EnglishMicrowave ovens are one of the most convenient electric methods of cooking. The microwave energy is generated by a magnetron which acts as a high powered vacuum tube. This cavity magnetron is basically a cylinder of metal with a hole through the center.
Before conducting any tests on your microwave, you must make sure it is unplugged. This is because the capacitor contains a lot of electricity.
High Voltage Control Circuit
Microwave Oven Magnetron use extremely high voltages, and any attempts to repair or troubleshoot faults must be done with the utmost care. Microwaves contain a large capacitor that stores these high voltages. It will remain charged even after the appliance has been switched off, so it is important to discharge it before attempting any repairs.
The high voltage system steps up AC line voltage to a higher voltage, then converts it to DC power. This power then flows into the magnetron tube.
The high-voltage SCR circuit provides the means for selectively supplying different amounts of microwave energy to the magnetron tube. It eliminates the need for a high-voltage rectifier or a separate filament transformer. Moreover, it is inexpensive and easy to produce. It also offers a degree of power control that is not available in prior art devices.
Waveguide
The microwaves produced by the cavity magnetron are guided into the oven by a waveguide. The waveguide is what allows the microwaves to be confined within a specific path and not allowed to travel in all directions, which could damage the magnetron or anybody that is nearby.
The waveguide is usually circular, although there are other types such as rectangular or two-dimensional slabs. The shape of the guide determines its capability to transmit EM waves. For example, a rectangular guide cannot conduct a wave of a different shape.
Magnetron
The magnetron generates microwave radiation that heats the food in the oven. It consists of a cylindrical diode working as a cathode with an anode around it, with a series of coupled resounding cavities (see the figure).
A high DC voltage, up to 4,000 volts, causes electrons to flow through the vacuum from the hot negative cathode in the center to the positive anode surrounding it. An axial magnetic field (produced by the poles of two horseshoe-shaped alnico magnets) forces the electrons to rotate and pass through slots in the anode.
As they rotate, the electrons are swept back and forth by the magnetic field, creating an oscillation that generates microwave energy. This is the same mechanism that makes a transistor work, but without the need for electrostatic control using a control grid, which is more complicated and expensive.
Ohmmeter
If your microwave oven stops producing heat, the magnetron may have a problem. It's a complicated component that can be expensive to replace, but there are a few ways to diagnose the problem. One way is to use a multimeter. Another is to track the temperature of water inside the microwave. These tests should be done only by experienced technicians or electricians.
First, you should unplug the microwave and make sure that the high voltage transformer is disconnected from the power supply. Then, set the ohmmeter to its highest resistance scale. Touch one of the meter's probes to the magnetron terminal and the other to the metal magnetron housing. The ohmmeter should read infinite, so any other reading indicates an open circuit. It's important to note that the magnetron can give you a severe electrical shock, even if it is unplugged and discharged. That's why you should always wear gloves when handling it. You should also keep in mind that the microwave can still produce a small amount of current when the magnetron is defective.
