my 41cv (second pice,buyed on eBay last week) didn´t response. It works only three hours after cleaning the contacts of the battery. Starting with "backspace" after reconnnect the battery for one day - but no responce.
can somebody help me ?



it seems you’ll have to open the calculator and start a cleaning procedure. In most situations like this, bad electrical contact between BATT/IO assembly (where batteries make contact and modules are attached to) and motherboard is the like to happen. I would suggest doing this only if you have at least a few previous experience with electronics or calculators. I strongly suggest having a look at http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=2.

In the first photo of the article, you'll see the upper half of the calculator with the BATT/IO assy. Aligned with it, in the lower half, a series of contacts. There MUST exist the best possible electrical contact between them. But I must warn that opening and MOSTLY closing back an HP41 needs careful attention (screw posts, back-case screw holes, etc.)

There are some cleaning procedures I normally use. Sometimes a single swab moisted with alcohol is enough. If not enough, metal polisher (small, small amounts) will clean up the mess. Also, look out for batteries leakage. They are dangerous...

The other possibility runs around the logic board, if yours is a fullnut. If yours is a halfnut (in the article mentioned above, the CX is a fullnut), no logic boards and no other between-boards contacts.

Hope it helps for now. Let us know about your little fella.



Thank you Louis for answering ( sorry for bad english).
I opened the 41cv, cleaning the contacts but no reaction.
The last in display was 00 REG 290 I think, when I push the ON key.
When the calculator is open and lies on the "keybord", there are contacts to the display in three groups -
four - eight - four. The left four-group has only three wires ?
Now I will open it again and try another cleaning.
Thank you answering.



Yes, it's correct. There is an unused pad for contacts (generaly it's clean, golden surface, no solder on them) at the left-side.

If you want to (and be sure that there is NO RISK AT ALL) you could try openning the other calculator. PLEASE, IF THE CALCULATOR IS WORKING AND YOU ARE NOT SURE ABOUT OPENNING IT, DON´T DO THAT AT ALL!!!

That would be only to test if BATT/IO assy would work on each other. I have three 41's, all working, but I had to change their guts with each other many times to check for what is going fine and what is not. ALL AT MY OWN RISK, so think a lot about it before trying.

And yes: if you had to use metal polisher, remove any excess with alcohol. Carefully. And the zebra-connector between the logic board and the LCD/Keyboard (fullnut only) calls for special care, right?

Cheers. And keep in touch.


I have opened my second 41 so I couldt change the parts to locate the mistake.
It was the battery-conection that failed. It was durty with battery-liquid ( I didn´t know the right word).
I cleaned it a second time and now the calculator runs !!
Thank you for helping.



Hello, Heiner.

Die ist gute Nachrichten! (Hope it is spelled correctly...)

Everytime I get this results, I feel fine with myself. About batteries, I normally see the term battery leakage.


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