dead keybaord after minor surgery

[Castellen]

@punk_guy: :-P

@ivansc:
Yep, that's a fairly common problem.  I agree with KennyR that the keyboard microcontroller (the mask programmed HC705 beside the ribbon cable socket) should be fine.

When plugging in/removing the keyboard a few times, the conductive pads on the end of the ribbon cable get small holes scratched in them, and the connector pin no longer makes reliable contact.
Sometimes if you pull the ribbon about 1mm up from the bottom of the connector BEFORE pushing down the retaining clip it'll work good again.

Otherwise you can look carefully and see where the damage is, then trim a little off the end, so that the holes are below the connector's pins.

[Castellen]

The A500 keyboard is a bit different to the A600/1200 as it's connected by serial data in the same fashion as the big box Amigas.

Take the keyboard apart and find the PCB track (row) which is common to the faulty keys and use a multimeter to check the track continuity from each keypad to the input pin of the keyboard microcontroller.
Chances are there could be a broken track, or dirt/grime on it somewhere causing the row to be held permanently active.