The first thing I would do is google the model number and see if it is
one of the spacesavers that turn themselves on and catch fire. Second, a
new magnatron will cost close to 200.00 and from the reports I've read
it may not last any longer than the previous one. Try "GE microwave +
fire" on google and you will find a site that lists the model numbers
for the fire hazard models as well as the magnetron failure reports.
Good Luck