HP-41CX damage from battery corrosion...


Hi there,
I just picked up an HP-41CX from eBay with the battery contacts of the machine corroded. If I get to keep the machine, is there any way to tell if the battery acid/base might have spread inside? Does anyone know if there is a fairly easy way to open the machine without breaking anything? If the machine works now but the liquid has spread inside, are there significant chances for the machine to die soon?
Thanks in advance,


Andreas --

If I remember correctly from earlier postings, you bought a halfnut, whose internal components (display, keyboard, CPU and other chips) are integrated onto a single board -- even in the CX, I would assume. Halfnuts are generally more difficult to repair than the (older) fullnuts, although that may not be relevant to this problem.

On any HP-41, separate the case halves by removing each of the four rubber feet, along with their adhesive backing, and the screw underneath. Then, you'll be able to see how far the corrosion has spread.

If it is limited to the battery terminal contacts, one Forum participant has developed and fabricated a replacement "foil" for sale. The individual and the details can be found in Archive #15.

-- KS

Edited: 13 Mar 2006, 12:28 a.m.


Hi Andreas, and thanks Karl for the reference...

... may this link be of some help too, it's just four threads below:


Best of lucks with your CX.



Thanks Karl, Diego. I read somewhere that after I put an HP-41CX back together, if I tighten the screws too much, I'll either destroy it or it won't work!!! I decided to refrain from that for now, and if the machine fails at some point, to take it apart then, or send it in to FixThatCalc. I'll consider the FlexPCB at some point.


The Halfnut does not have a separate logic board, so it does not need the case's pressure to work. Disassemble it and clean it, it is no big deal! Do not apply force when tightening the screws and it will be easy as 3,14159!

Greetings, Klaus


Thanks for the insight. Do you know if I should use baking soda and water for cleaning?


I do not know whether baking soda is harmful or not. I always use agua demin. (distilled water), and a Q-tip or a piece of cloth.

One more warning: static electricity! I never had any problems with that, but make sure you ground yourself before opening the calc!

Good luck! Klaus


Klaus, your help is much appreciated.

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