How to Repair Computer Monitor Switching Power Supply
Connect the power plug of the display to an AC voltage regulator, then adjust the output voltage of the voltage regulator to about 100V, then power on for maintenance, and gradually increase the power supply voltage for maintenance.
Fault example 1: The fuse is burned out when the machine is turned on, and the output voltage is zero. This situation is generally caused by the breakdown of the switch tube and the short circuit between the emitter and collector. At this time, the switch tube can be removed first, and the resistance of the emitter and collector to ground can be measured. If it is zero or very small, it can be replaced. But it is also necessary to check whether there are any problems with other components before starting the machine.
Fault example 2: The grating is distorted in an "S" shape. This kind of problem should focus on checking the filter circuit and the voltage regulator circuit. Generally, it is because a diode is broken, and the full-wave rectification becomes half-wave rectification. This may also be caused by the reduction of the filter capacitor capacity.
Fault example 3: The AC 220V rectifier and filter circuit has a short-circuit fault, and the fuse is burned when it is turned on. First check whether the rectifier diode is short-circuited and whether the filter capacitor is seriously leaking. You can also unplug the degaussing coil, check whether the degaussing thermistor has a short-circuit fault, and replace it with a new one if so.
Fault example 4: There is no grating, no display, and the power indicator light is off, but the fuse is not burned. At this time, check whether the AC mutual inductance transformer is open circuit, whether the current limiting resistor of the rectifier circuit is open circuit (burned out) fails, or whether the rectifier diode is open circuit.
Fault example 5: There is no grating, no display, and there is an abnormal sound inside the machine. If there is a "squeak" sound, it means that the oscillation frequency is low, and the components related to the oscillation should be checked. If there is a "click" sound, it means that the power supply is over-current protected, and the over-current protection circuit should be checked.
Fault example six: The output voltage is higher or lower than the normal value. The output voltage is more than ten volts to tens of volts higher or lower than the normal value, but it is not zero, and the protection circuit has not acted. At this time, the fault phenomenon will vary with the voltage change. You can adjust the voltage regulator potentiometer. If the output remains unchanged or changes very little, it means that the sampling differential amplifier circuit is faulty, and the voltage regulator diode that provides the reference is broken down or There is a high chance of a short circuit.
