The fuse is located to the right frontside of the blade fan (part 53 on GE diagram at https://www.geapplianceparts.com/GEApplianceParts/Dispatcher?REQUEST=ACCESSORY
The fuse iitself is part 47 on this diagram, which is housed in fuse box part 46. I used this diagram to locate the fuse. You have to get the microwave off the wall; then take off the cover; unplug a socket from power supply cord that plugs into a socket just behind the fan housing; and move the cover out of way to access the fuse house. The fuse is is 250 V , 20 AMP microwave fuse available at Home Depot for less than $3. GE price is $7.50; appliance stores will charge you about $20. Work is basic, but you need to be reasonably strong and tall to remove the microwave from the wall by yourself. If you are not six feet tall and strong; you may want to have a second person for help.
Suresh Baral
July 2011