Our Bosch microwave turned on, but shut down after about 15 seconds, without heating. We found that the magnetron antenna and insulation was burned and cracked. So we replaced the magnetron and the microwave now works normally. I need to understand why the magnetron failed.

I wonder if the cooling fans could be malfunctioning.

After replacing the magnetron, I tested the unit and noticed that only one of the two internal cooling fans was operating - the one directed at the inverter board. The other cooling fan, directed at the magnetron was not running.

Also, there are two identical-looking components on the top housing of the microwave. One is called "limiter-temperature," and the other is called "relay." I couldn't tell which was which, but assumed the one with one wire in and one wire out was the "limiter-temperature." I tested for continuity and found it open, then tested the "relay" and found continuity.

Does this sound like the cooling fans are operating normally, or should the both run continuously. Any help would be greatly appreciated!