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Just a quick question: Does any HP-41C/CV/CX FULLNUT have a separate CPU board and, vice versa then, does any HALFNUT just have a single board? What about FULLNUTs that have been repaired and "became" HALFNUT during that process?
Thanks for your time!



the keyboard PCB and the LCD module for the halfnut (newer) and the fullnut (earlier) are different from each other. I have both types: HP41CV full- and halfnut. There is no way to use the main PCB of a fullnut with the inner circuitry of a halfnut. The halfnut LCD module contains ROM and RAM, while the uP is in the keyboard. All of these are in the main PCB of the fulnut.

Hope this clarifies.


Hi Luiz!

Thanks for the comprehensive answer to my question! And, yes, it helped to clarify things :-)


The Fullnuts have a separate CPU/logic board. The keyboard PCB in a Fullnut is just the keyswitches, and the display driver hybrid is soldered to one edge of this PCB. The display driver hybrid is just the display driver. The CPU board contains the CPU chip, ROM, RAM, PSU chip, timer chip (in a CX), and so on.
The halfnuts have everything on one PCB. The CPU is a surface-mount decive solderd to the back of te PCB, under the keybaord. The display driver hybrid now also contains the ROM, RAM and PSU circuits.
Halfnut CXs have a little hybrid PCB mounted across the back of the main PCB, over the CPU. It cotnains the extra ROM, exteded RAM, and timer circuits. Alas, the ROM code in the dispay driver is different between the CV and CX, so you can't upgrade a CV just by adding the extra PCB.
AFAIK, no fullnut was ever converted into a halfnut by HP. To do that you'd have to replace the entire top case (including the PCBs). Just about all that's common between the fullnut and halfnut models is the bottom case and I/O assembly (the flexible PCB that connects to the modules and the battery pack.

Hi Tony!

Thanks a lot for the many additional information. After digesting your input, I think my original question is now fully answered: If I do understand you right, then merely the Fullnuts do have a separate board indeed. Also, thanks for the very interesting information on Halfnut CV vs CX! As for the Fullfnut -> Halfnut conversion: If I don't mix up things, I believe a certain source of information (that I do not remind at the moment) stated that Fullnuts were occasionally converted into Halfnuts by HP service during a repair. However, following your explanation I think that you're indeed right and HP never did this as it would have made no sense, so to speak. Thanks again for your input.


Hi, Jurgen;

in fact, after the fullnut being off-line, any fullnut sent to be repaired by HP was simply "replaced" for a new halfnut.

What was somewhat discussed here (at least by me) was the original and rare HP41C in a halfnut version. When the halfnut series were launched, the HP41C was no longer in production. Anyway, some exquisite HP41C in a halfnut case replaced original, non-operating fullnut HP41C's from HP "headquarters".

I believe this is a somewhat rare HP41 series model: an original HP41C halfnut.

My US$ 0,10 (how much is this in Euro?)


Hi Luiz!

I do understand your point. Besides, I do agree with you in that the HP-41C Halfnut probably would be a very interesting collectors item. Btw, 1 Euro is almost the same as 1 US$ (currently 1E approx. 0,997US$ I think). Many thanks for your inputs again ... and a general and sincere "thank you" for your valuable, untired efforts on answering questions and providing help on this great forum :-)

Best wishes, Juergen