HP41C faulty


My HP41C has a "display" problem in that the display goes blank, when the machine goes into standby mode (ie between key presses). If a key is pressed and held the display shows the key and then the NULL. Also the flying goose is visible when a program is running.
I suspect that the power supply IC is at fault but I don't know where to get a spare should one be available or even if the unit is repairable.

Any guidance would be welcome.



Does the display blank after about 15 seconds??? Try XEQ <Alpha> ON <Alpha>, which disables the automatic shutoff feature. Does that fix the problem? If so, then I believe you have a problem which appears to be common to many 41's.

To fix this, open up your 41 and check the connections between the main board and the LCD driver board (at the top of the machine, beneath the LCD). There are several tabs which are soldered to both boards, and these have a tendency to break and develop intermittent contact.

Being VERY careful, use a fine-tipped instrument to gently pry up on each tab where it joins each board. If it comes up, it needs to be resoldered. Use a fine tipped soldering iron and the proper solder, and good luck.

- Ed


>My HP41C has a "display" problem in that the display goes
>blank, when the machine goes into standby mode (ie between
>key presses).

Try the solution suggested to you by Ed Martin.

>If a key is pressed and held the display shows the key and
>then the NULL.

This is normal.

>Also the flying goose is visible when a program is

This is also normal.




I'd like to help, but I must confess I did not understand the problem.

When you switch the calculator ON for the first time, what do you see? The HP41 normally shows the X-Register contents and any active annunciators, except for ALPHA, PRGM and SHIFT, of course. The only way you have a blank display when you turn the calculator ON is by storing a blank ALPHA in the X-register (at least this is the only way I know), considering the calcualtor is working fine.

Now about yours: you mention a standby mode between key presses. Standby mode is exactly this: after an operation is performed and before the next key is pressed. In this case the calculator should show something: X-Register contents, a message, ALPHA contents, program steps or the flying goose. Yours go blank-display between key presses?

What about these:

- ALPHA mode
- PRGM mode
-after an AVIEW or VIEW nn

What happens in these cases?

If the LCD shows the flying goose and function name + NULL when key is held down, there is something more than bad contact in the LCD's module.

At least it seems to me that is. I'd liek to know a few more about it.

Success Adn best regards.


To Vieira, Luiz C. (Brazil), et al.

I am sorry if I was unclear.

When the calculator is in standby mode ie( turned on, but not running a program) the display shows nothing (just like it is turned off). None of the annuicators are displayed.
If a key is pressed or a program is run the display "lights up" and behaves normally, or at least until it drops back to standby mode.

I hope this helps clarify the situation.

I will try re-soldering the display tabs as suggested.

Many thanks. I will advise as to how I get on.



Hi, Graeme;

that's really new for me. That's the first time I read about this particular behavior.

Thank you for clearing the symptoms. I'm very interested on knowing about the solution, say, if simply resoldering the LCD connections is enough.

Thank you very much. And success!


I have seen this problem NUMEROUS times. A lot of times it is caused by a bad conenction to the LCD module (gently pry on each of the 16 or so contacts and see of any pop off).

Another very common cause is contamination (often invisible) on the keyboard circuit board or back of the LCD circuit board. Clean well with 91% isopropyl alcohol... don't let it get on the display window... it will leave white stains behind.

Can also be caused by a bad LCD module or CPU card... only replaceable from another machine.


Maybe you could try a full reset, before doing surgery. At least a backspace-ON, or leave batteries out overninght. This might not work, but I would try that before touching a soldering iron to a 41 of mine.

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