1, the maintenance of backlight light bulb to grasp the characteristics, lighting principle and the composition of the back plate, working principle. Although the shape of the backlight, components and model composition are different, but the basic principle is the same, as long as there is a theoretical basis, you can analyze the fault, the type of back plate is rarely 3-4, the high voltage output and power amplification circuit of the backlight is simple, using the whole bridge/half bridge drive, generally using MOS tube or power module.
2, the overhaul of the backlight to ensure that the power supply part of the normal operation. That is, standby power supply 3.3V or $unit, PFC Circuit works properly, can overhaul the backlight system overhaul
3, overhaul can remove the power supply board to the motherboard line, the standby voltage 5V respectively with the STB (standby control) BRI (dimming) and bl-on (backlight control) 3 feet connected to the normal backlight should be able to light, this step can determine whether the motherboard problem or the power supply board.
4, if the backlight lamp still does not show that the pulse signal is not added to the backlight inverter. The backlight system can be viewed as a scanning circuit to overhaul the back photoelectric path
5, the backlight control chip has a characteristic, in the chip just on the power 2 seconds or so is not under any feedback pin control protection, is the output pulse, after starting to get its detection pin normal feedback signal will enter the normal working state. If no feedback signal or abnormal feedback signal is received after startup, the chip will enter the protection state to stop the output excitation signal.
6, the use of this feature first in the power to detect the backlight control IC pulse output of the foot on the power when there is no voltage output, the condition can be used to measure the pulse output of the signal waveform of the foot, can also be used to measure the AC voltage of the multimeter output pulse.
According to the voltage value here we determine whether the fault point is in the backlight control chip as the core of the circuit or in the back-level circuit. (need to pay attention to chip protection after the need to power off before starting to have 2 seconds output)
7, if there is a signal output, you can determine the fault in the rear-level driving part.
Otherwise the fault is in the backlight chip control section.
We can measure the subsequent level of excitation transformer output end whether there is AC excitation signal output (because the operating frequency of the backlight circuit in the 56KHZ or so beyond the frequency response of our ordinary multimeter so there is no accurate voltage value, the digital table is generally items volts around, mechanical table in the ~ volt around. It is important to stress that no matter how much the voltage value of 2 windings to obtain the voltage value must be the same, otherwise there is a problem.
8, when its excitation transformer output pulse normal, we will continue to step backward steps to measure until the short-circuit point of the pulse is found.
The maintenance process is a fast and effective overhaul method for the backlight circuit after the boot.