No DC voltage output

by:Mainbon     2021-07-10
If the fuse is intact, in the idle condition with load. The main reasons for this type of failure are: open circuit or short circuit in the over-voltage and over-current protection circuit; the vibration circuit does not work; the power supply is overloaded, and the high-frequency rectifier filter circuit The middle rectifier diode is broken down: leakage of the filter capacitor, etc. Maintenance method: First, use a multimeter to measure whether each component of the high-frequency pulse transformer is damaged: After eliminating the breakdown of the high-frequency rectifier diode and the load short-circuit, measure the DC voltage of each output terminal, if the output is still zero at this time , You can be sure that the control circuit of the power supply is faulty. 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 them with new ones, and the general fault can be eliminated . But pay attention: the output line is broken, open welding, and virtual welding can also cause this kind of failure. Pay attention to this situation when repairing.  No DC voltage output, but the fuse wire is intact  This phenomenon indicates that the charger is not working, or it has entered a protection state after working.  Maintenance method: Firstly, judge whether the charger's variable control chip UC3842 is in the state of working or has been damaged. The specific judgment method is: power on and measure the voltage of pin 7 of UC3842 to ground. If the voltage of pin 7 is normal and pin 8 has a voltage of +5∨, pins 1, 2, 4, and 6 will also have different voltages, indicating that the circuit has been activated. Vibration, UC3842 is basically normal. If the voltage of pin 7 is low and the other pins have no voltage, it means that UC3842 has been damaged. The most common damage is 7-foot-to-ground breakdown, 6, 7-foot-to-ground breakdown and 1, 7-foot-to-ground breakdown. If these pins are not broken down, and the charger still cannot start normally, it also shows that the UC3842 is damaged and should be replaced directly. If it is judged that the chip is not broken, check whether the current-limiting resistor of the gate of the switch is open welding, virtual welding or changing value, and whether the switching power tube itself has poor performance. In addition to this, a broken or poor contact of the power output line can also cause this failure, so you should also pay attention to it during maintenance.
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