HP-41 CX



I have bought a HP-41CX halfnut with faulty working "user key". Sometimes it works sometimes not. Don´t worry, I knew it and I got a very good price (good seller).
May be somebody knows if it can be fixed anyway.
I have also a 41CV halfnut. Could I use it´s keyboard for the 41CX?. If it is possible, can I change the "HEWLETT PACKARD 41CX" logo from the original to the CV`s keyboard?

Thank´s in advance



You could also use SF 27 / CF 27 to get in and out of user mode... :)



Oh God!

I didn´t realize there is another thread for the 41 keyboard repair. Anyway may somebody has an special solution for the user key.

Thanks to Massimo for the alternative. It is a good idea if can´t repair the contact


See the threads on HP keyboard repair. The user key is just another key on the keyboard. Its' contact is easily cleanable using the "wire brush" technique.


David has a good first idea. It may just be me but i have had more dirty on/user/prgm/alpha keys than any other and they can be cleaned out. Be gentle.


The problem was the plastic foil under the batteries. After cleaning the key several times with isopropilic alcohol I didn´t get any result until I forgot placing that foil. It seems this element produced any bad contact. So I made the hole for the contacts 1 mm wider and now everything works. YAHOO!!! (and I have the cleanest user key of the world).

This is the first time I open a halfnut. Although it works fantastic it seems it has been serviced. There are two diodes and a capacitor soldered one over the other on one side. I see also red wire connecting two points. Has anybody a photograph of one of these calcs opened. In the main page I have only found a fullnut inner photographs.




I posted a photo a few days days ago showing an opened (dismanteled) halfnut and these components are present in at least eight halfnuts I have already opened (two CX and six CV). You may also notice that earlier halfnuts have a post-production cut in the cooper trail where the red wire is soldered, while the newer units have this trail already separated in the PCB layout.

I've been served by a provider that does not care a damm dot for its customers, so the page I was using was removed and created again and all my pictures are gone. I'm lucky I have all of them, so I'll have to upload them all back.

If you want, I can e-mail you the image so you can check if yours is the same type.

Best regards.

Luiz C. Vieria - Brazil



look at the picture below:

The extra black&red wires in the top of the image were added to test the unit with an external battery pack, they do not exist in regualr units. I don't know how long will it survive again, so if you like it, copy it to your HD...


Luiz C. Vieira - Brazil

Edited: 21 June 2003, 12:00 p.m.



would you be so kind to reload the picture about the comma/dot jumper on the spice series?
I wasn't fast enough and couldn't see it...

Thanks a lot,


Hi, Massimo;

long time, no "read"...

Here it is:

I'm organizing the images so I'll keep them in one directory in my working HD. If (when?) it happens again I'll quickly put them back. I'll "collecting" them around because I have four computer connected to each other (my own home net) and there are at least 3 hard-disks where some images are stored...

Thank you and best regards.

Luiz C. Vieira - Brazil

Edited: 21 June 2003, 1:27 p.m.


Thank you very much, Luiz!
Now I've stored it on one of my PCs too... it will hardly get lost again ;-)



The diodes and caps and wires are standard construction for the halfnuts.

BTW, when opening a halfnut be very careful of the speaker wires. They just LOVE to break off the circuit board.


Thank you.

I see it hasn´t been modified. It´s no the best design I have seen from HP.



I never met an hp41 speaker wire i could not do without. The only time i ever used the noise function on purpose was to set up my 41 with the ppc rom to be a piano. I handed it to a friend who plays keyboard. He hit all the keys once and proceeded to play "Mary Had a Little Lamb". OK, it wasn't Mussorgsky's "Pictures at an Exhibition" but i was impressed.


Maybe that's because when we first go to the machine, we turn it on and whatever bits are on our fingertips fall off and into the gaps around the On/User switch.


It has gotten no worse since i started to keep the calc in a baggie. With that tidbit it makes even more sense.

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