Common reasons for the switching power supply with 3845 as the core to fail to vibrate: 1> If the voltage at both ends of the main power supply large filter capacitor (68u to 120u\/450V) is lower than 270V, replace the filter capacitor. < 2> Boot instantaneous 3845 7 pin whether there is 8, 5V or more voltage, not most of the starting resistance value is large. < 3> After starting up, the pin has a stable voltage of more than 12V, and there is no filter and current limiting resistance for the output power supply of the main transformer secondary winding. < 4> Measure whether 3843⑥ pin 2, 4V, no replacement 3843 chip and peripheral components.
Check whether the voltage of pin 6 at the power supply end is normal 16 volts, no or low voltage, and check the resistance value of the starting resistance