our methods of switching power supply maintenance
One is the short-circuit method, the second is the series bulb method, the third is the dummy load method, and the fourth is the replacement method.
1. Short circuit method
Most of the switching power supplies of liquid crystal displays use a direct sampling voltage regulator control circuit with a photoelectric combiner. When the output voltage is high, the short-circuit method can be used to distinguish the fault range.
2, series bulb method
The series bulb method means to remove the fuse of the input circuit and use a f 0W/220V bulb in series at both ends of the fuse. After the AC voltage is applied, if the light bulb is very bright, it means that the circuit has a short circuit. The light bulb has a certain degree of resistance, such as a 60W/220V light bulb, its resistance is about soon (referring to thermal resistance), and the light bulb plays a certain current limiting role.
One is that the failure of the circuit can be roughly judged by the brightness of the light bulb intuitively, and the other is that the current limiting effect of the light bulb will not immediately cause the circuit with a short circuit to burn out the components.
After removing the short circuit, the brightness of the bulb will dim, then remove the bulb and attach the fuse.
3. Dummy load method
When repairing the switching power supply, in order to judge whether it is the fault of the load circuit or the power supply itself, it is often necessary to disconnect the load, and add a dummy load to the output end of the switching power supply (usually 12V) to test the machine.
The reason for choosing to connect the dummy load is that the energy stored in the primary winding of the switching transformer will be released to the secondary during the period when the switching tube is turned off. damage.
Regarding the selection of dummy loads, generally choose 30-66W/12V bulbs (used in cars or motorcycles) as dummy loads. voltage level.
In order to reduce the starting current, a 30W electric soldering iron or a high-power 600Q-1kn resistor can also be used as a dummy load.
4. Substitution method
In the liquid crystal display switching power supply, a power control chip is generally used, and such power control chips are cheap.
Therefore, when it is estimated that there is a problem with the power control chip, the replacement method can be considered for replacement.
