A few days ago, my friends sent me to use the Haihaixin LED39K300J LCD TV. The fault is gray screen (the gray screen is the backlight will be bright, no image). A friend of his peers said that he suspected the problem of the logic board, so he bought the logic board and changed the fault. Then disassemble the machine to start inspection, first check the Motherboard voltage points 12v, 5.1v 3.3v 1.8v are normal, check the logic board 12v supply voltage is also normal, directly check the VGH VGL voltage point is 0v.
Because the logic board peers have changed before, so I don't think about the logic board itself anymore. I suspect that there may be a problem with the screen or the screen board. The logic board of the machine is a double-row cable and the screen connection. Try to disconnect the logic first. A line between the board and the screen, and then test the voltage of the VGH foot to restore 25v, which can be judged that the screen board may be short-circuit protected.
[attach]525132[/attach][attach]525133[/attach]
Remove a screen cable VGH voltage is normal, the screen is also lit, the screen is like this
At this point, I can judge the problem of the screen board. I don’t have any experience in the screen maintenance board. I can only hold it and try it. I will open the screen in detail, and the components of the screen board are relatively small. Complex thinking, first check a few chip capacitors will leak, when the patch capacitor C20 is found, this capacitor is seriously leaking close to short circuit, remove the capacitor and then measure the leakage resistance of 20 or so ohms, the real fierce finally found Now, remove the capacitor, do not know how much capacity of this capacitor, so just remove a similar volume and replace the test machine, the long-lost blue screen came out and connected to the signal OKOK!
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