it's all explaned in the TJ's Link :
2) On the later model Amiga 2000 systems this is usually due to a blown fuse, F1, on the A2000 motherboard, though the port controller chip is also a possibility; early A2000 revisions did not have the fuse, so the chip is definitely the source of failure. For other models, it may be a similar fuse if such exists, or the port controller chip. Static can blow the fuse or chip, but an attempt to use an incorrectly wired GPI cable on the joystick port is another common cause.
On those models with a fuse, the fuse must be replaced, and is a soldered-in component that looks like a resistor, but is green in color. The component is located right behind the mouse and joystick ports. You will most likely wish to have a service center do the repair.
Or maybe, a broken track...
