Special component 2

Question 3. how to detect and replace the magnetron?
( 1 ) The magnetron detects the high voltage leads on the filament terminal of the magnetron, and uses the multimeter to measure the cold resistance of the filament, normal is less than 19 ( usually tens of megohm ); rX10k2 is used to measure the resistance between the filament and the tube, and the normal is infinite. The big filament resistance is the common reason for the low output power of the magnetron. If the filament resistance is measured, it is not easy to judge that the magnetron has been damaged or has aged. Practice shows that most of this situation is the contact resistance formed by the oxidation accumulation of the magnetron filament pin or the socket; there are also errors caused by measurement, usually caused by the contact resistance between the meter and the measuring point, or the contact resistance between the stylus and the socket, and the problem of the magnetron itself is relatively rare, this kind of failure can happen only if the service life has passed, the long-term overload work or a few magnetron tubes with quality defects exist. So when testing, should be the magnetron foot sanding or scraping, remove dirt and oxide, and then measure, if the measurement resistance is still large, you can judge the magnetron bad. The name of the filament is that the magnetron itself is damaged and needs to be replaced. A small number of magnetron filament open-circuit is due to lead welding, the filament base can be prised open, with wire pliers to clamp the lead and the connecting piece, then the soldering iron can be welded firmly. In addition, when using various types of microwave equipment, you should choose the right place to put it on a solid workbench to prevent falling. Microwave equipment should be located away from TV and gas stoves.

Ask 4. What is the high voltage power transformer in the microwave oven?
High voltage transformer is a special magnetic leakage transformer. Its overall structure is shown in Figure 16-3. The internal wiring is shown in figure 16-4. It can be seen from the diagram that the high voltage transformer usually has 3 windings, one winding, the AC 220V city electric voltage applied in this winding, the secondary magnetron filament winding output communication 3. 3V of the filament voltage, the two high voltage winding output AC 2100V high pressure, and some fourth windings, that is the power adjustment winding. A plurality of silicon steel sheets with a certain thickness are inserted between one and two windings to form a magnetic shunt with high reluctance gap in the transformer. When the high voltage transformer works, a certain amount of leakage flux will be produced in the magnetic shunt circuit, which controls the output current of the transformer and keeps the working current of the magnetron relatively stable.
When magnetron operates, there is oscillating current in the two side high voltage winding of the transformer, resulting in magnetic saturation of the iron core nearby. Assuming that the magnetron's anode voltage rises and the anode current increases because of the city's electric wave action, the current of the two side windings of the transformer increases, making the magnetic saturation deepened and the leakage flux increasing, which makes the two side high voltage of the transformer down, that is, the anode voltage of the magnetron is reduced, the anode current falls, and vice versa. Therefore, it can automatically adjust the anode voltage and current and stabilize the output power of the microwave.
High voltage transformers mainly rely on leakage flux to keep the magnetron working current stable, so it is also known as magnetic flux leakage transformer. This transformer can maintain the stability of the magnetron anode current under the wide fluctuation range of the power supply, and has been widely applied in the microwave oven. In addition to special products, almost all microwave ovens use such transformers.

This article is from ALLICDATA ELECTRONICS　LIMITED.