Cause 1

Stirrer Motor

The stirrer is a metal blade which slowly rotates inside in the microwave. As the stirrer turns, it deflects the microwave energy randomly throughout the microwave. As the stirrer motor wears down, it begins to make grinding noises. To determine if the stirrer motor is worn out, check to see if voltage is getting to the motor. If the motor has the proper voltage, but is noisy or won’t turn, replace it. (Note: Proper voltage can be determined by reading the label on the motor. Because the stirrer motor is a geared motor, the shaft will not spin freely.)

Cause 2

Exhaust Fan Motor

To determine if the fan motor is defective, remove the fan motor from the microwave and try turning the fan blades by hand. If the blades do not turn freely, replace the fan motor. If the fan blades do turn freely, use a multimeter to test the motor for incoming power and for continuity. If the motor has power but won’t run, replace it. If the motor does not have continuity, replace it.

Cause 3

Magnetron

The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. Under normal circumstances, the magnetron emits a low hum. However, if the magnetron is damaged or nearly burned out, it may begin emitting high-pitched sounds or growling noises. If the magnetron is noisy, this indicates that the magnetron is nearing the end of its life or might be defective. A defective high-voltage diode can also cause the magnetron to be loud. Before replacing the magnetron, first test the high voltage diode. If the diode is not defective, replace the magnetron. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the magnetron.)

Cause 1

Magnetron

The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the magnetron burns out, the microwave won’t heat. The magnetron is not repairable—if the magnetron is burned out, you must replace it. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the magnetron.)

Cause 2

Door Switch

Most microwaves have three or four door switches. When the microwave door closes, the door switches actuate in sequence to ensure that the door is closed properly. If any of the door switches fails, the microwave will not start or heat. To determine if any of the door switches are defective, use a multimeter to test each of the switches for continuity. If any of the door switches does not have continuity, replace it. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace a door switch.)

Cause 3

Diode

The 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 to heat the food. If the diode burns out, the magnetron won’t receive enough voltage to operate, preventing the microwave from heating. When the diode fails, it is often visibly burned out. Inspect the diode and if the diode is burned out, replace it. If inspecting the diode proves inconclusive, test it with a multimeter that uses a 9-volt battery or put a 9-volt battery in series with the diode. When the leads are reversed, the diode should only have continuity in one direction. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the diode.)

Cause 1

Main Control Board

The main control board might be defective. However, this is not usually the case. Before replacing the control board, first check the exhaust fan motor and wiring. If the exhaust fan motor is not getting power, the main control board might be at fault.

Cause 2

Thermostat

The thermostat monitors the air temperature and turns on the fan when necessary. If the thermostat is defective, it won’t turn on the exhaust fan at all. Use a multimeter to test the thermostat for continuity. If the thermostat does not have continuity, replace it.

Cause 3

Exhaust Fan Motor

To determine if the fan motor is defective, remove the fan motor from the microwave and try turning the fan blades by hand. If the blades do not turn freely, replace the fan motor. If the fan blades do turn freely, use a multimeter to test the motor for incoming power and for continuity. If the motor has power but won’t run, replace it. If the motor does not have continuity, replace it.

Cause 1

Thermal Fuse

The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. The thermal fuse cannot be reset—if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse.)

Cause 2

Main Control Board

The main control board might be defective. However, this is rarely the case. Control boards are often misdiagnosed—check all of the more commonly defective parts. If you have determined that all of the other components are working properly,replace the main control board. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the main control board.)

Cause 3

Line Fuse

If too much current passes through the microwave circuitry, the line fuse will blow. If the line fuse blows, the microwave won’t start. To determine if the line fuse is at fault, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. In addition, you should investigate and resolve the problem that caused the fuse to blow. If you don’t resolve the underlying issue, the new fuse will blow too. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the line fuse.)

Cause 1

Door Latch

Inspect the door latch for damage. If the door latch is broken, replace it.

Cause 2

Door Spring

Inspect the door spring for damage. If the door spring is broken, replace it.

Cause 3

Open Lever

Inspect the open lever for damage. If the open lever is broken or damaged, replace it.

Cause 1

Light Socket

Before replacing the light socket, replace the light bulb. If you replace the light bulb, and the light still doesn’t work, use a multimeter to test the light socket for continuity. If the light socket does not have continuity, replace it.

Cause 2

Main Control Board

Before replacing the control, check the light bulbs, sockets, and wiring. If these parts seem to be working properly, test the control board with a multimeter to determine if it sending the correct voltage to the light bulb socket. If the control board is not sending enough voltage to the light bulb socket, replace the control board.

Cause 3

Light Bulb

The light bulb itself might be burned out. Replace the light bulb before replacing any of the parts associated with the light bulb

Cause 1

Rack Support

The paint on one of the rack supports might be chipped. Inspect the rack supports for any spots where the paint has chipped. If there are any damaged spots, repaint them with microwave-safe paint. If the rack support is burnt, replace it.

Cause 2

Paint

The paint on the interior of the microwave might be chipped. If the paint is chipped, the interior metal will be exposed, causing the microwave to spark or arc. Check the interior of the microwave for any spots where the paint has chipped away. If there are any damaged spots, touch them up with microwave oven paint.

Cause 3

Waveguide Cover

The waveguide cover might be damaged and shorting out. Try removing the waveguide cover and see if the problem resolves. If the waveguide cover is burnt or will not stay in place, replace it.

Cause 1

Touchpad and Control Panel

To determine if the touchpad and control panel are defective, try pressing each of the buttons on the control panel. If some of the buttons respond correctly while others don’t, replace the touchpad and control panel.

Cause 2

Main Control Board

Control boards are often misdiagnosed—before replacing the control board, first check more commonly defective parts, particularly the door switches. If all of the other components are working properly, replace the control board.

Cause 3

Door Switch

A door switch might be failing intermittently. Check each of the door switches for signs of overheating, arcing, or burning. If you don’t see any obvious signs of failure, use a multimeter to test each switch for continuity. If any of the switches is visibly damaged or only has intermittent continuity, replace it.

Cause 1

Main Control Board

First, make sure that the touchpad is working properly. If the touchpad is working properly, the main control board is likely at fault. If the control board is defective, replace it.

Cause 1

Glass Tray Support

If the microwave turntable is not turning the glass tray support could be broken or stripped out. Gently pull the support off the drive motor shaft to inspect the tray support for damage.

Cause 2

Glass Tray Drive Coupling

If the microwave turntable is not turning the glass tray drive coupling could be broken or stripped out. Gently pull the coupling off the drive motor shaft to inspect the drive coupling for damage.

Cause 3

Turntable Motor

Use a multimeter to test the motor for continuity. If the turntable motor does not have continuity, replace it.

Cause 1

Display Board

If the display isn’t working at all, either the main control board or the display board could be at fault. If the display goes out partially, the display board is more commonly at fault.

Cause 2

Main Control Board

If the display goes out partially, the display board is more commonly at fault. If the display isn’t working at all, either the main control board or the display board could be at fault.

Cause 1

User Control and Display Board

To determine if the control and display board is defective, try pressing each of the buttons on the control panel. If none of the buttons are responding correctly, replace the user control and display board.

Cause 2

Touchpad

To determine if the touchpad is defective, try pressing each of the buttons on the control panel. If some of the buttons respond correctly while others don’t, replace the touchpad.

Cause 3

Touchpad and Control Panel

To determine if the touchpad and control panel are defective, try pressing each of the buttons on the control panel. If some of the buttons respond correctly while others don’t, replace the touchpad and control panel.