A circuit diagram of a switching power supply

12V voltage instability, you should first check the switching power supply output section, as shown in FIG. The secondary winding of the
A circuit diagram of a switching power supply - schematic

transformer and the switch VD4 examination were normal, no inductor L2 Weld phenomenon. Filter capacitors C22 and C23 parameters are 1000pF / 16V, measuring capacitance meter C23, normal (capacity decreased slightly), but the C22 capacity has dropped to less than 80 F, the C22, C23 with the analysis of the reasons is the machine's main power mounted within the base of the monitor, the space is small, poor heat dissipation, and C22, C23 are close to 12V rectifier diode (especially C22 closer together), decreased capacity after being baked to make 12V with a load capacity deteriorates, and then this failure. Although derived from the 5V and 3.3V 12V, 12V instability but not down to 5V and 3.3V supply voltage converter limit or less, so the two voltages have been normal, and thus conceal the nature of the fault.

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