What is the maintenance method of switching power supply?
1. Check the rectification and filtering circuit. If the fuse inside turns black and STR-F6454 (NQB21) explodes and is damaged, the rectification diodes VD801A~VD8O4A and surge absorption capacitors C805~C808 should be checked+ 300V filtering capacitor C810, peak absorption capacitors C811, C827 (some models do not have C827) R823,R824,UB822).
2. Check that the STR-F6454 (4) pin external circuit is the power supply terminal for starting the power supply, and the normal voltage is 18.2V. If the voltage of the pin is less than 11V and remains stable, check the electronic voltage regulator circuit with components such as V801, VD808 (18V), VD803 (22V) as the core; If there is a fluctuation between llV~l5V, it indicates that the switching power supply has started to vibrate. Then check whether there is a short circuit in the secondary rectification, filtering components, and load circuit of the switching transformer, especially in the row circuit.
3. Check the voltage regulation control loop. If the+B voltage gradually drops from 160V to zero at the moment of power on, then check the components of the voltage regulation control loop. You can replace the optocoupler N830 first, and then replace the error amplifier N831. It is best to check if R807 is open circuit.
Tip: A Schottky diode AKO3 is externally connected between pins (4) and (5) of this IC. During the actual repair, this diode can be omitted or replaced with RU2 RU4, 55295 and other types of diodes.
