Our 1999 Airstream had a Sharp convection microwave. It died during this year's Thanksgiving holiday.
I removed it and did some limited checking inside with the volt-ohm meter. There is a major fuse along with some other switches. All checked ok as far as I could tell. Time to declare it dead.
Sharp doesn't make a convection microwave any more. And other units, besides being very pricy, would require quite a lot of modification to fit them into the cabinetry.
So, given that we'd not really used the convection part of the machine, we went with the Sharp non-convection microwave.
The new microwave is close to the original in size, so I was able to modify the original mounting kit and reuse it. Now we have a microwave, but no convection.

Lynn