I've got a problem with my Amiga 500.
I swapped the CIA 8520 chips, but the problem does not change. Any ideas?
Despite some strange popular belief, the CIAs have no involvement with joystick/mouse movement. In the A500, the 4 movement lines are read by U4 (Denise). Reseating or replacing this socketed device may solve the problem for you.
The 8 to 4 line multiplexing (to read the four lines from the joystick movement and 4 lines from mouse movement) is switched by U15, a 74HC/LS157. Replacing this might solve the problems as it may have been damaged. I think it's soldered in as opposed to being socketed. The multiplexer is under control of a system clock which is generated by U2 (Gary), so reseating this device may fix it as well.
With a bit of luck it might just be yet another problem caused by IC sockets.
