Microwave Repair Guide

Warning

Microwave repair can be dangerous! You must unplug the microwave before attempting to repair it because they use very high voltage on certain internal parts. After the microwave is unplugged you must also discharge the capacitor before servicing because the high voltage that the microwave operates on is stored in the capacitor. To manually discharge the capacitor, place an insulted handle screwdriver between the diode connection of the capacitor and ground. It should discharge itself but always discharge it manually!

In this page, I will be walking you through the steps in Microwave repair. These are the same steps I take when diagnosing Microwaves professionally. Read each section carefully and follow the steps until your problem is fixed! Your Microwave will be repaired in no time!



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Microwave Runs but Don’t Heat

In this section of my microwave repair guide, I will walk you through the steps in repairing a microwave that won’t heat.

Magnetron Tube

The magnetron tube is the most likely cause for this problem. Most magnetron tubes are guaranteed for ten years, so check your owner’s manual before you start because if it is in warranty, you should call a warranty repairman. If it isn’t in warranty, follow these steps to determine if the magnetron tube is your problem. First, disconnect power from the microwave. Then remove the case by removing all the screws around the edge of the back. Once off, you should see the magnetron tube - remove it. On the backside of the magnetron, you should see the tube then look inside the tube. If it’s burnt looking it is bad and needs replacing. If it is not burnt, it still might be bad, so follow the rest of the sections. If no other parts that are checked are bad, then replace the magnetron tube.

Magnetron Test

This section requires you to test voltage with the microwave running. Use this information at your own risk. Applance-repair-it.com is not responsible for any damages see disclaimer.

Above I describe a way to visually check the magnetron tube to see if it is bad. However this is not a 100% accurate test. Testing the magnetron tube is more or less a process of elimination. The first thing you will have to do is test to see if there is voltage going to the high voltage transformer when the microwave is running and “calling” for heat. If there is voltage going to the transformer you know the problem is in the high voltage side. Test the capacitor and the diode as described below and if they are ok replace the magnetron tube. If there isn’t voltage going to the transformer the problem is more than likely the smart board.

Magnetron tubes can be purchased at AppliancePartsPros.com. If you have a GE spacemaker Microwave that needs a magnetron tube this page will help GE spacemaker magnetron tube replacement

Diode


The diode is an electrical device that only allows electricity to pass one way. The diode is located on the capacitor. To check the diode, first disconnect power then unplug the diode from the capacitor and unscrew it from the frame. Then set your ohmmeter to the closest setting to 50,000 ohms. Then check ohms between the two ends of the diode. The diode should read nothing one way and somewhere around 50,000 ohms the other way. If the diode is bad it will read near zero ohms either way or nothing both ways. Note that some ohmmeters will not read 50,000 ohms so it will appear to be bad when you perform this test. Also note that if the diode is bad in most cases, the magnetron tube must be replaced. Diodes can be purchased at AppliancePartsPros.com.

Capacitor

Capacitors do not go bad often but to check this, first disconnect power. Then remove all the wires from the capacitor. Then use your analog ohmmeter and between the two terminals, if the capacitor is working properly the needle on the meter will move up a little then back down. If you reverse the leads it will do it again. If you have a digital ohmmeter it must have a capacitor tester in order to test this capacitor and it should read around 15 microfarads. Capacitors can be purchased at AppliancePartsPros.com.

Smart Board

The smart board can cause this problem as well but is not that common. There is not an easy way to check this so only change the smart board if you don’t find any of the other parts in this section bad. Smart boards can be purchased at AppliancePartsPros.com.

Microwave Won’t Run

In this section of my microwave repair guide, I will walk you through the steps in repairing a microwave that won’t run.

Fuse

If your microwave won’t run, the most likely problem is the fuse. To check the fuse, first disconnect power then remove the case by removing screws around the edge of the back. Once off, you should see the fuse, remove it. Then using your ohmmeter, check to see if you have continuity across the fuse. If not, the fuse is bad and needs replacing. If the fuse is blown, check the monitor switch as described below. If you do have continuity, reinstall it and move to the next part. Fuses can be purchased at AppliancePartsPros.com.



Door Switches

Microwaves have three door switches, a primary interlock switch, monitor switch and a secondary interlock switch (sometimes called a sensing switch).

These switches often go bad and are an easy do-it-yourself microwave repair. The monitor is almost always in the middle and the other two vary from model to model but don’t worry the procedure for checking them is the same.

Primary Interlock and Secondary Interlock

The primary interlock and the secondary interlock are the top and bottom switches and the procedure for checking them are the same. First, disconnect power and discharge capacitor. Then remove the wires from both of them and using an ohmmeter, check the switches. If the switches are working properly you should have continuity between the two terminals with the microwave door closed it should and it be an open circuit (no continuity) with the door open. Test both switches the same.

Monitor Switch

The monitor switch is almost always the switch in the middle. If the monitor switch fails, the fuse may blow. To check the monitor switch, disconnect power and discharge the capacitor. Then remove the wires from the switch. Using your ohmmeter check the switch. If the switch is working properly it should be the exact opposite of the other switches. It should be an open circuit (no continuity) with the microwave door closed and with the door open it should have continuity. Door switches can be purchased at AppliancePartsPros.com.

Safety Thermostat

If the safety switch is bad this will be an easy do-it-yourself microwave repair. Most microwaves have a safety thermostat that will cut off the microwave if the microwave gets too hot. Usually it is located on top of the microwave. You will have to remove the case of the microwave to access it. To check it, disconnect power from the microwave. Then remove the wires from the thermostat and check for continuity across it with an ohmmeter. If it is open replace it.

Smart Board

The smart board can cause this problem as well, but is not that common and there is no easy way to check. Only change this if you don’t find any of the other parts in this section bad. Smart boards can be purchased at AppliancePartsPros.com.

Again I can’t stress this enough Microwave repair can be dangerous! You must unplug the microwave before attempting to repair it because they use very high voltage on certain internal parts. Also always be sure the capacitor is discharged before servicing because the high voltage that the microwave operates on is stored in the capacitor. To manually discharge the capacitor, place an insulted handle screwdriver between the diode connection of the capacitor and ground. It’s should discharge itself but always discharge it manually!!

I hope this microwave repair guide helps you repair your microwave and save money.

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Appliance Repair Expert

Shawn

  • Appliance repair since 1996
  • 2-years refrigeration courses
  • 1-year electric theory courses
  • 1-year residential wiring course


Appliance Accessories And Products I Recommend

The most commonly used diagnostic tool is the ohmmeter check out this page.

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