Hello
I'm looking for some leads on troubleshooting a Mac 128 keyboard. So far I have ruled out any issue with the Macintosh and that other keyboards work fine with it. I have also ruled out the cable as other keyboards work fine with it. I've also tested the logic chip and confirmed that the ROM on the board are both fine. I replaced the capacitor. I think it's a 63 Volt. I've also tested the key switches to confirm that they make continuity when pressed at this point. I'm kind of out of ideas. I can't find a schematic for the keyboard either. Anyone else have any ideas on what to check? I thought maybe there would be a Crystal on the keyboard however I'm not seeing one any help in next steps for troubleshooting would be appreciated
by the way, I've also confirmed that 5 V and ground on the board itself are being delivered
It sounds as if the logical next step is to use an oscilloscope, or at least a logic probe, to check if the pins of the microcontroller are doing their expected thing. The chip is connected (or should be) to the rows and columns of the key matrix, and it scans them continually. So you should see pulsing on the row outputs.