PCB plate of switch power supply service you understand?
1. The machine testing rectifier circuit PCB points D1 - D4 breakdown or open circuit, filter circuit of capacitance is damaged, balancing resistor R1, R2 is normal, step-down resistance R3 will burn out or resistance increase failure power (test).
2. Detection switch tube settlement b - e and c - e if there is a breakdown phenomenon of short circuit, measure each winding switching transformer short-circuit phenomenon, to make sure the switch tube, and the stand or fall of switching transformer power (test).
3. The detection of the secondary output winding rectifier filter element, see whether filter capacitance bulge, or is damaged, in order to rule out the possibility of secondary circuit short circuit.
4. The PCB plate detection absorption loop D5, R11, C9 is normal power (test).
5. PCB points under normal operation of machine in determining the above components, we can put down from the inverter switch power board separately carries on the electrical test.With voltage regulator slowly to switch power supply of rated voltage value, at this time should be able to hear when transformer vibration squeak, such as didn't hear the sound of the start up, using a multimeter to test whether UC3844 power level between positive and negative about 12 v - 16 v dc voltage.
6. After determining UC3844 voltage of the power supply is normal, can use the oscilloscope check UC3844 6 feet for PWM wave output to the trigger the end of the switch tube (according to different circuit design, the frequency of PWM wave between 20 KHZ to 100 KHZ)