Texas TI-34 solar scientific calculator from 1987

[LEDfan]

@80sTI34
From the teardown this area is exactly where the zebra strip makes contact between the solar panel and the PCB. Zebra strips rely on a tight fit between component and PCB. If the tolerances aren’t quite right in your calculator, then pushing in this area might be making a connection, and powering the calculator.

If the calculator stays on for a few seconds after you have pressed down, sufficiently long enough for the capacitor to charge, then it is likely this that is causing the issue.

If you’re able to enter digits, and they reappear when you press down, then it might be a similar issue but with the connection to the liquid crystal display, as this would suggest that power is getting to the board.

Also in this area, there is the chip. This might have a poor connection to the board, perhaps a dry solder joint or mechanical damage from dropping.