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. Unfortunately, you will need to uninstall the oven, UNPLUG it and remove the exterior case to access. The case comes off in various ways depending on manufacture and model. I found this illustration at searspartsdirect.com based on the model number you listed this question under:
http://www.searspartsdirect.com/partsdirect/showSubComp.pd?imageUrl=http%3a%2f%2fc.searspartsdirect.com%2flis_png%2fPLDM%2f50026410-00007.png
The line fuse is listed as item 8 (part number 3B74133K). There is a another fuse listed as item 2 (part number 3B72974C), but this is a thermal fuse for the fan motor.
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 wish to order on line, use the part numbers to search by comparison as the model number you listed this question under is not available at all the websites I have provided. The parts, however, ARE listed.
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.
To answer your initial question, "yes", these ovens can blow a fuse by simply sitting idle. This can occur from any power fluctuations, brown outs, voltage spikes, etc. Or, it could be the symptom of a component that may have failed. If you find any of the internal fuses blown and replace it, only to have it blow again, you have a more significant problem than a simple blown fuse.