Your Microwave Oven Is Not Turning On

Can't get your microwave to operate any more? This could be being caused by just one component or by several at the same time. In this troubleshooting guide, we explain and detail the parts you need to check in order to resolve this issue.

THE POTENTIAL CAUSES FOR THIS FAULT:

• There is an issue with the electricity supply to the appliance

• The fuse has blown

• The door safety latch is broken

• The magnetron has an electrical leak

• The capacitor is faulty

• The high voltage diode is short-circuiting

• The transformer is faulty

• The safety thermostat has tripped

• The timer is jammed

• The main circuit board (PCB) is faulty

WARNING
We recommend adopting a very cautious and safety-conscious approach if you need to take your microwave apart at any point.
Microwave ovens produce powerful electrical discharges that can potentially be fatal.
Never test and use a multimeter on the appliance with it still plugged into the mains. The voltages on either the magnetron, transformer or capacitor may be too high for the multimeter to cope with.
Even when unplugged, the capacitor inside the microwave oven can still produce power electrical discharges.
We therefore recommend you leave the appliance to discharge for at least one day before taking it apart.
When you first open the microwave up, make sure you short circuit the capacitor using a pair of electrically insulated pliers (with the appliance unplugged from the mains of course).
We also recommend wearing a pair of electrically insulated gloves to ensure you are able to work in complete safety.
Carrying out repairs on a microwave oven requires a very careful and safety conscious approach. SOS Accessoire cannot be held responsible for any accidents that may occur.

There is an issue with the electricity supply to the appliance

It may the electricity supply that's preventing your microwave from operating. We recommend taking a quick look at the socket to see if it's melted. If you find you can't unplug the plug, you'll need to switch the electricity off and try applying a little force. The plug and socket could have fused together, which will prevent your microwave from operating. Check that the socket itself is working by, for example, plugging a different appliance into.

The fuse has blown

The fuse on a microwave serves to protect the appliance and keep it safe. Fuses are the main causes of faults on microwaves. If one of your microwave's components develops a fault, the fuse will blow and prevent the appliance from operating. Check the fuse's condition and, if necessary, replace it. Before carrying out any work on your appliance, however, carefully read through the safety instructions provided above. The fuse is fitted inside the microwave's outer casing and will normally be located just after the point where the power lead enters the appliance.

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The door safety latch is broken

The door safety latch mechanism on your microwave contains several small switches. If any of the door latch hooks is broken or any of the switches is faulty, the appliance will not operate. This could also cause the microwave's fuse to blow, or trip your circuit. You can test the door latch using a multimeter in ohmmeter mode, first with the door in its open position , then with it closed. Open up the top panel of your microwave and locate the door latch microswitches. Disconnect all the electrical connectors and place the multimeter's two probes on the microswitches' terminals. You should get a value in one of the two positions of each switch (i.e. door open or door closed).
Make absolutely sure you remember to follow the safety instructions provided at the beginning of this article when carrying out this operation.

The magnetron has an electrical leak

The magnetron sits inside the microwave's outer casing. It is powered by the electrical current supplied to the appliance and emits electromagnetic waves. If it has an electrical leak or becomes defective, it won't be able to work properly and may make a noise before eventually failing completely. Important: do not forget to follow the safety instructions provided at the beginning of this troubleshooting guide. Before carrying out this test, check your multimeter is definitely set to "Ohms Ω". To take the measurement, disconnect the magnetron's connectors and place the multimeter's probes on its terminals. If you obtain a value of around zero (less than one ohm), the magnetron is working correctly and is not the source of the fault. To verify the result, also check to see if there is any current leaking anywhere. To do this, place the tip of one of the multimeter's probes on the outer metal casing of the magnetron and the other probe on one of its connection terminals. Repeat the operation for each terminal. If you do not obtain any values, this confirms there is no electrical leak. Never test these components without first disconnecting the appliance from the electricity supply and discharging the capacitor. There is a risk you could get electrocuted. Replace the magnetron if your tests prove it to be defective.

The capacitor is faulty

The capacitor stores up electricity in order to amplify the voltage. If it's defective, the appliance will first generate a lot of noise when operating, then stop working, and finally end up blowing its fuse. Never check the capacitor without first discharging it and unplugging the appliance from the electricity supply. There is a risk you could get electrocuted. Follow the safety instructions we've provided at the top of the page. To test the capacitor, disconnect its connectors and place the tips of your multimeter's probes (in ohmmeter mode) on its terminals. You should obtain a value that either gradually increases or gradually reduces. If this is not the case, the capacitor will need to be replaced.

The high voltage diode is short-circuiting

The high voltage diode is made up of a stack of eight diodes. Due to this stacking, the HV diode cannot be checked with a multimeter. One end of the HV diode connects to the capacitor and the other to your microwave's chassis ground. If the diode is short-circuiting or leaking electricity, your appliance may make a loud noise and could end up blowing the fuse or tripping the circuit

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The transformer is faulty

The transformer takes a 230 volt supply and converts it to 2,200 volts in order to drive the magnetron. If it's defective, the microwave will make a lot of noise and may trip the circuit or blow its internal fuse. If this happens, your microwave will no longer operate.

The safety thermostat has tripped

The safety thermostat prevents your microwave's magnetron from overheating by cutting its electricity supply. There will be a fan fitted near the magnetron in your microwave. Check it's working properly to ensure it's not the source of the overheating issue.

The timer is jammed

Your microwave's timer will be either mechanical or electronic in design. If the timer is jammed or its internal electrical contacts are damaged, your microwave will no longer be able to operate. Your can change this component yourself. However, make sure you familiarise yourself with the safety instructions provided at the beginning of this troubleshooting guide before proceeding.

The main circuit board (PCB) is faulty

The main circuit board manages all your microwave's functions (heating, element, light, etc.). If everything else detailed above has been checked and the problem still persists, it could be that the circuit board needs replacing. You can do this yourself, as long as you carefully follow the safety instructions provided at the beginning of this article. Alternately, you can call on the services of a manufacturer-approved engineer.

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