Under normal circumstances, the blown fuse that power supply is a problem with the internal wiring. Due to the power supply work in high voltage, large current state, the power grid voltage fluctuations, surge current in the power supply will cause instant increase and make the blown fuse. Focus should check the power supply at the input rectifier diode, high pressure filter electrolytic capacitor, the inverter power switch tube and so on, check that the component breakdown, open circuit, damage, etc. If it was blown fuse, should first check the circuit boards of each element, see the appearance of all these components have to be burned, is there any electrolyte overflow, if did not find the above situation, the switch tube with or without breakdown short circuit is measured with a multimeter. Need to pay special attention to is: not in found to a certain element of damage, replace directly after boot, this is likely due to the high pressure components are defective and will replace the element damage, must all high voltage to the circuit components to conduct a comprehensive inspection measure, can completely eliminate the malfunction of blown fuse. ,

2, no dc voltage output or the output voltage is not stable

If the fuse is intact, with the load cases, dc voltage no output at all levels. This situation is mainly due to the following reasons: short circuit fault, open circuit fault phenomenon occurring in a power supply, the overvoltage and overcurrent protection circuit malfunction, auxiliary power supply failure, oscillation circuit without work, the power load is overweight, high frequency rectification filter circuit in the rectifier diode is punctured, the filter capacitor leakage, etc. In secondary element is measured with a multimeter, ruled out high-frequency rectifier diode breakdown, load short circuit, if the output is zero at this moment, you can definitely is a fault in the power control circuit. If any part of the voltage output shows that the front-end circuit works well, failure in high-frequency rectifier filter circuit. High frequency filter circuit is mainly composed of rectifier diode and low pressure filter capacitor dc voltage output, including rectifier diode breakdown can make the circuit no voltage output, output filter capacitor leakage will cause the voltage instability of fault. Measured with a multimeter static corresponding components can check out the damaged components.

3, the power load capacity is poor

The power load capacity is a common fault, are generally appeared in the old or work long time power supply, the main reason is that the components ageing, switch tube is not stable, not in a timely manner heat dissipation, etc. Should check whether the zener diode is mainly fever leakage, rectifier diode damage, damage to the high pressure filter capacitance, etc.

B. attention switch power supply

1, select the matters should be paid attention to when switching power supply

1) choose the appropriate input voltage specifications.

2) select the appropriate power. In order to make the life of the power supply growth, can choose more than 30% of rated power output models.

3) considering load characteristic. If the load is motor, bulb or capacitive load, when boot instantaneous current is larger, should choose appropriate power so as not to overload. If the load is the motor should be considered when downtime when voltage flow backward.

4) in addition, still need to consider the power of the working environment temperature, and the presence of additional auxiliary cooling device, in high temperature power to deduction output. The ring temperature deduction curve of output power.

5) according to the application needs to choose the function:

Protection function: over voltage protection (OVP), over temperature protection (OTP), over load protection (OLP) and so on.

Application functions: signal function (normal power supply, power supply failure), remote control, telemetry, parallel, functions, etc.

Special features: power factor correction (PFC), constant power (UPS)

6) choose needed to comply with safety and electromagnetic compatibility (EMC) certification.

2, use the matters needing attention of switch power supply

1) using power supply, make sure the input and output voltage and the nominal value of the power supply used specifications;

2) before electricity, check whether the input and output leads connected correctly, so as not to damage the user equipment;

3) check whether the installation is firm, install screw and power panel devices with and without contact, to measure the insulation resistance of the shell and the input, output, so as to avoid electric shock;

4) to ensure the safety of using and reduce interference, please ensure that the grounding end and reliable grounding;

5) multiplexed output of general component is main, auxiliary power supply output, the main output characteristic is better than that of auxiliary output, typically output current of the output. In order to ensure the output load regulation and output dynamic indexes, such as general requirements each with at least 10% of the load. If use need not the main road, so it must add appropriate dummy load of the main road;

6) please note: the power frequent switch will affect its life;

7) the working environment and loading may also affect its life.

C. switching power supply maintenance skills

1, repairs and switch power supply, the first to use multimeter test for a breakdown short-circuit power components, switch power supply shell, such as power rectifier bridge pile, switch tube, high-frequency high power rectifier; Inhibition of surge current of high power resistance is burn out. To detect the output voltage port resistance is abnormal, the damage of the above parts need to change.

2, the first step is completed, after turning on the power supply can not work normally, then to detect the power factor module (PFC) and pulse width modulation (PWM) component, refer to related information, familiar with PFC and PWM module of each foot function and the essential condition of the normal work of the module.

3, then, with the power of the PFC circuit is measured on both ends of the filter capacitance voltage is 380 VDC or so, if you have 380 VDC voltage, PFC modules work normally, then detect the working state of the PWM module, measuring the power input end of VC, VR reference voltage output end, start the control voltage of the Vstart/Vcontrol is normal, using 220 vac / 220 vac isolation transformer to the switch power supply, using the oscilloscope observation PWM module whether the end of the waveform of CT for linear sawtooth wave and triangle, such as TL494 CT end sawtooth wave, FA5310 its CT for the triangular wave. Output terminal where V0 waveform is for orderly narrow pulse signal. Switching power supply maintenance methods and techniques

4, in the practice of the switch power supply, maintenance, there are a lot of switch power supply adopts the UC38 PWM component x series 8 foot, most power supply switch power adapter can not work because of damage, the starting resistance of power or chip performance degradation. When R break no VC, PWM component doesn't work, need to change the same as the original power resistance value of resistance. After the starting current PWM component increases, can reduce the R value to the PWM component can work normally. When repairing a GE DR power, PWM module as the UC3843, inspection found no other exceptions, on the R (220 k) and a 220 k resistor, PWM component work, the output voltage is normal. Sometimes because of the peripheral circuit fault that VR end 5 v voltage of 0 v, PWM component does not work, also in the kodak 8900 camera power supply, encounter this situation, the linked to VR side open circuit disconnect, VR from 0 v to 5 v, PWM module to work properly, the output voltage is normal. Switching power supply maintenance methods and techniques

5, when no 380 VDC filter capacitor voltage, PFC circuit is not normal work, switch power supply circuit schematic PFC modules for power input key to detect the feet of VC, start the foot Vstart/control, CT and RT feet and where V0 feet. Repair a Fuji 3000 camera, test a board on the filter capacitance on no 380 VDC voltage. VC, Vstart/control, CT and RT waveform and where V0 waveform were normal, measuring field effect extremely where V0 waveform, power switch tube G because FA5331 (PFC) for SMT components, where V0 after machine with long side between the plate and welding, where V0 signal not to field effect tube G. Where V0 end with plate spot welding is good, filter 380 VDC capacitor voltage is measured with a multimeter. For low electricity at ordinary times when Vstart/control end, PFC also does not work, is to detect the endpoint associated with peripheral connected to the circuit.

All in all, switching power supply circuit is easy to the difficult, power is small, the output voltage is varied. As long as grasp the core of things, that is, fully familiar with the basic structure of switch power supply and the characteristics of PFC and PWM module, the basic condition of their work, according to the above steps and methods, more hands on maintenance of switch power supply, can quickly eliminate switch power failure, the effect of get twice the result with half the effort.