Amp blowing right channel fuse?


I have a friend whose HK pm665vxi is blowing fuses for the right channel. I've never blown a fuse. What could cause that and would the cause have to be internal? Why would it blow a fuse rather than go into protect mode?
arnettpartners
The first question would be: is this a line fuse, or a B+/B- rail fuse, or a speaker fuse?