Help my 41C


I recently picked up a cherry-looking 41C w/card reader and three modules. Sadly, the calc itself seems dead. Well, let me put it another way. When I first got it, I hauled out the old AC adapter and hooked it up to the 41C's little AC-connection dots. Saw a flicker of life, a few words about Memory Loss, and then a blank screen. Uh-oh. So, then I went and bought the 4N batteries, and now I get nada. Did I mess up the machine? Anyone have any thoughts? Thanks, Erik


Ugh, the HP-41C doesn't have an AC connector, not unless you have a rechargeable battery pack in it. What, exactly, did you connect your adapter to, and what kind of an adapter was it?



Uh-oh. Well, on the right side of my 41C, next to where the battery pack slots in, there's a little hole with two metallic bumps. I just assumed that was where you plugged in an adapter. So, I took my junky all-purpose adapter, set it on 6V, and touched one lead to each of the metal dots. Like I said, I saw the flicker. Then I saw nothing.

BTW, this calculator is so clean in looks that I can't believe it's dead. The on/off switch is the on/user toggle at the top just beneath the LCD screen, right? Lord, I hope I haven't slain the thing.

Thanks for any help you can give.



The correct adapter *for the rechargeable pack* is 8VAC.

I don't know if the specs for the "buttons" are the same. Earlier HPs had a warning in the manual that they shouldn't be run without batteries in place. I wonder if HP redesigned the 41C charging system to enforce this.

HP was known to remove the buttons from early 41Cs sent in for service. Some people thought they were recovering the microgram of gold, but perhaps they were ensuring that no one did what you did.


Dave: Hmmm. All this being the case, do you know where on the battery buttons I might hook up an 8V adapter to see if I can get the thing up and running? (And why do you suppose it's 8V, given that the batteries are 4x1.5V?) Or do you think maybe I ought to sit tight for a bit and try not to do any more damage. Thanks, Erik



Don't connect 8V to the battery terminals inside the battery bay, you could connect 6V DC (to the outer two terminals, but get the polarity right !!), but better to use batteries. The 8V Dave mentioned is 8V AC used for the rechargeable battery pack, the charger plug doesn't connect to the terminals you tried but instead goes further through the "tunnel" to the terminals on the rechargeable battery pack itself. If you've bought 4 new N cells and it still doesn't work, clean the battery terminals, if it still doesn't work you've probably fried it. - John



on four HP C's; some C, come CV, some CX; I find that all will give "false OFF" indication if the key contacts are dirty.


spray CRC QD Electronic Contact cleaner into the front of the keyboard especially on all four sides of the ON/OFF key;

you might surprised that the machine was in working order all along, but that the ON key did not work!!!!

after spraying it, then toggle the key numerous times -

if that does't work use the Reset procedure outlined on page 385 of Vol II of the Manual.

Again, you might be surprised that the old machine will come to life.

Good luck!


I failed to mention that it appears that there is a capacitor in the 41 such that when fully discharged takes charging to reactivate. what this means is that sometimes, putting a fresh pack of batteries in will NOT instantly bring the machine back to life;


insert and remove the fresh battery pack a number of times while toggling the ON and USER switch;

more likely than not, at some point the display will activate, usually "Memory Lost", and the machine is back among the living.

I don't know the power design or circuitry of the machine, but what I've described works, and seems to be a reasonable explanation based on messing with them since 1984.

it appears that it is the act of repeatedly energizing and removing power to the capacitor that finally brings the machine to life; sometimes, even, when it has come back to life after a long sleep, it will go dead again soon, so one has to try the repeated energizing and removing power until the machine finally stays awake.

if nothing else works, send it to me and I'll be happy to see what I can do


Ah, so one of those old machines (I never had one of those) that had that extra adapter plug.

The problem is that most all-purpose adapters, when set to 6V, actually have a much higher idle voltage (up to 15V). It drops to around 6V at the nominal load, say, 500 mA. Since the HP-41C has very little power consumption, chances are that it got the full idle voltage of the adapter, and it got fried in a split second.



It sounds like he hooked up the connections found on early 41Cs that were never used. (Because the rechargeable pack, once released, had it's own connection.)

I have no idea what happens if you apply power there. I'm also not sure how he made contact between a proper 41C charger and those little "buttons", making me wonder if he was using the right charger.


Yes, it was possible to power the HP41 by providing a source of 6VDC to the "gold bumps".

This is mentioned in several of the earlier PPC issues. But the solutions seemed to revolve around 6V batteries rather than power supplies.

I concur with the argument about power supplies and high voltage without load.




The two gold balls are for a power adapter that HP never sold. They connect directly to the DC power buss inside the calculator. The 8 VAC output charger is for use with the rechargeable battery pack. After HP started selling the rechargeable battery packs they decided that there was no use for the DC power supply so they never released it for sale. They also quit putting the gold balls in the 41s. Only the 41s made in the first couple of years of production have them. Furthermore, since they severed no purpose, HP usually removed them from 41s that were returned for repairs.

I hope you didn't reverse the connections, if you did then you almost certainly fried the 41. If you didn't reverse them then it SHOULD be ok except for the original problem. I work on the 41s. Contact me directly if you want me to take a look at it.



One should know that cheap AC-adapters never give the right current. Next to that fact an adapter will not give a "clean" DC-current as a battery does. It will still have a 50Hz signature, basic electronic knowledge: how to transform AC to DC.

Erik, you should try to use the AC-adapter for your Pentium-motherboard, see what happens.......

For a very stable DC-current I allways use an old power-supply of a IBM-AT



Gawd, I'm feeling worse and worse about this. I mean, could I have really killed my 41? Okay, so it doesn't work on N's; perhaps there's something wrong with the battery box or with other simple connections. Is there no way to test for this? I am sooo very ashamed. Sigh.


Don't feel bad yet.

Post the serial number and we'll tell you if it's early enough to have all the bugs.

If it is, then you can feel _really_ sad :-(

What's the current value for a 41 with all the bugs?


the penalty for killing a 41 is that you have to use and program a 49 until hp makes something at least as good as the 42 again (there will never be another 41). i'm sorry, the law givs me no alternative. but if it will make you feel any better; i did the same thing to a 22 once :-(


Okay, at the risk a further humiliation, here's the numbers:


Do you suppose when I fried the calc (assuming I did indeed fry it), I also fried the other stuff hooked up to it -- the card reader and the modules Math I, Home Mgt, and Quad Memory?

I am feeling worser and worser ...


Hmmm 2452.... My reference lists that as being well into the production era of the HP-41CV. But you said it had the gold balls.

I was under the impression that the gold balls were removed before the CV came along.

I was expecting a serial number like 1950A...

Perhaps this calculator was sent back for repair, or was fixed by somebody who mixed and matched to get a working unit.

Does it have the upright keys or the more sloping keys? (you really need another HP41 to compare it with).

you may well have damaged the other modules. It depends on exactly how well you fried the HP41 :-(


2452S.... definitely this is not an "allbugs" 41C... Do the older 41 have a special value?


Well, if a bog standard 41CV is worth $US250 then an early edition 41C with all bugs should be worth several thousand on rarity alone.

Anyone want to but a 41C with all bugs for the bargain basement price of $US1750?

I thought not.


A lot depends on what the "old AC adapter" was. If it was the 8259 adapter for the 41's battery, then you ought to know that that adapter puts out 8V AC - the rectifier circuit is in the battery itself - and if that's the case, I think you'll find you've fried the calc.

If it was a DC output adapter AND if the polarity was right (50/50 proposition) you may be OK.


--- Les []


We used to be able to send them to HP,but Ive heard they don't repair 41's anymore. We use them for surveying and we beat em up pretty good. Any help would be apprieciated.

Forum Jump: