Methods and techniques for the maintenance of switching power supplies
1, repair switching power supply, first of all, use a multimeter to detect whether the power components are short-circuit breakdown, switching power supply shell, such as power rectifier bridge stack, switching tubes, high-frequency high-power rectifier; inhibit the inrush current of the high-power resistor is not burned out. Then test the output voltage port resistance is abnormal, the above components need to be replaced if damaged.
2, after the completion of the first step, the power supply can not work properly, then to detect the power factor module (PFC) and pulse width modulation components (PWM), consult the relevant information, familiar with the function of each foot of the PFC and PWM module and its modules work properly the necessary conditions.
3, then, for the power supply with PFC circuit is required to measure the filter capacitor voltage is about 380VDC, such as about 380VDC voltage, indicating that the PFC module is working properly, and then detect the PWM components of the working state, measuring its power input VC, reference voltage output VR, start control Vstart/Vcontrol terminal voltage is normal, the use of 220VAC / 220VAC / 220VAC / 220VAC / 220VAC components (PWM). 220VAC/220VAC isolation transformer to the switching power supply, using an oscilloscope to observe the PWM module CT terminal to ground waveform is a good linear sawtooth wave or triangle, such as the TL494 CT terminal for the sawtooth wave, the FA5310 CT end of the triangle wave. Whether the waveform of output V0 is an ordered narrow pulse signal. Switching power supply maintenance methods and techniques
4, in the switching power supply repair practice, there are many switching power supply using UC38 × × series 8-pin PWM components, switching power adapter most of the power supply does not work because the power supply start-up resistor is damaged, or the chip performance degradation. When R breaks no VC, PWM components can not work, need to replace the resistor with the same value as the original power resistance. When the PWM component startup current increases, you can reduce the value of R until the PWM component can work normally. In the repair of a GE DR power supply, PWM module for the UC3843, testing did not find any other abnormalities in the R (220K) on the parallel connection of a 220K resistor, PWM components work, the output voltage are normal. Sometimes due to peripheral circuit failure, resulting in the VR terminal 5V voltage of 0V, PWM components do not work, in the repair of the Kodak 8900 camera power supply, encountered this situation, and the VR terminal connected to the external circuit is disconnected, the VR from 0V to 5V, PWM components work normally, the output voltage is normal. Switching power supply repair methods and techniques
5, when there is no voltage on the filter capacitor about 380VDC, indicating that the PFC circuit does not work properly, switching power supply circuit schematic PFC module key detection feet for the power input feet VC, start feet Vstart/control, CT and RT feet and V0 feet. Repair a Fuji 3000 camera, test a board on the filter capacitor without 380VDC voltage. vc, Vstart/control, CT and RT waveforms as well as V0 waveforms are normal, measuring the field effect power switching tube G-pole without V0 waveforms, due to the FA5331 (PFC) for the SMD components, the machine with a long time after the emergence of the V0 end of the board between the virtual weld, the V0 signal is not V0 signal is not sent to the G pole of the field effect tube. The V0 end and the board soldering points welded, using a multimeter to measure the filter capacitor has 380VDC voltage. When the Vstart/control terminal is low, the PFC can not work, it is necessary to detect its endpoints and the periphery connected to the relevant circuits.
