The microwave oven is not as complicated as it looks. The technology has been around since world war two. The first thing is safety. The high voltage capacitor in a microwave will stay charged long after the unit is unplugged. This capacitor can cause serious harm to you and your test equipment. If you do not understand the discharge procedure listed below, then please do not remove the cover. When you remove the cover the very first thing you do is discharge the capacitor.
High Voltage Capacitor and Diode Rectifier
Discharging procedure: For the high voltage capacitor in a microwave , use a 100 K ohm 25 W (or larger resistor with a clip lead to the metal chassis. You don't want the high voltage arcing across the terminals of the resistor. Clip the ground wire to an unpainted spot on the metal chassis. Use the discharge probe on each side of the capacitor in turn for a second or two. Then, confirm with a screwdriver (with a good insulated handle) across the capacitor terminals. If there is a big spark, you will know that it did not work, but at least there will now be no danger. DO NOT use a volt-ohm meter for this. If your discharging did not work, you may fry everything, including yourself.
Fuse
If the microwave is plugged into a known working plug, and the unit does nothing. The fuse may be blown. You will have to remove the cover to check and or replace the fuse. Fuses can blow from long runtimes or being run with a metal object in the microwave. If the fuse keeps blowing there is another problem. Do not replace the fuse more than once. There could be a possible short in the unit causing it.
Cabinet Interior
To get the high voltage needed for the magnetron to work the incoming power is passed through the capacitor, the diode rectifier, and the transformer. The capacitor pushes the voltage up higher. The diode rectifier is hooked to one terminal of the capacitor and the other end to the metal chassis. It rectifies the alternating current to direct current. If your microwave runs but does not heat, check the diode rectifier first. The transformer then increases the voltage even more. It is a step up transformer. Then the high voltage is sent to the magnetron.
Transformer
The magnetron is a electronic tube that uses a cathode, a anode, and an externally applied magnetic field to generate alternating currents at microwave frequencies. These microwaves are formed to the right length, width and thickness by the waveguide bridge. The waveguide bridge is used for directional transmission of the microwaves into the cooking chamber. Where they are moved around by the circulating fans. Till whatever is in the cooking chamber absorbs them.
Magnetron and Waveguide Bridge
