It should be very simple...


I bought my HP-45 off of eBay for a cheapish price ($45, oddly enough...) because it showed wear and some of the buttons had to be pressed very hard in order to work. From the start, I suspected that the contacts were just dirty from 30 years of use. So I took 'er apart and thoroughlly cleaned the contacts. This was a bit of a trick, as the contacts themselves aren't readily accessible. I kind of very gently cleaned underneath the flexible metal strips that complete the circuit when a button is pressed with a toothbrush dipped in rubbing alcohol. I'm 95% sure this is your problem. Elsewhere on this site are instructions on how to clean this contact by preparing a small strip of 1000 grit sandpaper. Go back to the main page and look on the link bar to the right until you see the part about repairing HP calcs. If you poke around a bit, you will see what I'm saying.

The capacitor replacement would be overkill in this case. The reason they suggest replacing the caps is because sometimes electrolytic caps get fatigued over the years and eventually, they could leak and mess up the board. Personally, I wouldn't go this far unless I were having that problem or I suspected damaged cap. I think in your case, it is just a dirty contact. Figure out a way to clean that contact, and you will be golden.


PS - I don't know if you're the type of person to disassemble your calc, but once you have it apart, you will find that it is not such a big deal.


There is one cap in the reader circuit that is well known to have a particular failure problem that causes the reader to write but not read. The cap is the small blue dipped tantalum electrolytic capacitor on the card reader board. I replace them on every reader that I rebuild... I suspect that they will ALL fail eventually, just like the drive roller.

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