How to Fix a Microwave

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How to Fix a Microwave

A person might look at a broken microwave oven and see a lost cause. Microwave ovens seem to rely on technology that is more complicated than other things that can be fixed by do-it-yourselfers. However, there are many problems that can be fixed without calling the repairman. This guide will provide an overview of microwave technology and look at a number of relatively simple fixes for common problems with microwave ovens. To get parts for a microwave oven, one could go to a hardware or home improvement store. Microwave ovens can also be purchased at most electronics and department stores. However, if a person were to look online for microwave ovens or parts, then eBay is the best place to go. The site has parts for microwave ovens of all types and manufacturers. Consumers can also find excellent bargains on a wide array of helpful products to use with microwave ovens.

A Crash Course on Microwaves

A microwave oven works by using radiation to provide dielectric heating for polarized molecules in food. The radiation excites the electric dipole molecules (often water) and food is heated evenly, unless the food is dense and thick. Radiation used in microwave ovens is between common radio and infrared frequencies. When heating water, microwave heating if more efficient on liquids than solid ice because the water molecules in ice are more restricted. Sugars, fats, and oils (sometimes triglycerides) absorb microwave radiation and sometimes attain much higher temperatures inside microwave ovens.

Design of Microwave Ovens

Now that the theory behind microwave ovens has been briefly explained, a look at how the mechanics of microwave ovens will be presented. The following table provides an overview of the six essential parts of a microwave oven.

Microwave Oven Part


High voltage power source

Passes energy to the magnetron

High voltage capacitor

Stores energy in an electric field

Cavity magnetron

Converts electric energy to microwave radiation

Magnetron control circuit

Controls the magnetron in terms of power level


Controls the direction of the microwaves

Cooking chamber

Provides radiation-proof area for food to be warmed

Knowing these main components is crucial for anyone wishing to perform his or her own repairs to a microwave oven.

What to Do Before Looking Inside a Microwave Oven

Before examining the innards of the microwave, there are a few simple checks that a person can perform to make sure that the problem is not external. If the microwave does not turn on, the user should make sure the oven is plugged into an outlet adequately. The door should close completely with its latch aligned and the interlock switch in the door should be properly engaged, because it is required to activate the oven. If the microwave has a turning mechanism, the tray can be examined to ensure that it is properly aligned.

First Steps When Working on a Microwave Oven

When examining a microwave, there are a few steps that need to be taken before work is done. First, the microwave oven must be unplugged before the microwave is opened. Before troubleshooting any appliance, it should be disconnected from its power source. The microwave should also be cleaned because food residue and burned spots can cause electrical arcing. Burn spots can be sanded. Wave guides can also become burned or carbonized. If this is the case, they should be replaced.

Discharging the Capacitor

In addition to unplugging the microwave oven, one must discharge the capacitor. Because the capacitor stores energy, it can be a safety hazard even when the microwave oven is unplugged. To discharge the capacitor, a jumper wire with an alligator clip on one end should be clipped to each end of a wire-wound resistor with a two-watt, 20,000 ohm rating. Another clip should be added to the metal shaft of a screwdriver as a grounding element. The last wire should be clipped to the one of the capacitor's terminals. The other terminal should be touched with the tip of the screwdriver. A small spark will be discharged. If the microwave capacitor has three terminals, the process should be repeated for the middle and each outside terminal.

Common Fixes for Microwave Oven Issues

There are a number of common problems with microwave ovens that can be fixed by people with a bit of technical knowhow. The following issues can often be fixed without taking the microwave into a repair shop. In order to look at the inner workings of the microwave, the outside shell will need to be removed. The shell is generally held in place via screws on the back and underneath the microwave. Once the screws have been removed, the shell can be slid off the oven.

Issue 1: Microwave Will Not Turn On

If the microwave will not even turn on, there are a number of issues that could be causing the problem. The power cord could be damaged or burned. Once the power source and cord have been examined and determined not to be the problem, a person can inspect the inside of the microwave. After the shell is removed (as above), the three most common power problems are the fuse, the door switch, and the fan motor. One will need a volt-ohm meter (VOM) set to Rx1 to inspect the sources.

The fuse can be removed from the fuse pullers and the VOM reading should be zero. With the door switch, the leads should be removed and the VOM should be used to probe the terminals. The reading should zero when the door is shut and infinity when the door is open. The same process can be used with the fan motor. Remove the leads; use the VOM to probe the terminals, and the reading should be zero.

Issue 2: Microwave Blows Fuses

A faulty door switch may be causing the microwave to blow its fuses. Other issues could be from the capacitor or diode. After discharging the capacitor as noted above, the leads can be removed and the capacitor can be probed with the VOM set to Rx100. Readings should start in the low ohms and increase toward infinity. To examine the diode, it should be disconnected from both the capacitor and the appliance. The wires should be probed with the VOM set to Rx100. One VOM reading should be infinity and the other in the low ohms.

Issue 3: Microwave Activates But Will Not Cook

When a microwave activates, but it does not cook anything, there is likely a disconnect in the internal mechanism of the microwave. Thermal cutoffs may be the culprit. They are disc-shaped devices that are connected via a wire. Both thermal cutoffs should be checked at the oven and the magnetron. The leads should be removed and the terminals probed with the VOM set to Rx1. The reading should be zero. If it is anything but zero, the thermal cutoffs should be replaced. Other issues such as the capacitor, diode, magnetron, or transformer would need be serviced by a professional.

Issue 4: Microwave Cooks Unevenly or Slowly

If the microwave cooks the food, but it is either too slow or very uneven, there may be a problem with the voltage at the outlet that is supplying the power. If the voltage is less than 115 volts, the problem is likely with the electrical service or breaker. Another potential problem is a bad turntable motor. To examine the turntable motor, the microwave oven must be turned over and the bottom grilled should be removed. Remove one lead from the motor terminals and probe the terminals with the VOM set to Rx1. The motor should be replaced if the reading is infinity.

Issue 5: Sparks are Generated Inside the Microwave

Sparks generated within the microwave can be scary and can cause fires. The sparks generally are a result of splattered food or accumulated grease within the oven. By cleaning the microwave thoroughly with a damp cloth and soapy water, these hazards can be removed. A tablespoon of lemon juice or vinegar can be added to plain water to provide cleaning. To remove caked on food, a dish full of water can be microwaved for five to ten months to provide steam cleaning.

Sparks could also be the result of a faulty stirrer or diode. If the stirrer isn't working properly, microwave radiation can be concentrated too fully on one spot. A broken stirrer is usually the result of a misaligned fan motor or broken stirrer belt. The diode could be shorted or opened. Probe the diode with the VOM set at Rx10,000 or higher. If the diode reads in the range of 50,000 to 200,000 ohms, it is working properly.

How to Find Microwave Ovens and Microwave Oven Parts on eBay

Once you have diagnosed the problem with your microwave, you can head over to eBay to find replacement parts (or perhaps a new microwave oven). To look through the site, you can either use the search engine or the category directory. For the latter, start on the home page and select the Home, Outdoors & Decor portal followed by the Home & Garden section. Then, go to the Major Appliances page, and then choose the Microwave & Convection Oven category. Microwaves are divided into Countertop Microwaves and Microwave Hoods (Over Range). There is also a section for Parts & Accessories, but this includes convection oven parts.

Search Tips on eBay

If you choose to use the search engine on eBay, here are some quick tips. The search engine does not factor in capitalization, so you don't need to worry about that. However, you do need to worry about spelling your search terms correctly. The search engine has a very limited ability to correct misspellings. If you want to search through ovens, but do not want convection results, you can use the minus sign to reduce those results. You'd type "microwave ovens, -convection" to get those narrower results. You can also search within any category to yield more precise results.


Before taking a faulty microwave oven to a repairman, there are a number of things a person can do to remedy the problem. This guide has provided an overview of how microwave ovens work and some preparatory steps before examining the inside of the microwave. A number of issues have been examined, including microwave ovens that do not have power, ovens that blow fuses and create sparks, uneven or slow cooking, and ovens that activate but will not cook.

For most of the fixes, a person will need a volt-ohm meter to examine whether the part if working properly. Safety should be priority one when examining the inside of a microwave oven because a large amount of energy is stored within. The microwave oven should be unplugged and the capacitor should be discharged before any probing is performed. Whether one needs to buy a part or two, or just get a new oven, eBay has the parts and ovens for any fix.

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