What are the repair methods of switching power supply and how to maintain the socket switch
In terms of troubleshooting methods for switching power supplies, I will tell you about them here.
1. When repairing the switching power supply, first use a multimeter to check whether each power component is broken down and short-circuited, the switching power supply shell such as the power rectifier bridge stack, the switching tube, the high-frequency high-power rectifier tube; whether the high-power resistor that suppresses the surge current is blown. Then check whether the resistance of each output voltage port is abnormal. If the above parts are damaged, they need to be replaced.
2. After the first step is completed, it still cannot work normally after turning on the power supply. Next, check the power factor module (PFC) and pulse width modulation module (PWM), consult relevant information, and be familiar with the function and function of each pin of the PFC and PWM module. A prerequisite for its modules to work properly.
3. Then, for the power supply with PFC circuit, it is necessary to measure whether the voltage at both ends of the filter capacitor is about 380VDC. If there is a voltage of about 380VDC, it means that the PFC module is working normally. Reference voltage output terminal VR, start to control whether the voltage of Vstart/Vcontrol terminal is normal, use 220VAC/220VAC isolation transformer to supply power to the switching power supply, and use an oscilloscope to observe whether the waveform of the CT terminal of the PWM module to ground is a sawtooth wave or triangle with good linearity, such as TL494 The CT terminal is a sawtooth wave, and the CT terminal of FA5310 is a triangular wave. Whether the waveform of the output terminal V0 is an ordered narrow pulse signal.
4. In the practice of switching power supply maintenance, many switching power supplies use UC38×× series 8-pin PWM components. Most power supplies of switching power supply adapters cannot work because the starting resistor of the power supply is damaged, or the performance of the chip is degraded. When R is disconnected and there is no VC, the PWM component cannot work, and it is necessary to replace the resistor with the same resistance value as the original power. When the starting current of the PWM component increases, the value of R can be reduced until the PWM component can work normally. When repairing a GE DR power supply, the PWM module is UC3843, and no other abnormalities were found in the inspection. After connecting a 220K resistor to R (220K), the PWM component works and the output voltage is normal. Sometimes due to peripheral circuit failure, the 5V voltage at the VR terminal is 0V, and the PWM component does not work. When repairing the power supply of the Kodak 8900 camera, when this happens, disconnect the external circuit connected to the VR terminal, and VR changes from 0V to 5V, the PWM component works normally, and the output voltage is normal.
5. When there is no voltage of about 380VDC on the filter capacitor, it means that the PFC circuit is not working normally. The key detection pins of the PFC module are the power input pin VC, the start pin Vstart/control, CT and RT pins and V0 pin. When repairing a Fuji 3000 camera, there is no 380VDC voltage on the filter capacitor on the test board. VC, Vstart/control, CT and RT waveforms and V0 waveforms are all normal, and there is no V0 waveform in the measurement field effect power switch G. Since FA5331 (PFC) is a chip component, there will be a virtual gap between the V0 terminal and the board after the machine has been used for a long time. Welding, the V0 signal is not sent to the G pole of the field effect tube. Solder the V0 terminal to the solder spot on the board, and use a multimeter to measure the voltage of the filter capacitor to 380VDC. When the Vstart/control terminal is low level, PFC cannot work either, and it is necessary to detect the relevant circuits whose terminals are connected with the periphery.
