Notice there's two fuses to the right of the big capacitors, if the power amps had blown, those fuses would blow rather than the mains fuse. The rectifiers are most likely, but failing that it's probably the transformer.
If you don't have a meter (and they are so cheap there's no excuse not to), then unsolder the four rectifiers, and see if it blows the fuse without the rectifiers. If it does, then it's most probably the transformer, if it doesn't, then stick the rectifiers in your pocket and take them to Uni with you, there's going to be big rooms there all full of meters and people who can work them!