How to judge the quality of high-voltage capacitors?

1. Detection and judgment of non-energized conditions: Use a meter to measure the resistance. The resistance of both ends of the primary is 2 ohms, and the resistance of the secondary filament is close to short circuit. The resistance of the high-voltage winding is 80 to 120 ohms. The difference between different transformers is obvious.

2. Power-on detection and judgment: Connect the primary to 220V AC mains to see if the secondary voltage is within the range. The filament is about 4V and the high voltage is 2000V. The 2000V here is not easy to measure. The voltage measured by a common multimeter is not so high. Preliminary judgment may be made by leading the arc. This requires experience. It can also assist the judgment by measuring the no-load current. The transformer for microwave ovens controls the current to about 4A.

Check when the microwave oven is not working. First disconnect the connection of the transformer, and measure the resistance with a multimeter. The primary winding is about 2.2 ohms, and the high-voltage winding is about 130 ohms, which is normal. If one end of the high-voltage winding is connected to the ground, the resistance of the high-voltage winding should be measured. Connect one test lead to the bottom plate; connect the other test lead to the connection line with the high-voltage diode. The filament winding is too thick and too short, it is not easy to measure, and it is not often broken.

High-voltage transformers are valuable components as well as vulnerable components. It is very likely to occur: high-voltage line leakage, short-circuit, or burnout. We also discovered during repairs that the primary wire was actually made of aluminum-clad wire, and the solder joints with the inserts often had poor contact.

Detailed explanation of the quality of the detection capacitor

1. The measuring instrument needs to be set to the highest resistance range;

2. normal phenomenon:

a. Test the two terminals of the capacitor, it shows conduction in a short time (real jump), and then the resistance after charging is about 10MΩ;

b. The resistance between the terminal and the shell should be infinite;

3. Abnormal phenomenon:

a. The short-circuit capacitor is always on;

b. The open circuit capacitor always shows a resistance value of about 10MΩ due to its 10MΩ internal resistance;

c. When the internal wiring in the high-voltage capacitor is open, an infinite resistance will be displayed.

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