Microwave oven fault: blown high-voltage fuse. Before replacing, check (dirty/burnt mica sheet).

ID: 213221

Description:

Steps:

1. Common failure in microwave ovens; it TURNS ON, BUT DOES NOT HEAT. The 1st thing to check is the condition of the High Voltage fuse, which will almost certainly be burnt or blown.
2. The 1st thing is to replace the blown HV fuse. It may have blown due to simple wear and tear, or because you have a faulty component. Apart from replacing the fuse, BEFORE testing the microwave again, 2 things must be checked. ATTENTION: this is a mandatory basic check to avoid sacrificing a new fuse.

3. In this type of housing shown in the photos, it is sometimes very difficult to extract the damaged fuse; we will have to use pliers to help us.
4. We will replace the fuse with one of the same size and specifications, with a maximum of 0.9A.

5. 1st Check the MICA plate on the right side of the cooking chamber for dirt and burnt areas. Look to see if the mica is blackened; if so, remove it and clean it. If it is severely burnt and black, it will cause sparks and strain the oven's operation, blowing the fuse. As you can see, this was the problem in this case.
6. The mica plate is a protective element against food splatters in the magnetron waveguide. These splatters dry out, carbonize, and generate sparks. If the plate is in very bad condition, you can use the oven for a few days without the mica plate until you buy a new one. It does not affect its operation.

7. In this case, the mica plate was not replaced because it was damaged on one side, not in the center. My friend, whom I advised on the repair, took it out, cleaned it, and swapped the insertion side of the plate (top right to bottom left), cleaned it, and trimmed away the scorched area as much as possible.
8. For the scorched area on the metal, I advise cleaning the metal thoroughly so that no carbon residue or scorched areas remain.

9. After checking the mica plate, the second thing to check is the magnetron. Remove its connector and the 4 screws securing it (some have a thermostat with 2 wires on top). It is the large metal piece that generates the microwaves; its antenna may be burnt or deformed (although if this happened, you would have heard and seen sparks in the cooking chamber).
10. A damaged magnetron and mica plate often go hand in hand, with the mica plate being black and burnt. If it is not cleaned or replaced and the oven continues to be used for a few days, it ends up damaging the magnetron (by burning the antenna), significantly increasing the cost of the repair.

11. In this instance, replacing the HV fuse and removing-cleaning the MICA plate solved the problem. If the fuse had blown again when testing the microwave, the next guide step would be to check the capacitor, which I cover in another guide. AS THIS IS A DANGEROUS SUBJECT AND REQUIRES SAFETY PRECAUTIONS.
12. End of Guide.
13. Other guides on microwave ovens. Microwave Oven

14. Note: Although this is a general-purpose document and the procedure applies to most microwaves, as was my intent when creating the document, the fault occurred in an Orbegozo Grand gourmet microwave.