HP-25 Co-luminous segments

[teenix]

Luckily, I don't think corrosion is an issue. :-)

I know you can get funny displays by pressing multiple keys at the same time, but it is hard to imagine the keyboard having a hard short as it would show up other operational problems. The same for the display module.

This seems to point to a chip problem.

As mentioned, because the display/keyboard operate in a multiplexed manner, an oscilloscope would help diagnose the problem. A shame I don't live around the corner, I would be happy to have a look.

Careful handling the board, the IC's are sensitive to static discharge coming from you.

cheers

Tony