Post #3658343
2026-07-07 21:34 UTC
This is the excerpt from the keyboard schematic with the non working keys highlighted. It's a standard keyboard matrix implementation, the 74LS138 decoder pulls the output Y0...Y7 that corresponds to the binary number at the inputs A, B, C (pins 1-3, repeatedly counting from 0-7) to a logical 0 level. A pressed key connects the output connected to it to one of the inputs on the left (two per key for touch sensitivity), so the keyboard controller can figure out which keys are pressed.
Replies (2)
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@me_@sueden.social 2026-07-08 17:44
Now I know where all the dirt and rust was hiding… removing all 88 keys took a while!
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@me_@sueden.social 2026-07-20 21:15
Found the problem... the metal base the key PCB and mechanics are mounted on showed significant corrosion and the PCB itself also suffered from this. The highlighted trace is broken, this is the connection shown in red in the schematic.