HP-25 Co-luminous segments

[Tom Flatterhand]

Ok, I dared to do it. I got the rubbers out in one piece. Using a multimeter with continuity check, I identified the fourth contact from the top right of the keyboard as the one connected to the row of keys. This leads into the board where the LED unit is plugged in. I have marked the corresponding line in red in the picture. It seems to run a hair's breadth past the two contacts of the power supply and then to IC 1280-1382J 51147.

I plugged and unplugged all plug-in units several times, wiggled a bit everywhere, but nothing prevented that the upper segments did not turn on when pressing the buttons of the middle row.