What are the 3 wires on a microwave transformer?

The MOT has three windings: the primary (at the bottom in the photo); the filament secondary (a few turns of heavy wire with leads marked A, B), and the high-voltage secondary (outer turn connected to lead C, inner turn riveted to the transformer core right above the HV secondary in the picture.

If your microwave oven doesn’t heat, you may have a problem with the magnetron. This component is part of the high voltage circuit and provides the microwaves that generate the heat. If the magnetron is defective, the unit may blow a fuse, or you may still have all other functions operating normally.

Although the average life of a magnetron tube is 22 years, a number of factors can cause that number to diminish and for the microwave oven to lose power more quickly.

If you’ve determined you need to replace your magnetron, you have two options: buy a replacement and follow the simple replacement guide- or replace the microwave altogether. A new magnetron isn’t cheap- it could run you anywhere from $100-250- more often than not equal to or greater than the cost of a new microwave.

Magnetron has seen wide adoption diverse fields. In operation, it needs dual power supply circuits: a filament power supply VF and an anode power supply VA. The filament power supply heats the cathode to produce electrons, and normally the voltage is 3.3V/10A.

No matter how new your microwave or if there’s only one problem, if the magnetron is out then you might as well replace the entire appliance. The magnetron is the heart of a microwave that actually makes the micro-waves. Replacing it is about equal to the cost of buying a whole new microwave, sometimes even greater.

Look at the multimeter’s screen and take note of the reading. If the resistance stays below 1 ohm, then the electric filament inside the magnetron functions properly. If you get a higher reading or if the screen reads “OL”, then the magnetron is faulty and should be replaced.

What does the diode do? The microwave diode converts the alternating current (AC) power output of the transformer to direct current (DC), doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron to heat the food or beverage placed in the oven cavity.

A diode is reverse-biased when the positive (red) test lead is on the cathode and the negative (black) test lead is on the anode. The reverse-biased resistance of a good diode displays OL on a multimeter. The diode is bad if readings are the same in both directions.

To test your transformer, simply touch the red and black pins of your ohmmeter to the opposite ends of the transformer’s wiring. Read the display and compare the resistance on your ohmmeter to the resistance stated on the transformer’s data sheet. This is sometimes listed on the transformer’s enclosure.

The most common reason why transformers explode and burn is accidents caused by lightning strikes. Lightning strikes can often damage the wiring and transformer equipment.

If your microwave isn’t heating, first check it’s not because of a setting (timer, low power). Switch on/off and test again with water. If it’s still not heating, common issues are door frame switches, high-voltage diode, or the microwave’s magnetron.

The average microwave oven lasts about seven years with normal use, and even less with heavy use and poor maintenance.