Switching power supply failure repair skills and frequent problem response
At present, switching power supply technology has been fully integrated into the design of various electronic products. However, with the expansion of the application area, the switching power supply begins to face various problems, and the damage problem is one of them. In this case, a technology is needed to repair the switching power supply, which is the switching power supply repair technology. Strictly speaking, the maintenance of switching power supply belongs to the category of chip-level maintenance, which plays a very important role in the field of industrial maintenance. This article will introduce some tips for switching power supply maintenance, and answer some common faults.
Repair Tips
The maintenance of switching power supply can be carried out in two ways, one is to observe when the power is off, and the other is to test with power on. In the event of a power failure, the cause of damage to the switching power supply can be determined by "seeing, smelling, asking, and measuring".
Power failure detection
Look: open the case of the power supply, check whether the fuse is blown, and then observe the internal conditions of the power supply. If you find 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.
Question: Ask about the process of power supply damage and whether the power supply has been operated in violation of regulations.
Measurement: before power is off, use a multimeter to measure the voltage across the high voltage capacitor. If the failure is caused by the switching power supply not oscillating or the switch tube being open, in most cases, the voltage at both ends of the high-voltage filter capacitor is not released, and the voltage is more than 300 volts, so be careful. Use a multimeter to measure the positive and negative resistance at both ends of the AC power line and the charging condition 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. Take off the load, and measure the ground resistance of each group of output terminals respectively. When normal, the needle should have a capacitor charge and discharge swing, and the last indication should be the resistance value of the discharge resistor of this circuit.
Power-on detection
After power on, you can judge whether there is any damage by observing the power supply, such as the fuse is burnt or the components are smoking. If necessary, 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, check the rectifier diode and filter capacitor. Measure the output of the secondary coil of the high-frequency transformer. If there is no output, focus on checking whether the switch tube is damaged, whether it is oscillating, whether the protection circuit is active, etc. If so, check the rectifier diode, filter capacitor, and three-way stabilizer pressure tube, etc.
If the power supply starts and then stops, the power supply is in the protection state. You can directly measure the voltage of the PWM chip protection input pin. If the voltage exceeds the specified value, it means that the power supply is in the protection state. You should focus on checking the cause of the protection.
Common malfunctions
blown fuse
If there is a blown fuse, there is a high possibility that it is caused by a problem with the circuit inside the power supply. Because the power supply works in the state of high voltage and high current, the fluctuation and surge of the grid voltage will cause the current in the power supply to increase instantaneously and cause the fuse to blow. The focus should be to check the rectifier diodes at the power input end, high-voltage filter electrolytic capacitors, inverter power switch tubes, etc., and check whether these components have breakdown, open circuit, damage, etc. If the fuse is indeed blown, you should first check the various components on the circuit board to see if the appearance of these components has been burnt or if the electrolyte has overflowed.
If there is no previous situation, then you need to use a multimeter to measure the switch tube to check whether the switch tube has a breakdown. Special attention should be paid to: When a certain component is damaged, it must not be turned on directly after replacement. It is very likely that the replaced component will be damaged because other high-voltage components are still faulty. It is necessary to conduct a comprehensive inspection and measurement of all high-voltage components in the above-mentioned circuit. Only then can the fault of blown fuse be completely ruled out.
