My original HP-25, ailing

[Peter Klein]

I took my original vintage 1977 HP-25 out of storage and tried it out. The last time I used it, the calculator worked fine, but the memory (storage registers and program steps) did not. A couple of number keys were intermittent. This time, the calculator would sometimes display the opening "0.00", and I could enter a few digits, but then the display would start to go crazy, as if each LED digit was rapidly vibrating on and off at random, and/or baubling on and off one after another from left to right. And eventually the display would go completely dark, and stay that way until I disconnected battery and reconnected the battery pack (running off two Emloops NiMH AA batteries). I also tried a 3v power supply, same symptoms.

I'm torn. I could buy a Panamatik kit for $95 U.S. and attempt to fix it. Or I could sell it off for parts and move on. It would be nice to revive the calculator that started me on my HP journey. But I'm not sure if I want to sink time and money into a 46 year-old calculator, considering that I have a bunch of more advanced models that work well, and that I think either a DM32 or DM42 is in my future.

I have an oscilloscope, so I can measure the timing signals as suggested in the Panamatik manual. If I decide on fixing it, I can run that test before I commit to the kit.

Could someone point me to an article or post that explains how to clean the keyboard buttons? And how to remove the rubber feet that conceal the fastening screws without damaging the feet?