Appliance Repair Blog
Thoughts and commentary about appliance repair topics including common failures and repairs, plus links to frequently used parts, industry news, along with information to help you better understand your appliances. Resources available for the technical professional and the do-it-yourselfer. Over 650 Posts

Maytag Microwave no Operation

Model #MMV5207BAWicon, this over the range microwave had been working until recently. While using the unit to reheat some leftovers, the display and lights all went out as if the plug had been pulled. None of the buttons worked, and there was no indication of life coming from the display. The customer verified the outlet still had power which left the microwave itself as the problem.

Now for my microwave safety message. Microwaves are unlike other appliances in that they use very high voltages to do what they do, and these voltages can still be present even when the unit is unplugged from the outlet. It is important to understand what you are working on and be comfortable around electricity. Always assume an electrical component is energized when poking around inside. Understand your limits and seek professional advice if you are uncomfortable at all with working on a microwave.

Because this unit was acting like it was unplugged, even when there is verified voltage at the outlet, I figured it was time to go looking at the various safety components of the circuit. Microwaves, like other appliances, use thermal fuses or bi-metals designed to open an electrical circuit in the even of an over temperature condition. Typically used to prevent a fire from occurring, they can fail simply due to age, or in the case of a microwave, accidentally setting your pop tarts on fire because you set the timer for 10 minuets instead of one.

Microwaves may have more than one of these safety devised and there may even be bi-metal switches that look the same, but are designed to function in a different way. For this reason, it is always best to have a look at the wiring diagram so you know which wire colors to look for when investigating a failure. In the absence of such information, then simply checking them all for continuity will do. Just remember, not all that read as an open circuit are that way because of a failure.

Over the range microwaves can be cumbersome to troubleshoot, simply because of how they are mounted in place. To get a good idea of how everything is layed out, it is best to remove the unit from the wall and then to remove the outer cover. Most technicians don’t do it this way simply because of the time involved, but it does offer more accessibility for testing.

In my case, I removed the control panel which gives me access to just about every wire inside. From here, I started doing continuity checks with my multimeter of each thermal fuse until I found the one that failed. As expected, it was the one right on top, often called the cavity fuse or flame sensor. This bi-metal is there in case you do overheat something to the point it bursts into flames. The fuse will open cutting power to everything. And once it opens the circuit, it needs to be replaced.

The bi-metal inner workings

Looks like the unit needs to come off the wall after all. And once down and in a workable area, I made my way through all the various screws to finally get to the top of the oven cavity. Here I replaced the thermal fuseicon, then carefully proceeded to put it all back together. Before reattaching it to the wall, I plugged it in as a test just to be safe. The lights and display came to life which is a good indication I found the problem. A glass of water was put on the turntable, as a test load, and a heating test was started. After 30 seconds the water was getting noticeably hot which means it must be working. The microwave was put back in place above the range and it is now ready for those leftovers again.

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