Ultimate Guide to Troubleshooting & Repairing Microwave Ovens -- Index

HOME | Troubleshooting | DIY Tips

  • 1 Some basic facts
  • 2 Required tools and test equipment
  • 3 Microwave oven circuits
  • 4 Basic troubleshooting procedures
  • 5 Troubleshooting microwave oven switches
  • 6 Servicing low-voltage circuits
  • 7 Troubleshooting high-voltage problems
  • 8 Locating and replacing defective magnetron
  • 9 Servicing oven motors
  • 10 Servicing control circuits
  • 11 Microwave leakage tests
  • 12 Microwave oven case histories
  • 13 Important do’s and don’ts
  • 14 Where and how to obtain parts


The microwave oven is here to stay. It’s used every day in just about every home in America and all over the world. The microwave oven can be found in the kitchen, den, cottage, motel room, and motor homes. Who expected the microwave oven to be used as much as a TV receiver? People who own microwave ovens cannot do without them. The oven is used in preparing breakfast, lunch, dinner, and sometimes in-between snacks. The microwave oven has become an integral part of our lifestyle.

Printed circuit boards were supposed to solve many wiring problems because small transistors were designed to never break down. Like the microwave oven circuits, printed circuit boards were designed for single and trustworthy operation— except that whenever you place mechanical and electronic components into a commercial unit, sooner or later you are going to encounter service problems. Like the TV chassis, microwave ovens are constructed better today and have less break downs. But when the oven quits, the customer wants it back yesterday.

Many ovens can be repaired by simply changing the ac line fuse. Of course, even replacing the fuse requires removing the back cover. These oven fuses are chemical types, in ceramic sleeves, so you cannot peek inside to see if they have blown open. Often, the monitor switch hangs up, line voltage overloads, or nearby lightning dam ages or opens the fuse. Whatever the breakdown, you should have a low-priced digital multimeter (DMM) to check for a defective fuse or poor interlock switch contacts.

Just about anyone can make basic repairs to the microwave oven using a few hand tools and the DMM found around the house or on the service bench. Defective fuses, interlocks, motors, fans, transformers, switches, and components in the low- voltage circuits can be checked with a little knowledge and the digital multimeter. Never place tools or hands into the oven while operating. Remember, these low-volt age parts operate from the ac power line. Treat the 120 volt ac circuits with extreme care. Leave the high-voltage problems up to the professional electronics technician. A Magnameter and leakage equipment should be used to locate the defective components in the HV circuits.

Always make sure to discharge that high voltage capacitor! Before replacing or attempting to service the microwave oven, discharge the fly capacitor. This capacitor can hold a charge for several weeks in some ovens, so discharge the high-voltage capacitor every time the oven is fired up. You can receive a shock of more than 3000 volts, which can injure or seriously damage a person. Remember, besides high-voltage, the amperage is very high in the magnetron circuits. Discharge the Fly capacitor with a pair of long, insulated screwdrivers. Servicing microwave ovens can be extremely dangerous if you don’t know what is going on.

The microwave oven has gone through many changes in the last 30 years. Yesterday, all ovens were manually operated. Today, practically all ovens are operated with touch pads and control panel, like those found on a calculator or computer. The new microwave oven has many circuits on time, different foods, preheat, and defrost pads. Cooking begins and shuts off automatically for the selected time. Some ovens have variable-power cooking when touching the power level several times to select high, medium-high, medium-low, and low power. Multiple sequence cooking can be programmed for several cooking sequences, switching from one variable-power set ting to another automatically. The electronic control brain provides a variety of cooking programs—and all are controlled with a microprocessor in the control panel.

In this guide, valuable service information, data, and drawings of the General Electric, LG, Panasonic, and Samsung ovens are found scattered throughout the guide. Each page has either a photo or drawing to illustrate the many oven components and circuits. Every component is shown, and you are instructed as to how to test, isolate, and replace each oven part. Although it’s impossible to deal with every trouble found in microwave ovens, you will find that the great majority of problems are covered and resolved in this guide.

The latest circuit diagrams, data, valuable service information, and drawings of General Electric, Siemens, Panasonic, LG, and Samsung ovens are scattered throughout the guide. Fifteen different ovens with symptoms and troubleshooting methods are found in over 250 case histories. In my 45 years of experience in troubleshooting and repairing microwave ovens, I’ve encountered almost every problem found in such ovens, and these potential problems are all covered in this guide.

Sections 1 through 4 cover how the low-voltage circuits operate, with new required test equipment, and every kind of trouble. Section 5 shows how to troubleshoot those interlock switches with Sections 6 and 7 discussing the high voltage circuits. How to locate, remove, and install the magnetron tube is explained in Section 8. How to service motors is explained in Section 9. How to locate and remove the defective control board circuits are discussed in Section 10. Section 11 explains how to tell if the microwave oven is cooking as it should. More than 250 actual oven case histories are found in Section 12. This section alone can help solve the many different microwave oven problems you may encounter every week. Some important do’s and don’ts are listed in Section 13. Where to locate and find the microwave oven parts and manufacturers is given in Section 14.

The first, second, and third editions have gone through many printings. I have updated all the sections and included new test instruments and oven service data. The new General Electric tilt-down oven-door oven, Samsung, and Sharp latest ovens are found in this edition.

New methods of servicing the microwave ovens, new circuits, and required test instruments are found throughout the guide. How to service the convection oven is found in Section 6, and Section 10 covers the latest control board troubleshooting data. You will find more than 500 illustrations in this guide, and several microwave oven schematics. Just be sure to remember the danger involved in repairing microwave ovens.

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