I have had to change the fuse in a handful of my microwaves,usually when they get to be about 10 years old.If you take the housing off,you should find an inline fuse holder on the power cord just as it enters the housing.Read the info on the fuse,and replace it with the same size/type(the ones I've seen are ceramic fast acting fuses)I also like to take another spare and tape it inside the housing near the fuse holder so I don't lose the spare.