Several maintenance tips for switching power supplies
The maintenance of switching power supplies can be divided into two steps:
When the power is off, "look, smell, ask, and measure"
Look: Open the power supply shell, check whether the fuse is blown, and then observe the internal situation of the power supply. If you find that there are burnt parts or broken components on the PCB board of the power supply, you should focus on checking the components and related circuit components here.
Smell: Smell whether there is a burnt smell inside the power supply, and check whether there are burnt components.
Ask: Ask about the damage of the power supply and whether the power supply is operated illegally.
Measure: Before powering on, use a multimeter to measure the voltage across the high-voltage capacitor. If the fault is caused by the switching power supply not oscillating or the switch tube is open, in most cases, the voltage across the high-voltage filter capacitor is not discharged. This voltage is more than 300 volts, so be careful. Use a multimeter to measure the forward and reverse resistance at both ends of the AC power line and the charging of the capacitor. The resistance value should not be too low, otherwise there may be a short circuit inside the power supply. The capacitor should be able to charge and discharge. Disconnect the load and measure the ground resistance of each group of output terminals. Under normal circumstances, the needle should swing when the capacitor is charged and discharged, and the final indication should be the resistance value of the discharge resistor of this circuit.
Power-on detection
After powering on, observe whether the power supply has burned fuses and individual components are smoking. If so, cut off the power supply in time for maintenance.
Measure whether there is a 300-volt output at both ends of the high-voltage filter capacitor. If not, focus on checking the rectifier diode, filter capacitor, etc.
Measure whether there is output at the secondary coil of the high-frequency transformer. If not, focus on checking whether the switch tube is damaged, whether it is oscillating, whether the protection circuit is working, etc. If so, focus on checking the rectifier diode, filter capacitor, three-way voltage regulator tube, etc. on each output side.
If the power supply starts and stops, the power supply is in the protection state. The voltage of the protection input pin of the PWM chip can be directly measured. If the voltage exceeds the specified value, it means that the power supply is in the protection state, and the cause of the protection should be checked.
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