Switching power supply output part circuit diagram

The 12V voltage is unstable. You should check the output part of the switching power supply first , as shown in the figure. Check that the secondary winding of the switching transformer and VD4 are normal, and that the inductor L2 has no weak soldering. The parameters of filter capacitors C22 and C23 are both 1000pF/16V. Use a capacitance meter to measure C23. It is basically normal (the capacity drops slightly), but the capacity of C22 drops to less than 80μF. The reason for comparing C22 and C23 is that the main power supply of the machine Installed in the base of the monitor, the space is very small and the heat dissipation is poor. C22 and C23 are both close to the 12V rectifier diode (especially C22 is closer). After being baked, the capacity decreases, making the 12V load capacity worse, and thus This failure occurs. Although 5V and 3.3V originate from 12V, the instability of 12V does not drop below the limit supply voltage of the 5V and 3.3V converters , so these two voltages remain normal, thus masking the nature of the fault.