Where is the fuse located.
There is usually a 125V, 20 AMP line fuse inside most microwave ovens. It will be mounted somewhere at the point where the power cord enters the back of the unit, in line with the power cord, or on a small circuit card called a line filter. Unfortunately, you will need to uninstall the oven (if this is an over the range model), UNPLUG it and remove the exterior case to access. The case comes off in various ways depending on manufacturer and model. Parts are available at any of the following websites:
The first three sites include illustrated parts listings that can help you locate and properly identify any parts you may need. The microwave oven may also equipped with various thermostats that (if blown) can cause similar symptoms to that of a blown line fuse. So, if the line fuse is NOT blown, you may want to check all the thermostats to see if they are still good. You will need to remove each one and measure across the terminals with a multimeter. A good reading is 0 ohms. NOTE: The thermostats typically will trip if the oven cavity has been overheated. Cooking items that are high heat producers such as popcorn or baked potatoes in rapid succession can often cause this problem. Allowing the oven cavity to cool a few minutes with the door open between cooking can prevent this from occurring.
If the line fuse is blown, 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. These ovens can still 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 the internal fuse blown and replace it, only to have it blow again, you have a more significant problem than a simple blown fuse.