ohm out the circuit before doing something drastic like soldering wires to things...


I'll check the zebra strip and see what I find. But if I do find a bad spot, is there anything I can do about it?

Or is the idea if I don't find anything amiss then the problem is elsewhere?

If the strip is bad has anyone identified a compatible replacement?

Thanks for the help!



thats the problem Bob!

the only solution is to find a defunct 41 (non repairable) and harvest the elastomer or wire wrapped (peferable) connector.

i have tried to find replacements but have been relegated to the harvesting.

no spares I am afraid.



I disassembled the 41 and, contrary to my memory, the elastomer contact strip is of the pink species. A quick check with a VOM showed several spots with high (>1k ohm) resistance.

I saw a replacement flex wire connector on TAS (just the flex part, not the plastic frame), I'm not sure if the plastic frame used for the elastomer strips can be used/adapted for that style of interconnect. I'll probably give that a shot before doing the zillion wire solder job, though.

I'll post if I have any good results.

Thanks Geoff and Randy.

Edited: 30 May 2011, 8:22 a.m.


Just to close the loop on this - I replaced the elastomer strips with a new old stock flex wire strip and that fixed the card reader problem.

Thanks again for the help, everyone.


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