Display of HP 41CV is weak


What have I to do? The display of my HP 41CV fades if the view angle is 90 deg. from top. If I look from the front side by about 30 deg. the contrast is as it should be. The fading figures are partly shown better or worse. All information words USER, PRGM or ALPHA are weaker as the main display.

I changed the battery and thought that the problems have been solved. But after some days they started again. Slightly increased temperature makes the display unusable besides I look on a very flat angle.



can you identify if it is a halfnut or a fullnut?

This image is from the HPMuseum.

Although it may not solve the problem itself, the halfnuts allow contrast changing through specific commands, available in some custom modules.

Not much of a help, sorry.


Luiz (Brazil)

Edited: 19 Aug 2006, 9:14 a.m.


Hi Luiz,

it is a fullnut original hp display. My first idea was also that there might exist a special command. If I cool the calculator by some deg. the display is much better. So there might be another additional effect included.
Thank you for your response!


Hi, Bernd;

the fact that the LCD contrast enhances with low temperature leads me to think of an aged LCD. Earlier HP41 units had an (yellowish) LCD where one could see the complete set of segments with the calculator turned off, by simply finding the correct viewing angle. Newer units had a better LCD.

I remember repairing an HP41 with a very dimm LCD, one could barely see if the calculator was ON. I measured a current consumption higher than usual when it was ON, causing batteries to be drawn too fast. Then I decided to replace the LCD driver for another one taken from a dead HP41. If I am not wrong, it is a hybrid IC, with some bipolar transistors. It worked perfectly fine after that. I still have the deffective LCD driver, but I actually have no clues about the existence of any direct (or adaptable) thridy-part replacement.

I hope you succeed.


Luiz (Brazil)

Edited: 19 Aug 2006, 5:19 p.m.


Hi Luiz,

thank you very much for your information. The display seems to be a newer one. Can you remember what the normal current consumption is? I would like to start at that side as well.

There is another effect which might correlate to that problem: Replacement of the batteries is difficult. I have to knock from a corner until the display gives reaction. And if I switch OFF and ON again it is still OFF. After some tries everything works well and is reliable - besides the display. The battery contacts have been polished and no corrosion could be detected. I am not so far to open the case because it is still operable - and I like it! May be I have to buy a dead HP41 to get more experience.

I am really exited that it is possible to find people with experience on that subject.
Many regards from Germany


Hallo, Bernd;

I am really excited that it is possible to find people with experience on that subject.
I'd go ahead and tell you that this is the very best 'e-place' to find them. I found a lot of usefull information here, believe me. I like contributing, but there are others that know much more than I do. Viele danke!

About the HP41 internals: just to give you a glympse of what exists, have a look at this page (it may take a little while to load all images; depends on your connection spped). Dieog Díaz designed and produces the Clonix/NoVRAM/NoV32 modules that are fully compatible with the HP41 IO structure. The pictures you see are from the many boards found in the HP41 series. The chip I mentioned (LCD driver) is the one seen in the right side of the board identified as 'HP41C/CV Common Board (CV Version)', in the third row, first column. You can see it again in the picture below it: 'HP41C/CV Common Board (C Version)'. The other two pictures at the right side if these ones show two versions of the mainboard used in the CV/CX fullnut, named 'HP41C/CV/CX Common Board (CV Version)' and 'HP41C/CV/CX Common Board (CX Version)'; in these boards, the LCD driver is in the left side of them. Anyway, in all of them, the LCD driver has an ID code of the type 'RAYLnnnn' or 'RAYCnnnn' (the 'nnnn' part refers to a four-digit number).

About the current consumption: at the time I had the mentioned HP41 with dimm LCD repaired, I posted about the measurements. I did not locate the post, which leads me to think that I actually added it as one in an existing thread. In this case, please give me a few time to collect these values and I'll post again. Right? Maybe, meanwhile, someone else does it... People here are very friendly, help is always comming.

Best regards.

Luiz (Brazil)

Edited: 21 Aug 2006, 12:23 p.m.

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