Shockingly new HP41CX !


I just bought a brand new beauty, a mint-mint-mint HP41CX. However, the seller put 4 new 12-volt batteries into it before he mailed it. With 48 volts instead of the correct N-cell 6 volts, the little guy took quite a shock! Anyone got any idea what would have happened inside the innocent calculator (halfnut series) and if it can be un-cooked and revived?


I would start by not touching anything and getting my money back!


Godon: Thanks, and I did do that. The seller agreed that he was pretty much a full nut for over-zapping the half nut. We re-negotiated so that I wound up buying at a "salvage" rate rather than a "new" rate, quite a savings, but for what? Probably now I have a very nice looking piece of junk. But if anyone still has any ideas ...


Now look for a beaten up halfnut which still works and swop out the electronics....


Swapping out the guts of a halfnut is not a very satisfying experience... heat stakes a mundo... never will feel quite the same again.


Spread a little cream cheese on it... it's toast.


We need a place for horror stories like this.

I have some inexpensive multimeters that use that 12V battery. I expected it to be hard to replace but then I was surprised how available and cheap it is. It never occurred to me that it was easier to find than N cells!

What a tragedy.

I wonder if there is any chance an electrolytic cap might have shorted out and protected the ICs?


If you want a place to post horror stories, start by posting it here. Be the first.

HP Calculator Horror Stories


I don't know if my 12C that I found in the street is a horror story or a success story, but I'll definitely post a description of my HP67 that had been attacked with a screwdriver.


This might be silly - but you didn't say if you have tried the correct batteries in it yet.
Who knows!!!! Maybe there is a guardian angel for HP41CX's.


For those of us that weep about the pain this nice machine suffered, at least know that I did not lose financially. The X-memory and Advantage modules inside survived, and I could recover all my costs and still have a nice looking dead, dead, dead 41CX to look at (oh, the humanity ... oh, the insanity ... oh, the inhumanity). Funny how we think of these things as living, or in my case as once-living. I'd like to thank those who have responded and for those that still might. I posted this on a more obscure site yesterday and someone emailed me with a cryptic: "post it at the HP museum forum, and you WILL get answers." I think he knew what type of sad answers I was going to get. Anybody think the Smithsonian would trade me with the one they have that Sally Ride rode in space with? That one doesn't have to work any more, so mine could sit in just fine, right? Just joking ... thought I had to say that, because there may be people here even more fanatical about the old HPs than me (or us).


some of the individual chips ma still be avive, or maybe the lcd. the keyboard and case are fine, and the battery holder is probably good.

Which could end up meaning a lot if used as a parts machine.


that was me that wrote you about your post at the other website. i did forsee some sad answers but since i don't know squat about electronics i didn't say anything. christof is probably right that there are good leftovers. you can keep an eye out for a physically distroyed 41 with a good pcb. surveyors are forever ruining 41s by pounding on the keys till they are flat or droping them or (ouch) closing them in the truck tailgate. the ones that just die of terminal dirtiness go easy. hey! maybe i should post the tailgate story on mikes horror story site.


how do you know that it doesn't work any more? did you check it with the correct batteries?
if not, then you might give it a try. although 48v are definitely destructive for the calc, i know from own (in other(!) circumstances) experience, that these 12v cells are pretty high ohmic. so, if your 41cx has an overvoltage protection on board, maybe that protection clipped the battery voltage down to a save level?? just a guess.

cheers, hans


I agree with Hans - give it a try with the PROPER batteries.

I once (inadvertantly, of course!) connected a Sony tape voice recorder (the kind that use mini-cassettes) to a power supply wall wart that has selectable output voltage. (You can use one supply to power all sorts of equipment - it has about 10 different kinds/sizes/genders of plugs on the end of the cord.) I had the voltage set way too high - probably 12V versus the desired 3V. Smoke actually came out of the tape recorder! After a few moments of "Oh s**t! What have I done," I plugged it back in with the correct voltage selected, and it worked fine. It's still OK after many more years.

So, give it a whirl with the correct juice.


I've been an HP-41'er since back in ol' '79 (and a '35er since ol' '72). My how time modules fly. So, sure I tried the right batteries ... and a Vulcan mind meld ... nothing. It's so perfect I have not had the heart yet to take off the rubber feet and unscrew it to look for any smoking parts. Having another 41CX halfnut that I have to open and clean often, it does not look to me that there is an easy-to-get-to pcb fuse, etc. I looked at the block diagrams in the repair manual posted and was not encouraged. Someone very smart about these units offered to have a look, and I think I will send it over before I do anything to it at all. I told some people at the office (who observed I was in a sad state) that it was like plugging their car radio into a 120-volt household outlet, but that would be a 10-X overvoltage and my calculator ONLY got a 8-X spike. Plus, to make my analogy more fair I would have to rectify the AC household current too. And, even if those 12-volt batteries are "ohmic" it doesn't seem like it would take much current to make things unhappy at 48 volts even for a mini microsecond. Of course, I was hoping for a miracle, something like: "This is no problem really. Just take it apart carefully and replace the big capacitor in the lower left that you will notice has had its top blown off. Buy one at Radio Shack and carefully solder it in." But I don't think a miracle cure is out there. Again, thanks to all those who have commented on the sad fate of a never-used HP41CX.


By the way, you are not alone... I know of at least two other HP41's that bit the big one the same way. If it was a fullnut, it would be repairable (or possibly even OK). The power converter in the halfnut is located in the main chip... and it does not like all them volts.

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