Switching power supply maintenance methods can be divided into several steps
5, when the filter capacitor no 380VDC voltage, indicating that the PFC circuit is not working properly, PFC module key detection pin for the power input pin VC, start the foot Vstart / control, CT and RT feet and V0 feet. When repairing a Fuji 3000 camera, test an on-board filter capacitor without 380VDC voltage. VC, Vstart / control, CT and RT waveforms and V0 waveforms are normal, measuring field effect power switch G very no V0 waveform, because FA5331 (PFC) for the patch components, the machine appears after a long time between the V0 and the board between the virtual Welding, V0 signal is not sent to the field effect transistor G pole. The V0 end with the board solder joint welding, with a multimeter to measure the filter capacitor has 380VDC voltage. When the Vstart / control side is low, PFC can not work, you have to check the end of the connection with the external circuit.
In short, the switching power supply circuit is easy and difficult, the power is very small, the output voltage varied. As long as the core of things to grasp, that is fully familiar with the basic structure of the switching power supply and the characteristics of PFC and PWM modules, the basic conditions of their work, in accordance with the above steps and methods, multi-hands maintenance of switching power supply, you can quickly remove the switch Power failure, to achieve a multiplier effect.
4, in the switching power supply repair practice, there are many switching power supply using UC38 × × series 8 feet PWM components, most of the power can not work because the power supply is damaged, or chip performance degradation. Starting current increases due to start circuit as shown below.
When there is no VC after the open circuit, PWM components can not work, need to replace the same power resistance with the original resistance. When the PWM component starts to increase the current, you can reduce the R value to the PWM component can work properly. In the repair of a GE DR power supply, the PWM module for the UC3843, detection found no other anomalies, R (220K) and then a 220K resistor, PWM components work, the output voltage is normal. Sometimes due to the external circuit failure, resulting in the VR terminal 5V voltage is 0V, PWM components do not work, in the repair Kodak 8900 camera power supply, encountered this situation, connected with the VR side of the external circuit, VR from 0V to 5V, PWM components work properly, the output voltage is normal.
3, then, for the PFC circuit with the power supply is required to measure the voltage at both ends of the filter capacitor is about 380VDC, if 380VDC voltage, indicating that the PFC module is working properly, and then detect the working status of PWM components to measure its power input VC, Reference voltage output VR, start control Vstart / Vcontrol terminal voltage is normal, the use of 220VAC / 220VAC isolation transformer to the switching power supply, with the oscilloscope to observe the PWM module CT end to ground waveform is linear good sawtooth or triangle, such as TL494 CT side for the sawtooth wave, FA5310 its CT side for the triangular wave. Whether the waveform of the output terminal V0 is an ordered narrow pulse signal.
?2, the first step is completed, after the power is not working properly, and then to detect the power factor module (PFC) and pulse width modulation components (PWM), access to relevant information, familiar with the PFC and PWM module each foot function and Its modules work properly prerequisites.
1, repair switching power supply, first with a multimeter to detect whether the power components breakdown short circuit, such as power rectifier bridge reactor, switch, high-frequency high-power rectifier; suppression of inrush current high-power resistance is blown. And then check the output voltage port resistance is abnormal, the above parts need to be replaced if damaged.
