Several repair steps for switching power supplies are listed below:
1, test the rectifier circuit D1-D4 whether breakdown or broken filter circuit capacitor is damaged, balance resistor R1, R2 is normal, buck resistor R3 whether burnt or resistance value increase failure (test under power failure).
2, test the switching tube b-e junction, c-e junction whether there is a breakdown of short-circuit phenomenon, measuring the switching transformer winding whether there is a short-circuit phenomenon, in order to determine the switching tube, and the switching transformer is good or bad (test under power failure).
3, test the secondary output winding rectifier filter components, focus on whether the filter capacitor bulging or damaged, in order to exclude the possibility of secondary circuit short circuit.
4, test the absorption circuit D5, R11, C9 is normal (test under power failure).
5, in the case of determining the above components are normal, we can remove the switching power supply board from the inverter to power up the test alone. With the regulator slowly adjusted to the rated voltage value of the switching power supply, at this time should be able to hear the transformer vibration squeak, such as not heard the sound of vibration, use a multimeter to detect the power supply of the UC3844 positive, negative level between whether there is a DC voltage of 12V-16V or so.
6, in determining the UC3844 power supply voltage is normal, an oscilloscope can be used to see whether the UC3844 6 feet of PWM wave output to the trigger side of the switch (according to the different circuit design, the frequency of the PWM wave is generally between 20KHZ-100KHZ).
7, if there is no PWM wave output, then replace the timing components C5, R8, C6 or UC3844. after the above steps of elimination, the switching power supply should work normally. In the inverter, there are many types of switching power supply, but the basic principles are the same, for example, each PWM management chip has a power supply, timing components RC network, output PWM wave port, etc., as long as we understand their working principle, in accordance with certain methods and steps are able to troubleshoot.
