buttons on HP-25



I've recently uncovered my HP-25 from the attic, where it's been since undergrad days. Rebuilt the battery pack, and everything seems to be perfect, except for a couple of keys. The "4" and "2" key have the same tactile feel as the other keys, but I have to REALLY PRESS HARD ;) on the keys for them to close the circuit. I took the calculator apart and cleaned the exposed circuit board with contact cleaner, but it didn't help. I'm afraid to try and separate the circuit board from the keyboard - it looks like they're molded together.

Any suggestions?





please, check if there is a small, golden-coated hole in the printed circuit board under the very middle of each key. There is a type of keyboard assy that does not have these holes; if yours have, you may clean the contact.

As you do it, I'll try to find the thread where the cleanning procedure is detailed. Anyway, if you want to try, use a brush with long, thick bristles. You can even separate a couple of them as a bundle, soak them with the contact cleanner, and gently insert them in the mentioned holes. Move the blisters in and out, rotate them, remove them and try again.

If the keyboard's PCB does not have holes, it seems your keyboard is the one with plastic bubbles under each key. This assy has copper trails in the inner side of the bubbles, and these copper trails tend to crack. I am trying to find a better solution for this kind of problem. It seems that self-adherent cooper foil is a possible solution, but fixing it in a permanent, steady state is another issue.

I know it does not help that much, but maybe you can use this info as a guidance for your own skills.


Luiz C. Vieira - Brazil


I have the same problem with my HP45. I also had the same problem with my HP32SII and solved it by washing it in water several times.
Does anybody know if I can try this proceedure with the HP45? I am a bit worried about the different display.
Thank you.



some HP calculators, like all Spices (series 30), Topcats (HP9X), Woodstocks (series 20) and Stings (HP29C and HP19C) have a particular LED's display assy: it may be opened. Classic models, HP45 included, have a sealed LED assy, in general it's a set of three five-digits packs. Your HP45 has this sort of sealed assy, and the HP32SII has a sealed LCD display.

One should not wash units from the series mentioned above without removing (when possible) their displays.

About keyboard bad contacts: there are some different approaches for cleaning, mostly when the cause is already known. I do not wash the keyboard PCB unless it's necessary, otherwise I prefer cleaning by other means.

Using water is not harmfull, but it must be free of dissolved ions (neutral PH, if possible). I am not sure if distilled water is better or worst, I would like to read from the others.

What do you think, guys?

Best regards.

Luzi C. Vieira - Brazil


The 45 can be completely disassembled, you can wash the keys and clean the keyboard switches. The Classics have flat strips with a bow in them rather than a dome for the bistable mechanism and I have read that they would break more often than the domes, but since they can be completely disassembled, it might be possible to replace the strips if they break.


Hi, Ellis;

you're right. I did not make a correct reference (that's what happens when you're almost tired-out and writing...). The correct sentence should be:

One should not wash units from the series mentioned above that have the LED assy that can be opened without removing (when possible) their displays.

Thank you for posting a correction.


Luiz C. Vieira - Brazil

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