2275-65 EX blowing a fuse

My MusicMan 112 sixty-five (2275-65 EX) went silent suddenly. I opened it and noticed the 2 AT fuse was blown. Replaced it and tried again. Blows everytime I switch the stand-by on. Same result with or without power tubes. Any ideas? Typical faults that could be causing this?

Aarni, does this amp have the 12AX7 phase splitter tube? It sounds like this is the Scandinavian version with the 3 secondary fuses. Is this correct?
If the fuse blows when you switch on the Standby switch, it could be the diodes in the high voltage supply (D9 and D10 in the solid state phase splitter version). Another culprit could be a short in either a plate 'snubber' cap or the protection diodes connected to the EL-34 plates.
FWIW, that is the *only* issue I have ever had with my own 112 Sixty Five - a shorted plate snubber cap. Of course it had to happen during a gig.
-Lars Verholtwww.captain-foldback.com

Thanks for your reply! Helped me a lot. There was indeed a shorted cap connected to the plate. Replaced it and works fine now.
Not that it matters anymore, but yes, it's the version with three secondary fuses. No 12AX7 on this one.