1, the fuse tube is blown: carefully check the various components on the circuit board to see whether the appearance of these components is burned or there is electrolyte overflow, smell - smell no odor; Then measure the resistance value of the power input to see the local short-circuit phenomenon; Then measure whether the power filter capacitor can be charged and discharged normally, whether the switching power tube is broken down and damaged, whether the UC3842 and the surrounding components are broken, burned, etc., if the components are damaged, you can replace them.
2, no DC voltage output or voltage output instability: First of all, use a multimeter to measure whether the various components of the high-frequency pulse transformer are damaged, excluding the high-frequency rectifier diode breakdown, load short circuit; Then measure the DC voltage of each output to see if the control circuit of the power supply is faulty; Then use a multimeter to statically measure whether the rectifier diode and low-voltage filter capacitor in the high-frequency filter circuit are damaged. If the above components are damaged, replace the new components to eliminate them.
3, no DC voltage output, but the safety wire is intact: First judge whether the charger's change control chip UC3842 is in the king state or has been damaged. If these feet are not broken down, and the charger still cannot start normally, it also indicates that the UC3842 has been damaged and should be replaced directly.