The microwave oven was invented in (drum roll) 1945! And the first commercial microwave was sold nine years later. It was another 13 years, in 1967, before they were put on the market to households. And another dozen years before they started to become widely popular. Today, microwave ovens are in 90 percent of all U.S. homes. Fortunately, they are virtually trouble free. When they are not, here are some things you can do about it.

How Does It Work?

A microwave oven is an appliance for heating and cooking food more quickly than a conventional oven. A magnetron inside the oven produces a beam of electromagnetic waves, called microwaves. The beam is reflected throughout the microwave to heat the food. The magnetron is powered by a transformer, capacitor (dangerous!), and diode, which convert household AC power into the high-voltage DC power that the magnetron needs. Controls tell the magnetron how long to stay on and at what power setting.

What Can Go Wrong?

Fortunately, microwave ovens are nearly trouble free. Many of the problems can be fixed by the owner. For example, the power cord can be damaged, the interlock switch, thermal cutout, fan, turntable motor, temperature probe, or light bulb may need to be replaced, or the door may not close properly.

Caution!

Never attempt to service the magnetron in a microwave oven. It is extremely dangerous.

How Can I Identify the Problem?

If the microwave will not work at all, make sure power is on at the outlet and test the electrical cord. Test the fuse and replace it if it is faulty. Also check the door to make sure it closes properly. Test and, if needed, replace the fan.

If the oven doesn't cook or cooks only intermittently but the display is on, check the door interlock switch, the thermal cutout (see the Applaince Controls Fix-It Guide), and the fan, replacing parts that don't pass the test.

If the oven keeps blowing fuses, check for a faulty door interlock or monitor switch.

If the carousel won't turn, inspect the plastic coupling beneath the tray. Check the roller assembly and make sure the tray is sitting level on the turning mechanism.

If you still have trouble with the microwave, take it to a repair center that works on microwave ovens.

Fix-It Tip

Microwave cases typically are fastened together using Torx tamper-resistant screws. You'll need a special screwdriver or hex bit to remove these fasteners. Make sure you get the correct size because there are at least seven sizes. Make an imprint of the screw with some clay and take it to a large hardware or auto parts store.

What Parts, Materials, and Tools Do I Need?

You can find replacement parts from the manufacturer or from aftermarket suppliers. Tools you'll need to disassemble and test a microwave oven include these:

• Screwdrivers
• Wrenches
• Multimeter

What Are the Steps to Fixing It?

Check the door latch to make sure that it is tight and works freely.

Service a microwave oven door:

1. Inspect the door for obvious problems, such as broken components.
2. Inspect and clean the door seal along the inside front edge of the oven. Use a mild detergent in warm water; rinse and dry before use.
3. Inspect the door hinge to ensure that it isn't damaged.
4. Inspect the door latch on the outside and inside of the door to make sure it works smoothly and that it is not blocked by baked-on food.

The magnetron is the main component of a microwave; don't attempt to service it. Leave that job for a trained appliance technician.

Disassemble a microwave oven:

1. Unplug the microwave oven and remove all trays or carousels inside the oven cavity. If the unit is built-in, remove fasteners (typically on the underside of the cabinet) holding the unit in place and remove the microwave oven.
2. Turn the unit on its back or side and remove screws or bolts that hold the housing to the frame.
3. Carefully remove the housing and set it aside to access components within the microwave.
4. Identify the capacitor (see the owner's manual) and make sure you don't touch it. Capacitors hold an electrical charge after the appliance is unplugged.
5. Inspect and, if needed, clean switches and other simple components. Don't disturb the magnetron (probably encased in a secondary housing).
6. Test the electrical cord , fan, fuse , interlock, and other appliance components.
7. Reassemble and test the microwave oven.

DON'T TOUCH the capacitor!

Test a temperature probe:

(Temperature probes have two ends: a sensor end that measures temperature and a connection end that delivers the results to the microwave.)

1. Place the temperature probe's sensor into a cup of hot water.
2. Set the multimeter to measure resistance (RX1, or resistance times 1 scale).
3. Place the multimeter's test tips on each side of the temperature probe's connection end. The resistance (in ohms) should be more than zero but less than infinite. If infinite, the temperature probe isn't sending a signal to the microwave; replace the probe with an identical part.
4. If the temperature probe is okay, the control board inside the microwave may need to be replaced. Take the microwave oven to a service shop for repair.

Fix-It Tip

A microwave's fuse typically is located inside near the electrical cord. You can test and replace it.

Microwave ovens are heating appliances of 500 to 1,500 watts. Make sure there is sufficient ventilation space around a microwave to keep it relatively cool. Manufacturers typically suggest at least two inches of clearance behind and beside the microwave oven. Check the unit's owner's manual for specifics.