I'm not familiar with Crate specifically but here are some general answers.
Blowing fuses is generally caused by a short-circuit somewhere. If you know where in the circuit the fuses are located, it may be possible to narrow down the range of possible faults, but without knowing that, all I can tell you is the common areas.
The output stage is the commonest fault area. The output devices (MOSFETs or transistors) are the big devices mounted against the heatsink. Often the fault is caused by a mains voltage surge. Usually the output devices and many other smaller devices are destroyed (there may be visible signs like cracked components, but not necessarily). In this case it's often not reasonable to replace the damaged components, especially if exact replacements aren't available locally.
Other common fault areas are the mains transformer and the bridge rectifier, and damage from external sources e.g. liquid spilling in through a vent or components getting pushed over and touching each other.
If you can email me a schematic diagram (send it to kris at heidenstrom dot gen dot nz) and tell me which fuses blow, I can give you a more specific answer and suggest some measurements you can make.
Kris in Wellington, New Zealand, December 2009
