I have two different sources which have parts lists and schematics for the A500.
Neither of them indicate a R401, but they DO indicate an RP401 (probably RP = resistor pack) which is 4.7k x 9. The revision of the motherboard is REV 5, Rock Lobster.
They are pull-up resistors on pins 1-4 on each of the joystick ports.
Should be located top right of the motherboard.
I'd be willing to bet earlier rev motherboards had individual resistors instead of the resistor pack. The value should likely be the same.
I hope this helps.
kamiga
