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Common faults and judgment methods for high-voltage

Common faults and judgment methods for high-voltage

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[Abstract]:
The secondary coil current of the high voltage transformer is >400mA, and the primary coil current of the high voltage transformer is about 3A
1, faulty components: high voltage diode breakdown
Symptom: High-voltage fuse blows or high-voltage bidirectional diode breakdown, with a "ww" abnormal sound
The secondary coil current of the high voltage transformer is >400mA, and the primary coil current of the high voltage transformer is about 3A.
Unheated main circuit fuse blown
Failure analysis:
When the high-voltage diode reverses breakdown, the circuit cannot double the voltage, the magnetron cannot work, and the secondary circuit has only one high-voltage capacitive load. In the circuit of Figure (a) (with high-voltage fuse, no bidirectional diode), the secondary current is more than twice the normal operating current, and the high-voltage fuse operates to prevent the high-voltage transformer from burning. In the circuit of Figure (b) (without high-voltage fuses, with bidirectional diodes), the voltage across D2 (high-voltage diode) is greater than the reverse breakdown voltage of D2 (high-voltage diode), which breaks down D2 (high-voltage diode). The transformer is directly disconnected in the secondary half cycle, the main circuit fuse is blown, and the whole machine is powered off.
Judgment method: Measure the resistance between the two electrodes of the high-voltage diode with the highest level of the ohmmeter. The normal reading: forward exceeds 10KΩ, and the reverse direction is infinity. Use an ohmmeter with a battery voltage higher than 9V. Abnormal reading: On or in both directions are infinite.
Or use a 500V megger to measure the resistance between the two electrodes, normal reading: forward 0 ohms, reverse infinity; abnormal readings: both positive and negative conduction or positive and negative are infinite.
 
2, faulty parts: high voltage bidirectional diode
Symptom: 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: Measure the resistance between the two electrodes of the high voltage diode with the highest level of the ohmmeter. Normal reading: both directions are infinite; abnormal reading: both directions are conducting or one direction is conducting and the other direction is infinite.
 
3, faulty components: high voltage capacitor open or open circuit
Fault phenomenon: main circuit fuse is blown, high voltage fuse is blown, no heating
Fault analysis: When the high-voltage capacitor is short-circuited, it causes a direct short circuit in the secondary half-cycle of the transformer, and the main circuit fuse is blown or the high-voltage fuse is blown. When the high-voltage capacitor is broken, the secondary of the transformer is broken and the magnetron cannot work.
Judgment method: Measure the resistance between the two electrodes of the high-voltage diode with the highest level of the ohmmeter. Normal reading: display a few ohms in an instant, and gradually return to about 100MΩ.
 
4, faulty parts: magnetron
Fault phenomenon: main circuit fuse is blown, high voltage fuse is blown, no heating
Fault analysis: When the magnetron insulation breaks down, the transformer secondary is directly short-circuited, the main circuit fuse is blown or the high-voltage fuse is blown. When the magnetron filament is broken, the magnetron does not work. There is also a case where the magnetron core has insufficient vacuum and may cause slow or no heating.
Judgment method: Detect the resistance between the two terminals of the magnetron with the R×1 file of the ohmmeter. The normal reading: less than 1Ω, otherwise it will be damaged. Use the highest level of the ohmmeter to measure the resistance between the magnet filament and the case, or measure the insulation resistance with a 500V megger. Normal reading: infinity or above 00MΩ.
 
5, fault components: high voltage transformer
Symptom: The main circuit fuse is blown and not heated.
   Fault analysis: When the transformer insulation breakdown, the primary current of the transformer increases rapidly, and the main circuit fuse is blown. 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, the filament coil and the secondary coil with the R×1 file of the ohmmeter. Normal reading: several ohms of the primary coil, less than 1 ohm of the filament coil, and several hundred ohms of the secondary coil. Use the highest level of the ohmmeter to measure the resistance between the primary coil and the casing, between the filament coil and the casing, and the normal reading: infinity.
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