If the model number is correct, there is a 125V, 20 AMP line fuse inside the microwave. Its usually mounted at the point where the power cord enters the back of the unit. You will need to UNPLUG the microwave oven and remove the exterior case to access. The case comes off in various ways depending on manufacture and model. I found this illustration at pcappliancerepair.com based on the model number you listed this question under:
The line fuse is listed as item 12.
You can usually purchase a box of fuses at a hardware store for just a little more than what the manufacturer charges for a single fuse. 125V, 20AMP Ceramic Slow Blow fuses are recommended.
If you have any questions, or need additional assistance troubleshooting, please post back and let me know. I hope you find this information helpful.
NOTE: Make sure you take any resistance readings with the microwave UNPLUGGED and the component under test isolated (removed) from the circuit.