Anyone know what might be wrong with my ampeg svt 350? It quit on me at last night's gig. Worked fine for the first few minutes of soundcheck. I turned it off to switch cords, and then back on, but nothing. No sound at all, no lights, nothing. Bass was working fine. Tried new power cord, different outlet, replaced the fuse, but nothing worked. I ended up going direct through the PA. Before I bring it in for repair I'd like to have some idea of what might be wrong with is so I don't get ripped off. Any ideas? Thanks!