To repair a microwave oven turntable, replace the coupler if it is broken, inspect the turntable motor using an ohmmeter, and purchase a new motor or control board depending on the problem. Unplug the microwave oven before attempting this repair.
Take the turntable out of the microwave, and remove the bottom part of the microwave oven. The coupler is the plastic unit that links the turntable to the motor. If the coupler is broken, purchase a new one from a home improvement store or appliance parts retailer. Restore power to the microwave, and test the microwave turntable.
If the coupler repair does not work, or if the coupler shows no signs of damage, inspect the turntable motor. Turn off the power again, and take the bottom off the microwave to access the motor. Set your ohmmeter as high as possible, and check for continuity across the motor, replacing the motor if the results show it is open. If the motor isn't open, check the voltage. If you are not qualified to work with live electricity, contact a repair professional instead.
To complete the test, turn the power back on, and set a voltmeter to the rated voltage on the microwave. Rated voltages are typically 21 or 110 volts. If voltage appears but the turntable doesn't turn, purchase a new motor. If no voltage appears, purchase a new control board.