Switching power supply fault repair step

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Summary:

First, preparation work

Prepare a simple test socket with protection, as shown in Figure 1. Its role is to prevent circuit fire caused by the breakdown of the switch tube and quickly determine the fault range.

Second, the switching power supply common fault repair steps

The block diagram of the switching power supply is shown in Figure 2.

1. At the moment of power-on, after the bulb flashes, it gradually goes out, then the power supply is normal from input to rectification and filtering, and the fault should be in the back circuit. Otherwise the power fuse or the input filter inductor is open.
2. If the rectification and filtering circuit is normal, it is detected whether there is 310V voltage across the switch tube. If not, the sampling resistor R0 or the transformer primary open circuit.
3. If the voltage of the switch tube is normal, it is detected whether the switch circuit of the switch tube has a voltage of several volts to ten volts, and if not, the start resistor and the drive circuit are detected.
4. If the drive has voltage and the switch is normal, the self-excited winding is faulty or the feedback circuit is faulty.
5. If the lamp is always on, the switch tube breaks down (short circuit) or the rectifier bridge breaks down (short circuit).
6. If the lamp is periodically lit, the load has a short-circuit fault and the load can be emphasized.
7. If the switch is replaced multiple times, the peak voltage elimination circuit and the load are detected to have an open circuit fault.
8. After the above maintenance steps and detecting that the load voltage is basically normal, the switch K can be closed, and if the output is normal when detecting again, the switching power supply has been repaired.
9. Note: The negative feedback circuit of the switching power supply and the secondary of the transformer must not be opened, otherwise it will damage other parts of the circuit.