HELP! B-52 LG-100A Blowing fuses!

[JackRobot]

Hey guys,
A friend let me use his b-52 LG-100A amp head, and being my luck, I was playing it, low volume and it blew a fuse, I put a new one in, and it blew it again, I took it apart and didn't seem to see anything burnt, it never seemed to get hotter then normal temp, the only thing I saw, was where the rear circuit board connects to the aluminum in the back, there are 3 small hard metal connectors that go into it. And the metal around them seems to have melted away? Thats the only thing I could see? Any help would be great,  I really need to get this fixed, I know a shop will cost me an arm and a leg, If anything i'll just buy him another one as you can find them for around 150 bucks on e-bay, Should have just waited and not used someone else's stuff  :grr

Thanks!
Jack