SMT SMD Sensor Reed
SMT SMD Sensor Reed
1. When repairing the switching power supply, first use a multimeter to check whether the power components are short circuited.
Such as the power rectifier bridge reactor, switch, high-frequency high-power rectifier; suppression of high-power resistors inrush current is blown. Then check whether the output voltage of each output voltage is abnormal. If the above components are damaged, replace them.
2. After the first step is completed, after the power is turned on, it still cannot work normally, and then the power factor module (PFC) and the pulse width modulation component (PWM) are to be detected. Refer to the related materials and be familiar with the functions of each pin of the PFC and PWM module. The prerequisites for the normal operation of its modules.
3. Then, for a power supply with a PFC circuit, it is necessary to measure whether the voltage across the filter capacitor is about 380VDC. If there is a voltage of about 380VDC, it means that the PFC module is working normally. Then, the working status of the PWM component is detected and the power input terminal VC is measured. Reference voltage output VR, start control Vstart/Vcontrol terminal voltage is normal, use 220VAC/220VAC isolation transformer to power the switching power supply, use an oscilloscope to observe whether the PWM module CT end to the ground waveform is a good linear sawtooth wave or triangle, such as TL494 The CT end is a sawtooth wave, and the FA5310 has a triangular wave at its CT end. Whether the waveform of the output V0 is an orderly narrow pulse signal.
4, in the switching power supply repair practice, there are many switching power supply using UC38 × × series 8-pin PWM components, most of the power supply can not work because of the power supply start-up resistor is damaged, or chip performance decline. When the R circuit is disconnected without VC, the PWM module cannot work and the resistor with the same resistance as the original power must be replaced. When the startup current of the PWM component increases, the R value can be reduced until the PWM component can work normally. When repairing a GE DR power supply, the PWM module was UC3843. No abnormality was detected. After a 220K resistor was connected to R (220K), the PWM module worked and the output voltage was normal. Sometimes because of peripheral circuit breakdown, cause 5V voltage of VR end to be 0V, PWM component does not work too, when repair Kodak 8900 camera power source, meet this situation, disconnect the external circuit connected with VR end, VR changes from 0V 5V, PWM components work normally and the output voltage is normal.
5. When the filter capacitor has no voltage of about 380 VDC, it means that the PFC circuit is not working properly.
The key detection pins of PFC module are power input pin VC, start pin Vstart/control, CT and RT pin and V0 pin. When repairing a Fuji 3000 camera, there was no 380VDC voltage on the filter capacitor on the test board. VC, Vstart/control, CT and RT waveforms and V0 waveforms are all normal. The measured field-effect power switch G has no V0 waveform. Since the FA5331 (PFC) is a patch element, the machine will use virtual end between the V0 terminal and the board for a long time. Welding, V0 signal is not sent to the FET G pole. Solder the V0 terminal to the on-board solder joint. Measure the filter capacitor with a multimeter at 380VDC. When the Vstart/control terminal is at a low level, the PFC cannot work, and the related circuits whose terminals and peripherals are connected are detected.
In short, the switching power supply circuit is easy and difficult, the power is varied, and the output voltage is varied. As long as they grasp the core things, that is fully familiar with the basic structure of the switching power supply and the characteristics of the PFC and PWM modules, the basic conditions for their work, in accordance with the above steps and methods, more hands-on maintenance of switching power supply, can quickly eliminate the switch Power failure, to achieve a multiplier effect.