I recommend replacing the fuse even if it looks good. It's going to be the cheapest solution. More than likely, there's also a fuse in the preamp. You should check that too.
Do you think it's likely the amp or the preamp?If it's not obvious where the problem exists, you'll have to do some basic troubleshooting. Can you pull out the amp and replace it with the one in your other system? If it's not the amp, switch out the preamp. That should help isolate the problem.