At present, switching power supply technology has been fully integrated into the design of various electronic products. However, with the expansion of the use surface, switching power supplies are beginning 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. This technology is the switching power supply maintenance technology. Strictly speaking, the maintenance of switching power supply belongs to the level of chip-level maintenance and has a very important position in the field of industrial maintenance. This article will introduce some of the techniques for switching power supply repair and answer some common faults.
Maintenance skills
The maintenance of the switching power supply can be carried out in two aspects, on the one hand, the observation in the case of power failure, and on the other hand, the power-on test. In the case of power failure, the cause of damage to the switching power supply can be determined by "looking, smelling, asking, and measuring".
Power failure detection
Look: Open the outer casing of the power supply, check if the fuse is blown, and then observe the internal condition of the power supply. If it is found that there is burnt or broken component on the PCB of the power supply, the components and related circuit components should be checked.
Smell: Smell the inside of the power supply for a smell, check for charred components.
Q: Ask if the power supply has been damaged and whether the power supply is operated in violation.
Quantity: Before powering up, use a multimeter to measure the voltage across the high voltage capacitor. If the switching power supply does not vibrate or the open circuit of the switch is faulty, in most cases, the voltage across the high-voltage filter capacitor is not bleed. This voltage is more than 300 volts, so be careful. Use a multimeter to measure the forward and reverse resistance and capacitor charging at both ends of the AC power line. 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. Disengage the load and measure the ground resistance of each group's output. When normal, the needle should have capacitor charging and discharging swing. The last indication should be the resistance of the bleeder resistor of the circuit.
Power-on detection
After power-on, you can observe the power supply to determine whether there is any damage, such as the burning of the fuse or the smoke of the components. If it is necessary to 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 there is no need to check the rectifier diode, filter capacitor, etc. Measure whether there is output of the secondary coil of the high-frequency transformer. If there is no key to check whether the switch is damaged, whether it is oscillating, whether the protection circuit is working, etc. If there is, it should focus on checking the rectifier diode, filter capacitor and three-way stability of each output side. Pressure tube and so on.
If the power supply is stopped, the power supply is in the protection state, and the voltage of the PWM chip protection input pin can be directly measured. If the voltage exceeds the specified value, the power supply is in the protection state, and the cause of the protection should be checked.
Common malfunctions
Fuse blown
In the event of a blown fuse, there is a high probability that it is caused by a problem with the wiring inside the power supply. Due to the high voltage and high current of the power supply, the fluctuations and surges of the power grid will cause the current in the power supply to increase instantaneously and the fuse will be blown. The key points should be to check the rectifier diode of the power input terminal, high-voltage filter electrolytic capacitor, inverter power switch tube, etc., check whether the component has breakdown, open circuit, damage, etc. If the fuse is really blown, you should first look at the various components on the board to see if the appearance of these components is burnt and there is no electrolyte spill.
If the previous situation does not occur, then you need to use a multimeter to measure the switch tube and check the switch tube for breakdown. It is necessary to pay special attention to: Do ​​not directly switch on a component when it is damaged. It is very likely that the other high-voltage components will still be damaged and the replacement components will be damaged. It is necessary to conduct a comprehensive inspection and measurement on all the high-voltage components of the above circuit. After that, the fuse blown fault can be completely eliminated.
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