Keyboard doesn’t respond
Step-by-step diagnosis for the Amiga 4000 rev 2 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.
- _KBCLKShow on board →
Keyboard clock
KBCLK clocks each bit. Without it the CIA reads nothing, even if the data arrives.
- _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.
- U350 · 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.
- _KBRSTShow on board →
Keyboard reset
Ctrl-Amiga-Amiga pulls _KBRST low and restarts the machine. If the line sticks low, the machine won’t even boot.
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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