HP-25 resurrection adventure – Part 1: The Keyboard

[metawops]

Well hello folks! I've been absent from the community quite a while now but (of course) never lost my passion for all things HP calcs. ;-)

I just stumbled upon the fantastic ACT replacement hardware by Bernhard Emese (PANAMATIK) for the HP-25 (and others). This made me take my good old HP-25 out of the display cabinet and check it out.

Turns out: the obvious. Corrosion, leakage, the usual. After cleaning with IPA everything, including the keyboard, it seemed to work fine again. When turning it on it shows the well-known "0.00" at the left. Entering numbers works flawlessly now.

However, a strange thing is happening that renders the unit unusable: upon pressing almost any key (besides the numbers 0-9 but including the decimal point) or invoking any math function the display goes dark for about 0.5s and then shows "0.000000000".

There's one exception: setting the FIX, SCI or ENG modes works. So the f key works, too, obviously. I bet all the keys work fine but they're not doing what they should.

Is this a typical sign of a fried ACT?

I did all the measurements Bernhard suggests in his ACT manual – everything seems to look fine, even the frequencies measured at the pins 16, 17 and 20 of the ACT.

So what might be a next step here for me? Anything I can investigate further? Or am I already in for a new ACT from Bernhard? Any advice very welcome! :-)