I would say it is possibly a fault in the power supply, maybe a rectifier. Unless you have some basic knowledge of electronics, a multimeter for testing, and a soldering iron for replacing components, there is nothing much you can do.
I repair amps and live in Aberdeen, if you live near there contact me.
enqiries@amp-repair.co.uk
Robert Hossack
June 2008
If the fuse blows immediately upon insertion, you most likely have a short somewhere further down the line. It will probably end up being cheaper to replace it rather than repair it.