AC Power Supply maintenance methods and actual combat experience
First, high-frequency AC Power Supply repair specific methods
1, AC Power Supply repair, we first need to use a multimeter to detect whether there is a breakdown of the power device breakdown, such as power rectifier bridge reactor, switch, high-frequency high-power rectifier, to suppress the inrush current high-power resistance And then need to re-test the output voltage port resistance is abnormal, such as the above device is damaged, we need to replace the new device.
(PFC) and pulse width modulation components (PWM), access to relevant information, familiar with the PFC and PWM modules each of the two, we will not be able to work properly after the completion of the above tests, and then we will test the power factor module (PFC) and pulse width modulation components (PWM) Feet of the function and the normal work of its modules necessary conditions.
3, for the PFC circuit with the need to measure the voltage at both ends of the filter capacitor is 380VDC or so, if 380VDC or so voltage, indicating that the PFC module is working properly, and then detect the working status of PWM components, measuring its power input VC, the reference voltage Output terminal VR, start control Vstart / Vcontrol terminal voltage is normal, the use of 220VAC / 220VAC isolation transformer to the AC Power Supply, with an oscilloscope to observe the PWM module CT end of the waveform is a good linear sawtooth or triangle, such as TL494 CT For the sawtooth wave, FA5310 its CT end for the triangular wave. Whether the waveform of the output terminal V0 is an ordered narrow pulse signal.
4, in the high-frequency AC Power Supply repair practice, there are many AC Power Supply using UC38 × × series 8-pin PWM components, most of the power can not work because the power supply resistance is damaged, or chip performance degradation. When there is no VC after the R circuit, PWM components can not work, need to replace the original power resistance with the same 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 GEDR 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 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, the external circuit connected with the VR terminal disconnect, VR from 0V to 5V, PWM components work properly, the output voltage is normal.
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, the field effect power switch G is very 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. V0 end with the board solder joints welded 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, high-frequency AC 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 high-frequency AC 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 AC Power Supply maintenance, Eliminate AC Power Supply failure, to achieve a multiplier effect.
Second, the exchange of power maintenance experience
1, AC Power Supply does not start when the vibration, we usually need to check the switching frequency is correct, the protection circuit is blocked, the voltage feedback circuit, the current feedback circuit and no problem, whether the breakdown of the switch. 2, AC Power Supply transformer heat or issued a sound, the general frequency is not switching. 3, high-frequency AC Power Supply output voltage power indicator flash is generally a short side of the secondary.