My UMC 5200AAS keeps on blowing the internal ceramic fuse, about once a month. Any suggestions why it would be blowing the fuse? Otherwise it works fine, even when I replace the 20amp fuse.

Most MW do have an internal fuse, most likly a 10 amp ceramic (HRC) You can replace with a glass one but if it blows it could rupture

Maybe... Did you check the high voltage diode?... A shorted diode keeps the fuse blown... Ty

3 Months old? Under warranty surely. Just call Panasonic Repair Service for a free repair.

There are fuses in there but they don't fail for no reason.

your ceramic internal fuse blew, you can get them at most hardware stores its either a 15 or 20 amp ceramic fuse, then if this blows again chk your h.v. capacitor,h.v. diode,or the magnetron tube for defects

If there is no sign of power at all it may be that the fuse for the internal power supply has blown.

These are normally a special ceramic type and I have seen these simply give up when a microwave oven door is slammed shut a bit too hard. Recently happened to me.

The fuse should be visible as soon as you have removed the main casing. They are a special ceramic type. Normally if you look on the circuit board where they are mounted on you will see the rating for the correct fuse.

Try this first, If it fails again then something is drawing too much power and it should be further investigated by a service engineer.

Chances are if the varistor fails, it fails drastically causing a short circuit across the supply. It will sit across the supply (it will look like a thick ceramic capacitor) and you can check for continuity after isolating that at one end. If it shows low resistance (it should show almost open circuit with a Digital meter), replace it.

It need not be the culprit. If you are familiar working with High voltage circuits ( they are lethal inside a microwave ovens as the current capability is high here), you can discharge the doubler capacitor and isolate the high voltage diode to check for shorts in the HT area.

Replacing a fuse Locate your fuse. Most microwave fuses look like the one pictured to the left. They are usually an inch or two long. Each end is metallic and the center is either ceramic or glass.
To get to the fuse, remove the outer cabinet of the unit, which is usually held in place with a few screws. Once the outer cabinet is removed, follow the power cord into the unit. It will take you to the fuse holder, where the fuse sits. The fuse holder is located two or three inches into the unit, and may be attached to a power board.
Decide if your fuse is blown. A blown glass fuse will produce flash burn marks on nearby surfaces, or it will be completely black on the inside. The internal fuse wire (filament) will be melted and blackened. Ceramic fuses give no outward signs of having blown. To determine if a ceramic fuse is blown, test it with an ohmmeter. If the ohmmeter reads zero ohms, your fuse is fine. A reading of infinite ohms means your fuse is blown.
Replace the blown fuse. Pop it out of its holder and snap in a new one. You can squeeze the fuse clips together with your fingers in order to tighten their grip. Replace the unit's outer cabinet, plug it back in, and test to see if it is running properly. DO NOT run the microwave with nothing in it.
NOTE: Fuses do not usually blow on their own. A fuse may blow because of problems with the interlock switches or with high voltage circuitry. It is also possible, though rare, that a power surge will cause a fuse to blow.

Yes, there should be a ceramic (tubular) fuse under the cover on the top side where the power comes into the microwave.

Yes, there should be a ceramic (tubular) fuse under the cover on the top side where the power comes into the microwave.

Yes, there should be a ceramic (tubular) fuse under the cover on the top side where the power comes into the microwave.