Keyboard doesn’t respond
Step-by-step diagnosis for the Amiga 500 rev 8A board. Each step lights up the signal or chip to measure in the explorer below.
The machine boots but the keys do nothing. Keys reach CIA-A over a serial data line and a clock line.
- _KBDATAShow on board →
Keyboard data
At rest the line sits high and pulses on every key. If it doesn’t pulse, the fault is in the keyboard or the path to the CIA; if it does, look at the CIA.
- _INT2Show on board →
CIA-A's interrupt
On the eighth bit of each key, CIA-A pulls _INT2 low to tell the processor. If data and clock arrive and _INT2 never moves, the CIA received but did not report: suspect it.
- U7 · 8520 CIAShow on board →
The CIAs
CIA-A receives the keyboard; CIA-B handles the floppy. If they are socketed, swap them: if the fault moves from the keyboard to the floppy, that CIA is bad.
Didn't fix it?
We repair these boards on our bench in Loures. The request already includes the board and the fault.
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