First, locate the microwave fuse, which is usually an inch or two long and made of ceramic or glass. Once it is located, a microwave fuse can be replaced by removing the microwave's outer cabinet and putting a new fuse in place, according to Part Select.
According to Do It Yourself, a microwave oven is prone to short-circuiting caused by severe voltage fluctuations. The microwave fuse ensures that an electrical surge does not damage the inner components by using a special filler material to break the electrical circuit. When fuses get blown or melt, they can be replaced in a few simple steps.
First, remove the back plate with a screwdriver, and locate the fuse holder. If the fuse seems stuck, remove it from the fuse holder clips with pliers. Take note that a blown glass fuse develops a black appearance, while a ceramic fuse requires a voltmeter to determine whether it's blown.
Second, get a replacement fuse. It is better to take the blown fuse to an electrical supply store to get an exact replacement, especially when the fuse does not carry a voltage or amperage labeling.
Finally, once a replacement fuse is acquired, insert it in its dedicated slot in the fuse holder. Press the surrounding fuse clips together to secure the fuse. If the fuse does not seem to fit in its slot, clean the fuse holder and fuse slots using a dry cloth wrapped around the tip of a flat head screwdriver.