GE Microwave Oven - total failure

The GE Microwave oven JVM230 made a pop sound while cooking and died. We noticed that the 20V fuse looked blown, so we tried replacing the 20V, but it immediately blew as well.

What next? (I noticed that some people who had the same problem mentioned trying to replace something like a "thermidor", but when I looked for such a part, it did not seem to exist.

Is this a known problem with a straightforward solution, or do we need to buy a new microwave?

Thanks so much for sharing your knowledge.

Blue Skies,

Anne