above: Microwave oven components, including:
- Oven thermal cutoff
- Oven light
- Door
- LED display window
- Keypad
- Wave guide
- Door switch
- Magnetron
- Fan
- Diode
- Capacitor
- Power cord
- Transformer
- Fuse
- Monitor switch
- Door switch
- Electronic control board
Note: Details of repair and disassembly may vary, depending on appliance model. If your microwave oven differs markedly from this one, see Appliance repair basics.
A microwave oven bombards food with electromagnetic energy. This causes the food molecules to vibrate, generating internal heat from friction.
If a unit won’t work or performs erratically, check its safety devices. These typically include a fuse that blows if there’s a power surge or overload, a thermal cutoff that opens if the oven gets too hot, and a cut off that opens if the microwave-generating magnetron overheats. To keep the oven from running with an open door, most units have two door switches and a monitor switch that blows the fuse if they fail. If one device is defective, test all the others also. The fan, turntable, capacitor, and diode are also serviceable. The capacitor, which stores high voltage, is potentially dangerous. Discharge it be fore touching any internal parts. Try testing a mechanical timer; have an electronic control board serviced by a pro. Also have a pro fix the magnetron and (because of possible microwave leaks) the door.
Test temperature probe in boiling-hot water. Set VOM on RX1O; touch shaft and tip of plug. Look for moderate resistance, moving to infinity as water cools.
Gaining access:
To remove cabinet, unplug oven. Remove screws securing cabinet to back and bottom. Then slide cabinet toward back while lifting up the rear. If cabinet is hard to remove, check for screws under plugs on the top or sides. CAUTION: Discharge capacitor before touching any internal parts.
To reach turntable motor, turn the microwave oven upside down on a towel, then unscrew the motor housing from the bottom of the oven and lift it off.
Troubleshooting:
SYMPTOM: |
POSSIBLE CAUSE: |
SOLUTION: |
Won’t run Runs but doesn’t cook Keeps blowing fuses Cooks intermittently Cooks slowly Cooks unevenly
|
Power off at outlet or faulty power cord Blown appliance fuse Faulty door interlock switch Faulty fan motor Faulty mechanical timer Faulty door latch spring or control board Faulty capacitor or diode Faulty thermal cutoff Faulty transformer or magnetron Faulty door interlock or monitor switch Faulty capacitor or diode. Faulty magnetron Faulty door interlock switch Misaligned door or door seal Loose or faulty wiring connection Faulty mechanical timer Faulty magnetron or control board Low voltage at wall outlet Faulty magnetron Faulty turntable motor Loose or damaged wave guide |
See General Troubleshooting. Test and replace Test and replace Test and replace Test and replace Have serviced. Test and replace. Test and replace. Have serviced. Test and replace. Test and replace. Have serviced Test and replace Have serviced. Check and repair. Test and replace Have serviced. Remove other appliances from circuit. Have serviced. Test and replace. Have serviced. |
[Degree of difficulty: Simple --- Average---Complex --- Volt-ohm meter required]
Fuses, cutoffs, and safety switches:
Test thermal cutoff for oven or magnetron with VOM on RX1. Remove a lead and probe both terminals. Replace if reading is not zero.
Remove fuse with fuse puller, gently pry out with screw driver. To test fuse, set VOM on RX1 and probe each end. Replace if reading is not zero.
Test each door switch with VOM on RX1. Remove a lead and probe both terminals. Look for infinity reading when door is open, zero when closed.
Test monitor switch with VOM on RX1. Remove one lead and probe both terminals. Look for zero with door open, infinity when closed.
Fan and turntable motors:
Test fan motor with VOM on RX1 (or RX100 for some small motors). Remove leads and probe both terminals. Look for reading of moderate ohms. Replace motor if reading is infinity.
Test turntable motor with VOM on RX1 (or RX100 for some small motors). Remove a lead and probe both terminals. Look for moderate ohms. Replace if reading is infinity.
Capacitor and diode:
To test capacitor, first discharge it. Take off leads. With VOM on RX100, probe terminals. Look for low ohms increasing toward infinity. Reverse probes; look for same results.
To test diode, discharge capacitor. Disconnect diode from capacitor and cabinet. With VOM on RX100, probe wires; then reverse probes. One reading should be infinity; the other, low ohms.
Ultimate Guide to Troubleshooting & Repairing Microwave Ovens
