What are the Methods of Switching Power Supply Failure Inspection and Repair?

What are the maintenance steps of switching power supply?

Power-on detection. After power on, observe whether the power switch has burnt insurance and smoke from individual components. If so, cut off the power supply for maintenance.

Measure whether there is output from the secondary coil of the high-frequency transformer. If not, check whether the on off socket switch tube is damaged, whether it starts to vibrate, whether the protection circuit breaker panel board is active, etc., if there is, check the rectifier diode, filter capacitor, and three-way extension socket stability on each output side.

Check the volume after power off. Open the housing of the power supply, check whether the main fuse board with switches is blown, and then observe the internal situation of the power supply. If you find that there is a burnt or broken component on the PCB of the power supply, you should focus on the components and related circuit components here. Before powering on, use a multimeter to measure the voltage across the high-voltage capacitor. If the switching power supply fails to vibrate, in most cases, the voltage across the high-voltage filter capacitor is not discharged. Use a multimeter to measure the forward and reverse resistance of the AC power cord and the charging of the capacitor. Disconnect the load and measure the resistance to ground of each group of output terminals. When it is normal, there should be a capacitor charging and discharging swing on the needle.

What are the repair methods of the common troubleshooting of switching power supply ?

Fuse blown. Under normal circumstances, the blown fuse distribution box indicates that the internal circuit of the switching power supply has a short circuit or an overcurrent fault. As the switching power supply works under high voltage and high current conditions, the DC filter and conversion oscillation circuit works too long in the high voltage state, and the voltage changes relatively large. Fluctuations in grid voltage and surges will cause the current in the switch power supply to increase instantaneously and cause the distribution fuse board to blow. The focus should be to check the rectifier diode, high-voltage filter electrolytic capacitor, switching power tube, UC3842 itself and peripheral components at the input end of the power supply.

Repair method: Firstly, carefully check the various components on the circuit home distribution board to see if there is any burnt on the surface of these components, if there is any electrolyte overflow, and smell for any peculiar smell. After reading and smelling, check it with a multimeter. Second, measure the resistance value of the power input terminal. If it is less than 200K, it means that there is a partial short circuit phenomenon at the back end. Then measure the resistance values of the four rectifier diodes forward and reverse resistance and two current limiting resistors to see if there is a short circuit or burn out; then measure whether the power filter capacitor can be charged and discharged normally, and then measure whether the switching power tube is broken down. One point that needs to be explained is: because it is measured on the road, it may make the measurement result wrong and cause misjudgment. Therefore, if necessary, the components can be welded down and then measured. If there is still no such situation, measure whether the input power line and output power line are short-circuited internally.

Poor power load capacity. Poor power load capacity is a common fault, which usually occurs in old-fashioned or long-working power supplies. The main reason is the aging of various components, unstable operation of the switch tube, and failure to conduct heat dissipation in time.

Repair method: Use a multimeter to check the Zener diode, high-voltage filter capacitor, current limiting resistor for deterioration, etc. Then carefully check all the solder joints on the circuit board for open soldering and virtual connections. Re-solder the unsoldered solder joints and replace the deteriorated components, and the general fault can be eliminated.