I have a Maytag mmv4205baw Microwave oven. It

Does everything else work?? If so, its just the turntable motor, simple to replace. there are three or four screws under the bottom. UNPLUG the microwave first.

Double check before ordering...but ..
Here is the one you need:
Turntable Motor DE31 10172C

see this causes and fix it. God bless you
Diode The high voltage diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron which emits the energy that cooks the food. If the diode burns out, a lower A/C voltage reaches the magnetron, which is not sufficient to power the magnetron. When the diode fails it is often visibly burned out. If it appears to be good, it can be tested with a volt-Ohm meter capable of testing diodes. High voltage diodes frequently fail and are one of the most common points of failure in a microwave oven.

Door Switch If the microwave does not heat, one of the door switches might be defective. Microwave ovens normally have three door switches, if any of them fail the microwave does not turn on and does not heat. Check the switches for continuity with an Ohm meter.

Magnetron If the microwave oven doesn't heat the magnetron tube might have burned out. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the microwave oven is turned on when it is empty this can cause the magnetron to burn out. Once it is burned out it has to be replaced, it's not repairable.

High Voltage Capacitor If the microwave doesn't heat the high voltage capacitor might be defective. The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out the entire high voltage circuit stops working properly. The high voltage capacitor can be checked with a special VOM meter which has a capacitance testing capability. Be aware that the high voltage capacitor can retain a charge of more than 3,000 volts and can injure or kill a person if not handled properly. Only trained technicians should perform this type of testing.

High Voltage Transformer If the microwave does not heat, the high voltage transformer might be burned out. Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food.

Thermal Fuse If the microwave doesn't heat the thermal fuse may have blown. It can be tested for continuity. Watch our fuse testing video for more information.
Thermoprotector If the microwave doesn't heat the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it's blown.

Main Control Board If the microwave doesn't heat the main control board may be defective. This is not common. When a microwave doesn't heat the problem is usually within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.

If the unit operates correctly except heating the food, then the unit needs a new magnetron.

The magnetron is the likely problem, {heart of the microwave oven}

One of the micro switches has malfunctioned, and must be replaced for normal operation.

Change the turn table motor part # DE31-10172B
Order from Bi Coastal Appliance Parts @ 1-800-673-1262

There are three things that will cause this, the magnetron "common problem" or the high voltage capacitor or diode. The above mentioned work together to heat the food and depending on the nature of the repair, parts and labor can approach the price of a new unit.

The keypad controller has probably developed a short in the membrane of the keypad, it must be replaced in order to get it up and running, but I suggest a maytag repairman to address this.

Sounds like the magnetron has failed. There are some high voltage circuits that feed the magnetron and you can potentially get hurt if you don't know what you are doing. Would recommend you have it serviced by a professional if you want it fixed, otherwise look for a new one since the cost of repair can come close to the price of a new microwave oven.

The most common problem spot when the microwave will not heat is the magnetron. this is a device that produces the heating effect. you will need to replace this failed component. it has failed. Replace the Magnetron.