Pre Amp Fuse Blowing

I have an old BK CS115 that has been working fine.

Last night the fuse blew, now every fuse I use go's the same route.

check all external wiring.....any ideas?
I have owned a preamp that did the same thing and it was determined to have a bad transformer. But there could be other possible problems with yours. Take it to a tech and get an estimate on repairs to determine if this preamp is worth repairing, mine wasn't.