Ashdown ABM 900 blown fuse question

[fasttheo]

I have an ABM 900 that blew the rear power jack fuse over the weekend. I always use a surge protector, so I have eliminated the 'outside surge' theory. I opened the head, and one of the nuts that hold the lower bolts (the ones that connect the head to the wooden housing) was rolling around loose. Could this have caused a short that lead to the blown fuse? I removed the nut, put in a new fuse and everything powers up and plays fine. I plan on having my local guitar guy test fuses/wiring/etc with a meter, but I have a gig coming up and i'd rather not use the MAG backup head (although its a great, reliable head). My first reaction to a blown fuse is to assume the worst, but could it have just been a short? Sorry for the long (and probably dumb) question.