HP-25 resurection project

[Maximilian Hohmann]

Hello!

(12-01-2020 10:44 AM)wbvreeuwijk Wrote:  Doesn't look too bad, other than some green stuff on the tracks and it appears there are some components missing.

It really looks quite nice inside and out (compared to others I have seen) and there are no missing components. I happen to have an opened one right on my desk that I bought as defective from eBay last week (for 10 Euros). It seems to have some contact problems only because I could briefly see "0.00" in the display.

To get rid of the green corrosion you can (safely!) immerse the main PCB in a little bit of vinegar (not the keyboard or display though!). I use it pure because with diluted vinegar it takes much longer. Rinse it very well thereafter and let it dry completely, e.g. with a hairdryer.

I'm sure that you have already come across (many times...) the most important issue regarding these calculators: Never ever power them with anything but batteries or a regulated DC power supply set at 2,5V. Throw away the orinial charger otherwise somebody might plug it in ad fry your calculator... There is no polarity protection either, so mark the "+" and "-" connections clearly.

Good luck with bringing your HP-25 back to life!

Regards
Max