1. When repairing the backlight source, you must master the characteristics of the backlight tube, light-emitting principle, as well as the composition and working principle of the backlight board. Although the appearance of the backlight board and component model composition is different, but the basic principle is the same. As long as there is a theoretical basis, you can analyze the fault. There are few types of backlight board failures, only 3-4 types. The backlight board's high-voltage output and power amplifier circuit principle is simple, mainly full-bridge / half-bridge drive, usually MOS tubes or power modules.

2. The backlight board maintenance must first ensure that the power supply works properly. That is, when the standby power supply is 3.3V or 5V, 12V, 24V and the PFC circuit is working properly, only when the backlight system can be overhauled.

3. Overhaul, you can remove the power supply board to the main board of the line, the standby voltage 5V respectively with STB (standby control), BRIl (dimming) and BL-ON (backlight control) of the three feet connected together. Under normal circumstances, the backlight board should be able to light up normally, then this step can determine whether the motherboard problem or power board problems.

4. If the backlight tube is still not lit, it means that there is no pulse signal applied to the backlight inverter. When repairing the backlight circuit, the backlight system can be considered as a line sweep circuit to overhaul.

5. The backlight control chip has a function. When the chip is first powered on, it is not controlled and protected by any feedback pins for about 2 seconds. It has an output pulse, after starting to get its normal feedback signal from the detection pins before it enters a normal working state. If there is no feedback signal or abnormal feedback signal after startup, the chip will enter the protection state and stop outputting the excitation signal.

6. The use of this feature first in the power up now detect the backlight control lC pulse output pin in the power up with or without voltage output, according to the voltage value to determine the point of failure is in the backlight control chip as the core of the circuit or in the post-level circuit.

7. If there is a signal output, it can be judged that the fault is in the rear drive part, otherwise the fault is in the backlight chip control part. We can measure whether there is an AC excitation signal output at the output of the post-stage excitation transformer. Because the operating frequency of the backlight circuit exceeds the frequency response of our ordinary multimeter, so there is no accurate voltage value. The digital meter is usually about 30 volts, and the mechanical meter is about 10 volts. It should be emphasized that regardless of the voltage value, the voltage value obtained by the two windings must be the same, otherwise there is a problem.

8. When the output pulse of the excitation transformer is normal, continue to measure step by step towards the back stage until the short circuit point of the pulse is found.