Dead HP11C


My HP11C is no longer working. The spring battery contacts no longer make contact with the battery. Does anyone know where I can buy replacements? I can repair the calculator myself if I can find the parts.



Just to identify what type of internals your HP11C has: when you mention that the spring contacts no longer make contact with the batteries, you see one metal strip on each side of the batteries compartment or one spring in one side (closer to the corner) and one small tab in the other? Would you describe them?

There are two basic internals for the HP11C (all voyagers, except the HP12C that has 4 different internals). In the HP11C you can identify the internals by the type of batteries contacts: if two metal strips, earlier type; if one spring and a tab, newer one.

Chances are that you may have a bad contact because of oxidation OR twisted strips. If you have to, will you open the calculator for checking AND soldering, in a worst situation?

Success! (and excuse-me for any failure in my foreign English...)


Hi Vieira,
Now I'm really confused. I have contacts that are link leaf springs. Each end has 3 pieces of metal. On one end, I see 2 are like springs, one is flat. Maybe they should all be springy, but the inner one is closer to flat. On the other end, I managed to break off (ouch!) the inner spring. The two remaining contacts look flat. I think they are supposed to be springs. I did manage to get my calculator to work again by putting a piece of copper shim in between the batter contact and the battery. This extra material did the trick. I still would like to find a supplier of those leaf spring batter contacts, but I now understand that the design was changed so it might be impossible. At least that seems to be the only problem with my calculator.


Great news!

And you are right. The mid metal piece of each contact (one for each battery pole) is there to keep the set firmly locked in the plastic sides of the batteries compartment, it has structural assignment, not electrical action. The two sided metal pieces are the ones to make contact with the batteries.

Your solution is a good one, and the best to be done by now is keeping like this until we find a better solution. The problem is that the copper may oxide, and corrode the contacts. I'd try to manage the remaining two metal contacts and remove the extra copper shim. I cannot think about how will you get a replacement except in other earlier Voyager. Anyway, I believe anyone that deals with metal springs in your town will be able to rework the remaining spring based on the other one in the opposed pole (they are identical).

If your HP11C is back to life, these springs are no longer the worst problem.

I'm glad your 11C is working. Please, post again if you need more advice.

Best regards.


Hi Luiz,

do you remember our discussion about a dead HP11C
the other day ?

Here is the good news.......he is alive again !!!

And this is the story: I bought a HP71B and read
about the ON/OFF-section...and maybe here I have found
the key...."8. If the display remains blank when "ON" is pressed...d. Press or hold down "ON" for about 30 seconds to *discharge the circuits*"

I pressed the "ON"-key about 60 seconds and now my
good old HP11C is working like a devil :))

Thank you, *OLD* HP, for the quality of your calculators.

greetings from a happy.........Erich N.


Hi, Erich;

this is the sort of news that amuses me. Thank you twice: addressing me and letting us all know about this new trick.

Taking a ride in your post: I started a thread a few days ago about "resurrecting" an HP15C by using an old HP11C's case and PCB. I was waiting for the chance to tell everybody that the HP11C is working... Yes, after disassembling it and removing the PCB from the case, I inspected it and saw a corroded and interrupted track. After cleaning and using a conductive ink, the HP11C's circuitry got back to life.

I did not give up the HP15C (forgive-me you who prefer the HP11C, but the HP15C is a lot more powerful), mostly because I am an electrical engineer and the HP15C works with complex numbers, matrices, integrals and has more than double available user memory. As soon as I am definitely decided to do it, I'm removing the 11C's IC's and testing the 15C's IC's. If the HP15C proves being alive, I'll keep the 11C's IC's as spares. I'll let you know.

For your HP11C, Erich: Live long and prosper!



Hi Luiz,

I wrote it to you ( and the others ), because I know
that we are loving these positive messages.

But I wouldn't belong to this "mad" community if I would
only working with a HP11C. Here is another story about
one of your favorites....a HP15C. [ the Voyagers are the sexiest of the HP's to me. Pioneers probably the best in daily using, performance and the huge number of functions.
But 41C is all-time-winner]

I bought this HP15C with a known flaw: the lowest segment
of the rightmost digit didn't work. When I tested
the machine the lower segment of the fifth digit additionally wasn't working. But when I hardly pressed the metal surface of the machine it works again....sometimes. Hmm, seems not to be a very serious problem. Because I had this victory with my HP11C yesterday, I tried the same procedure ( remove batteries and press "ON" 30-60 seconds ) with the HP15C. Ooops, now the first flaw ( defective lower segement of the very important rightmost digit ) was gone, but the other one is still there :((

I'm full with hope that I will find the cause of this minor defects and to give this marvellous machine a greatful future.

thanks for your encouragements.......Erich N.


Hi, Erich;

just for us to be sure about which internals does your 15C have.

Look at the batteries contacts and verify if there are two metal strips, three slices each, or one spring in the positive pole (leftmost) and a small, golden plated tab in the negative pole. If option one is true, you have a flex-circuit assy 15C; if option two is the one (spring + tab), yours is a single PCB model.

Ahead with the difficulties on disassembling, I prefer option two, mostly because circuit stability is better, and repairement is easier. If you need so, I have both types as disassembled stuff, so I can generate some images (no photo camera, just an acceptable scanner) for you to think about it.

Let me know if you want to.

Success. (I also have the Voyagers as "perfect" in many aspects. It seems as if they were designed with pashion. I feel "excited" when using them, and about being sexy... I just did not give my thoughts this sort of freedom of speech. But I agree with you...)

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