A customer recently shipped us an Amiga 600 that had no mouse movement. This was not a terribly difficult issue to resolve, but we had to check a few things as the board had a small amount of corrosion.
- Checked if the second joystick port worked, it did not.
- Verified the M0H and M0V traces were making there way from the far right side of the board to the Denise chip.
- Repeated the above with the M1V and M1V just in case.
At this point there was only one likely cause left, the 2:1 multiplexer; 74LS157. We went ahead and replaced this and success! We once again had mouse movement. We verified everything looked right in Amiga Tech Kit!