Hi, professional answer, if a fuse blows it has done so because it succeeded in it design function, and not because it wanted to hack you off. on rare occassions fuses may fail due to age and stress but that needs to be a decision arrived at by a qualified service tech. Microwaves operate at some 4000 VDC and can under fault conditions kill even when unplugged for quite some lenght of time. Most likely cause of failure, faulty interlock switches, followed by the high voltage components. See my answers elsewhere under this heading
kindest regards
B.E.S. Microwaves
01424 447799
patrick
March 2009