1. Faulty component: high voltage diode breakdown

Fault phenomenon: high-voltage fuse blown or high-voltage bidirectional diode breakdown, there is a "buzzing" abnormal sound

High voltage transformer secondary coil current>400mA, high voltage transformer primary coil current is about 3A

No heating main circuit fuse blown

Failure analysis:

When the high-voltage diode is reversed breakdown, the circuit cannot play the role of voltage doubler, the magnetron cannot work, and the secondary circuit has only a high-voltage capacitive load. In the circuit of picture (a) (with high-voltage fuse, no bidirectional diode), the secondary current is about twice the normal working current, and the high-voltage fuse operates to prevent the high-voltage transformer from burning. In the circuit of Figure (b) (no high-voltage fuse, there is a bidirectional diode), the voltage applied to both ends of D2 (high-voltage diode) is greater than the reverse breakdown voltage of D2 (high-voltage diode), which breaks down D2 (high-voltage diode). It causes the transformer secondary to be directly disconnected within half a week, the main circuit fuse is blown, and the whole machine is powered off.

Judgment method: Use the high-end ohmmeter to measure the resistance between the two electrodes of the high-voltage diode, and the normal reading: the forward direction exceeds 10KΩ, and the reverse direction is infinite. Use an ohmmeter with a battery voltage higher than 9V. Abnormal reading: Continuity or infinity in both directions.

Or use a 500V megohmmeter to measure the resistance between the two electrodes. Normal reading: 0 ohm in the forward direction, infinity in the reverse direction; abnormal reading: both forward and reverse are on or both forward and reverse are infinite.

2. Fault component: high voltage bidirectional diode

Fault phenomenon: the main circuit fuse is blown

Fault analysis: When the high-voltage bidirectional diode breaks down, the secondary transformer is directly disconnected, the main circuit fuse is blown, and the whole machine is powered off.

Judgment method: Use the high-end ohmmeter to measure the resistance between the two electrodes of the high-voltage diode. Normal reading: infinity in both directions; abnormal reading: conduction in both directions or infinity in the other direction.

3, faulty parts: high-voltage capacitor open circuit or open circuit

Fault phenomenon: main circuit fuse blown, high voltage fuse blown, no heating

Fault analysis: When the high-voltage capacitor is short-circuited, it will cause a direct short circuit within half a week of the transformer secondary, and the main circuit fuse will blow or the high-voltage fuse will blow. When the high-voltage capacitor is disconnected, the secondary of the transformer is disconnected, and the magnetron cannot work.

Judgment method: Use the high-end ohmmeter to measure the resistance between the two electrodes of the high-voltage diode, and the normal reading: a few ohms are displayed instantly, and gradually return to about 100MΩ.

4, the faulty part: magnetron

Fault phenomenon: main circuit fuse blown, high voltage fuse blown, no heating

Fault analysis: When the magnetron insulation breakdown, the transformer secondary is directly short-circuited, and the main circuit fuse is blown or the high-voltage fuse is blown. When the filament of the magnetron is broken, the magnetron cannot work. There is also a situation where the vacuum of the magnetron die is insufficient, which may cause slow heating or no heating.

Judgment method: Detect the resistance between the two terminals of the magnetron with the R×1 file of the ohmmeter, and the normal reading: less than 1Ω, otherwise it will be damaged. Use a high-end ohmmeter to measure the resistance between the magnetron filament and the casing, or use a 500V megohmmeter to measure the insulation resistance, and the normal reading: infinity or above 00MΩ.

5. Fault component: high voltage transformer

Fault phenomenon: the main circuit fuse is blown, no heating.

Fault analysis: When the transformer insulation breaks down, the primary current of the transformer increases rapidly and the main circuit fuse blows. When the transformer coil is open. The magnetron does not work and the microwave oven does not heat up.

Judgment method: Detect the resistance between the primary coil, filament coil, and secondary coil with the R×1 file of the ohmmeter. Normal reading: a few ohms for the primary coil, less than 1 ohm for the filament coil, and a few hundred ohms for the secondary coil. Use a high-end ohmmeter to measure the resistance between the primary coil and the casing, and between the filament coil and the casing, and the normal reading: infinity.