HP-41CX fullnut strange issue


My belove HP-41CX begin to do freegames! 2 months ago i remove the batteries and put the calc in a closet. 2 days ago i put new batteries in it and i get that :

2 beeps
and the calculator is blocked in PRGM mode
all keys i push rapidely close the diaplay and i get a "memory lost" message

I cannot "off" the calculator; i need to remove the batteries.

The battery contact are shinny new and the plastic post looks to do a good job (i don't open the calculator yet)


crying Michel

Edited: 20 Oct 2003, 1:20 p.m.


Hey, Michel;

just for the records: is it a full- or a half-nut?

If it is a fullnut, chances are you have some sort of problems with posts and/or bad contact between the mother-board and the keyboard. I have also seen some related symptoms when a RAM/ROM chip is faulty or with bad connection as well.

If it is a halfnut, I'd check for broken connections and/or cold soldering, too.

Let us know what happens next.

Bonne chance!

Luiz (Brazil)


HEY HI LUIZ; i lost your email months ago; i hope you remember me my friend!

I have a lot of questions for you about my newer programs; can you still answer them via email?

For my CX; you know i love it since it's a full nut; but i used my normal 41-c for months and when i need my CX it wasn't working good... Do you think i need to open it? You know, chances are that i will broke a plastic post for ever no?

I know it's better that not working in good cosmetic condition ut is there some kind of soft/hardware things i can do before that operation on a 25 years old calculator.

By the way, how can i know the magnufaturing date on my CX and c with the serial?

Thanks and email me!


Hey, Michel! Good friends are never forgotten... And yes, let me know what you need. Just let me find some time...


Be my guest... as always.

I'm finding a bit of free time for these days, I think that in about two weeks I'll be back to the Forum Daily activities. I'll post a brief about these activities, because they involve Linux, Data Acquisition and HP calculators. As I believe others will be interested on these subjects as well, I must also confess that I'll need some advice in some particular matters.

Best wishes, my friends.

Luiz (Brazil)


I took my HP-41C and the 41-CX apart and exchange the CPU board : The 41C board is working ok in the 41CX case but the 41CX board not working at all in the 41C case.

The 41CX board in is original case : i can sometime get some 0.000 screen and make a fast calculation but in a second i get "MEMORY LOST" and a second after i get the "goose" and the anonciator "PRGM". After that all key i push i get an instant "MEMORY LOST" and a accompaging Beep...

I'm sure that it's on the CPU board and i'm sure it's repairable BECAUSE i get ok 1 or two seconds every hour... ;-(

Thanks for any tips!



Michel, I am so sorry about your broken HP-41CX calculator. Those of us who love them, really do love them. There is a firm: fixthatcalc.com that advertises to repair the HP-41CX for a flat rate fee of US$59.00 plus cost of parts (logic board in your case, I think) and actual cost of shipping. It might be worth your while to check them out. I don't have any experience with them at all, so I cannot rate them for you. But it would at least be a place to start. The very best of luck to you, Michel.
Regards from: Jim Chumbley


Jim --

Many thanks for listing the website! I have an intermittently-functioning 1984 fullnut 41CX that is cosmetically real good, and which I believe is repairable for a reasonable price -- hopefully just a bad connection, and not a bad chip.

I think I'll give them a try.


One thing that brings back a lot of flakey HP41 CPU boards is to clean the card with 91%+ isopropyl alcohol. Scrub it well with a toothbrush, rinse with more alcohol, and repeat. Shake it well, and let dry several hours. Many of these CPU cards have some hand soldered components on them with old solder flux residue. Others have some kind of invisible contamination. Both things seem to interfere with the low current CMOS chips.

Keep the alcohol off of the calculator display window. It will leave a stain...

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