Help with this HP-12C


I'm trying to fix one of my hp-12C that insists in display sort of an adolescent behavior, like some teen agers will.

It operates for some 50 seconds to 1,5 minutes, and calculations are ok in this period of time. Then it suddenly crashes, the display blanks and the hp-12C will not respond until I take the cells out and wait for some 30 or 40 minutes.

I've resoldered the contacts (spring and stand) that touch the button cells and rechecked everything from the visual point of view.

Can anyone give a piece of advice here ? Did you experience the same with your Voyagers ?

Thank you


BTW, it's amazing how few electronics is included in this calculator ! I could find only 2 CI and 2 discrete components. I didn't check under the isolated protection for the display element, but there is no space for many more ICs.


Oi, cara! (Hi, pal!)

It seems you have an old, good HP12C. The most recent ones have only one IC (even the mid-term ones, between the three-button cells and the single 3.3V cell). Yours is a lucky ancient.

I would solder, also, all of the IC's terminals. This procedure worked fine with one HP11C and a mid-term HP12C (the one I mentioned that has only one IC and keeps the three-button cells).

If you believe this is risky, you can try "conductive ink". As you are in São Paulo, you may find some sort of conductive ink at the dedicated electronic shops (Santa Efigênia, isn't it? I'm always confused with Rua Aurora; which of them is in São Paulo and which is in Rio de Janeiro?). If you find the ink (there are golden and silver ones, you pick), you should try "painting" each IC's terminals at the point they touch the printed circuit board. The only problem is that if it does not work, soldering them after this will "burn" the ink, leaving residual stuff that may cause future problems.

If you believe you need some more info, e-mail me. Let's talk about it.


(I owe you a telephone call... Forgive-me)


Hi, Luiz

Thanks for the suggestion. I´ll try this asap.

As for those streets, both of them are here in Sao Paulo. In fact they will cross in famous corner in our "electronics bazaar district".

(I called you yesterday, but ...)


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