There is a Fusible Resistor beside the Joystick ports on some A500 models, it is a light blue colour and can be blown easily if it's blown there is no power to Pin 7 of CN1 (Mouse/Joystick 1 connector). I think it's labeled R401. (That's Power to Pin 7 of the connector)
It was only on Later A500 motherboards not the earlier releases.
