See fault 1: The fuse tube is blown
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1, first carefully check the various components on the circuit board to see whether the appearance of these components is burned or there is electrolyte overflow, smell - smell no odor;
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2, then measure the resistance value of the power input, if less than 200kΩ, it indicates that there is a local short circuit phenomenon at the back end, and then measure the positive and negative resistance value of the 4 rectifier diodes and the resistance value of the two current limiting resistors to see whether there is a short circuit or burned out;
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3. Finally, measure whether the power filter capacitor can be charged and discharged normally, whether the switching power tube is broken down or damaged, whether UC3842 and the surrounding components are broken down or burned out.
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Common fault two: No DC voltage output or voltage output is unstable
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1. First of all, use a multimeter to measure whether the various components of the high-frequency pulse transformer are damaged, and eliminate the breakdown of the high-frequency rectifier diode and the short-circuit of the load;
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2, then measure the DC voltage of each output, if the output is still zero, it can be sure that the control circuit of the power supply is faulty;
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3. Finally, use a multimeter to statically measure whether the rectifier diode and low-voltage filter capacitor in the high-frequency filter circuit are damaged. If the above components are damaged, replace the new components, and the general fault can be eliminated.
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Common fault 3: No DC voltage output, but the fuse is intact
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1, First of all, we should determine whether the charger's change control chip UC3842 is in the king state or has been damaged. Pins 2, 4 and 6 will also have different voltages, indicating that the circuit has been activated and the UC3842 is basically normal. If pin 7 has low voltage and other pins have no voltage, it indicates that the UC3842 is damaged.
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2, if these feet are not broken, and the charger still can not start normally, it also indicates that the UC3842 has been damaged, should be replaced directly.
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Common fault four: The cooling fan does not turn
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1, first of all, use a multimeter to measure whether the control fan of the transistor is damaged, if the tube is not damaged, it may be the fan itself is damaged, you can pull the fan off the circuit board, in addition to a 12V direct current (pay attention to the positive and negative electrode), see whether to rotate, but also see if there is no foreign matter stuck;
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2, if the swing of the fan wire, the fan will turn, it indicates that there is a broken wire or poor contact of the connector inside the wire;
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3, if it still does not rotate, the fan will be broken