HP-41c display problem


Dear friends,
I have recently aquired an HP41c, tall keys model, from 1980.
I decided to replace the display because, the bottom half of the whole display characters looked a bit dim (just lightly).

As I replaced it for one similar (same aspect but working properly) I realised that the characters are not shown at all except while you keep pressed the key. In this case it is show correctly, but it disapears when the key is relieved.

I have some doubts about if the top left connection between the display and the board should be connected. I have to say that in the replaced display it wasn´t.

Many thanks on advance for your help


1) Only three connection points on the left side group for all drivers.

2) You installed a revision G display driver hybrid into a machine that had a revision F display driver.

3) Change capacitor C2 on the processor board from 0.01uf to 470pf to be compatible with the rev G board. Location shown below in red.

Thanks to Geoff for the original photo.




many thanks for your detailed answer.

- I have connected only three lines in the top left side of the display (leaving free the most left one). The continuity in the connections has been tested and is OK.

- The board already implements the suggested 470 pF capacitor. If it helps, I can see in the reverse of the board the following: 01303L; 00041-60001; J-1935.

- I have tested the calculator with two 41c boards with the same 470 pF capacitor, so the capacitor is fine.

-I still makes the same: it displays perfectly while you keep pressing the key; it gets blank when you release the key...I am getting crazy!!

Many thanks again in advance.



Hi again,

I enclose some pictures in the following Dropbox public folder:


I hope it can be of help

Many thanks!



From page 7 of the service manual's updated service notes (HP41C-35)

4. Display lit only when a key is pressed (blanked in standby).

a. Replace display driver hybrid. (P/N 00041-60090)

Hope this helps,



Bruce: You are ABSOLUTELY right... I have changed only the display driver only in the defective LCD dispay and WORKS fine! It seems that it was faulty (the display driver, not the LCD display itself) as I was thinking it was strange that all the bottom half of the display looks dim...

I wish this experience can help any other collector.

Again: Thank you ALL very much for all your time and efforts to help me.

Kind regards


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