GE jvm1190 above the range microwave /convection (2001 model)

Check this ouit first before you go out and buy a new mag:
The mag's little cooling fan probably broke loose and fell off the fan motor's shaft. The fan motor will still be running when you hit start but there is no fan on it. The fan keeps the mag cooler. The mag will heat up too much in a few minutes and then shortly the oven automatically shuts everything down when the mag gets too hot because the fan blade is just lying in there, Fan needs to be glued back on the shaft after the shaft is roughed up a little. Disconnect the plug-in wires (note where they go on), wiggle and remove the fan motor from the oven. I used contact cement to hold the fan to the shaft. the fan motor is located right behind the control panel. You have to first remove the grill, then the control panel's screws. It's not difficult to repair. No new parts needed. Poor engineering design of the cooling fan shaft.

It sounds just like the magnetron is bad, overheating and opening the thermostat. This is how it would work if that were the case.

One other thing is to be sure that the cooling fan is running and that you feel air flow.

You should check the air filter and grille, as well as the outside vent for any blockage.

If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk

You can find helpful exploded view diagrams and order parts by entering your model number here: http://tinyurl.com/gv383