How can I tell if I've blown a fuse?

If you look at the fuse, the wire inside may be broken/discolored. If you are unsure, just find the exact type of fuse and replace it. I am far from an electrical guru, but that's what I would do if I'm unsure if it's blown.

You most likely would not have the fault indicator if the fuse was blown. I would start by disconnecting the input and speaker wires to see if it corrects the fault. Often times something external to the amp causes the protection to trip. A bad input or shorted speaker wire are the most common reasons and amp will go into protection. If you heard a "pop" one of the large filter capacitors may have vented, meaning the top opened and puked the cap's internals onto the circuit board. I believe the warranty is three years on the X2 and A1 electronics, if it's out of warranty any competent shop should be able to repair it.

Good Luck

Ron