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I hope someone can help me out here!I bought a 41C back in the 80s but it sat unused during the 90s.I took out the batteries and the contacts are clean.The other day I tried to put in 4 new N batteries (1.5v each) and expected it to turn on and work again!!!It is completely dead.Any ideas as to what I can do or check.My son would give anything to get it up and working again (for him this time).Thanks!

Hi, Joanne;

considering that the batteries are fresh and properly installed, I'd suggest a "first step" by opening the calculator": four screws, each one under each rubber pad. If your son has skills, let him go for it. Otherwise, experienced people to advise is always recomended. In all cases, make sure electrostatic discharge (ESD) precautions are taken prior to any internal procedure: the MOS circuits inside the HP41 are somehow easily damaged by ESD.

After that, with the calculator opened and both case halves separated, check all screw posts for cracked surfaces or (worst case) broken/dettached post. If so, repair posts. Then, cleaning all contact surfaces is recomended, mainly:
- exposed conductors in flex circuit connecting batteries and I/O module connectors to the mainboard;
- mainboard conductive surfaces related to the flex circuit mentioned above;
- all connectors under the small circuit board that is assembled in the lower part of the calculator, inside the case, below batteries compartment.

Next step: build it back and test again. If no activity is still observed, post a message again; then let's take other measures.

Hope you succeed.


Luiz (Brazil)

Edited: 25 May 2004, 5:32 p.m.

Why don't you try to open it and clear the internal contacts? But before doing this, touch something of metal, to discharge electricity from your body.
In my HPs 41, the base (hole) from the screws in the top of back were broken and I only could see that when I removed the extension ports conector from the back part. So, when removing this part, do it on a table and carefully, for not lose any part and being able to use a super-glue to remake it, if this is the case.

Good luck!


Excuse me for asking the obvious but, as opening,cleaning and closing is not so simple, I would rather start by the reset sequence (keep pressed the CLx/A key and press ON) Try many times, if nothing happens, then an internal bad contact may be the suspect. Just in case, recheck batteries regarding voltage and polarity, and bad contacts on the battery holder.

If you decide to open it, etc., then be very cautious with the rubber feet (to be able to set them back after a successful repair), and also with the screws: any excess force while unscrewing or screwing will damage or break the plastic posts which act as "nuts" or bosses for the screws. You should be able to gently rotate them (Phillips head) while allowing for them to naturally came out (I mean: don't press down!).

There should be many assembly-disassembly information for HP-41C in the Internet, take enough time to read before beginning. Yours should be the variant usually known as "fullnut", in case you see the term. All 41C are "Coconuts", but later models have a smaller circuit board inside, and are called "halfnuts".

Good luck! Keep trying to revive this jewel which, in your case, will have an additional value for your son, as something passed from one generation to the next.

In case you decide not to open by yourself, there are some respectable repair shops, and you will find useful information in this site and in this Forum. Welcome!!

I'd like to underscore the caution expressed by the other guys.

If you decide to open it, be gentle.

If your son is going to open it, remind him that it requires *much* *much* more delicacy than putting a new graphics card in his PC. It will live again and give him years of service but *only* if it is treated with the respect that its 20+ years deserve. :-)


Thanks so much everyone for your ideas!I'll pass them on to my son when he is home on the weekend.Forgive the obvious,but should he clean the contacts and other parts you have mentioned with just plain alcohol or should I buy something else?Thanks again!

There are many really good help discussions on the 41 that have been posted here over the years---including some that Luiz posted for me over a year ago. Lots of details and imortant pitfalls, methods etc----go to "Archive" and then pick one (try at least the last three) and then search on:

hp 41
hp 41c
Vieira ("posted by")
platt ("posted by")

Note that the fullnut and halfnut are really different inside--and require different repair tactics.

Best regards,



Bill Platt

There is a very good article at:

Soldering wires as described might be too radical, but instructions for repairing the posts are very good.


The serial number starts with 2134S ... do you know off-hand if that makes it full-nut or half-nut? Thanks again.I will check out the archives as you suggested.

Hi Joanne,

take a look at this:


and scroll down to "HP-41C variations"

You will see a description of the physical differences.



Edited: 26 May 2004, 12:30 p.m.

I use 91% or stronger isopropyl (rubbing) alcohol. Best to keep it off the display window. It will leave a white stain (that can be polished off).

Hi Bill,
I have just spent the past couple of hours reading through the archives.Wow!There are some really great guys out there!I saw 'my question' asked a couple of times and have kept all the different answers for my son to go through.Probably should have read through them first before just jumping in.Thanks again.Will keep you posted on progress (or possible lack of ...)
Best wishes,

Since the battery contacts were clean, and she didn't mention any other problems (loose pieces rattling inside), I can't understand why someone would want to take apart a perfectly sound 41 without first trying multiple Resets first.

FWIW, in my case, if any of my 41's didn't power-up after changing the batteries, a few Resets always did the trick. Please let us know what fixes it. Thx.


Firstly, please first disregard my multiple use of "first", in my first response.


Hi Joanne

From the serial number I would guess that you have a fullnut (if the lcd display has square corners rather than rounded corners it's a fullnut) - the first two digits (22) give the year of production when added to 1960 - 1982 in your case which will be a fullnut (the earliest halfnut according to the museum is 1985) - the fullnut on my desk at the moment is also a 1982 (serial 2222S..).

Forgive me suggesting the obvious, but have you tried taking the batteries in and out for a few times - I've found that this will sometimes wake a 41 that has been sleeping for a while?

See also Resetting an HP41 which lists some ways of resetting a 41.

Occam's razor may apply here! My 41c almost invariably appears dead if unused for long periods.Stretching the springs in the battery compartment never fails to bring it back to life.I think the small batteries and their correspondingly small terminals need all the help they can to make a good contact.

Edited: 27 May 2004, 10:27 a.m.

Hi Joanne,

Probably should have read through them first before just jumping in.

well, that might be the general rule in usenet, but here, we just eat up anything that has to do with fixing an old HP-41C! (BTW my 41CV still is not fixed, but someday I am going to try again--you probably saw my pleas for help--and Luis' et al responses!).

Do let us know how the progress goes--we all live vicariously through the successful repairs of others (especially those of us who still haven't fixed the broken ones...)

Best regards,


Hello Bill, all;

first of all, thank you for your kind words and remindings. It's been -and will always be- my pleasure to be around and helpping the way I can. I take these words of your as the best rewarding, Bill.


Luiz (Brazil)