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I seem to have a cursed hp41c card reader...please help.

The card reader works perfectly on my hp41c but when plugged into my hp41cx the calculator would either not recognize it or would go crazy and not respond until I unplug the card reader. The port 4 of the hp41cx works properly with modules and other peripherals but somehow rejects the card reader. Could the card reader be cursed by the previous owner?

Thanks in Advance



the first things that come into mind are contact foil/spring problems, and/or battery/energy problems.

Maybe one or more of the contact springs of your card reader has a slightly different (out of line) resting position,

which may still make good contact to the foil of your 41C, but not necessarily in other HP-41 units.

Or the energy side: Did you try with the same battery pack in both calcs when using the card reader?



Hi Fouad,

even though port 4 works properly with modules, the card reader uses a unique address not used by modules. So there may be contact problems around port 4.

Hope this helps.


I have tried changing the battery pack but still to no avail.
I forgot to mention that even though the calculator does not recognize the card reader but when I plug a card in the reader the display shows weird things and freezes.

I will attempt to clean the contacts inside the calculator and get back to you.