[This LCD TV was bought in 2013, the user said that the shutdown is good, then the backlight will not light up, the sound has been normal, the test machine is really like this, the boot screen has no reaction at all, the model number is shown below Pc Material,Pc Plastic Material,Pc Clear Material,Pc Material Properties WENZHOU TENGCAI ELECTRIC CO.,LTD , https://www.tengcaielectric.com
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When I opened the back cover, I found that there were two fewer screws. It seems to be a rework machine. The user also answered the truth. After the sale, I saw that I had to change the board, orange black and brown. The user didn’t want to change the board. , don't do it. Just pull the TV here, the power board is as shown below
The main circuit on the back of the power board is as shown below
Start test 12 volts 24 volts 5 volts normal, open standby voltage 3 volts normal, brightness control 1.3 volts is also normal, but the backlight voltage is only about 24 volts, indicating that the backlight circuit has problems, the secondary backlight chip model is OZ9967GN, measuring backlight chip power supply 12 Normal volts, backlight switching voltage and brightness control voltage are also added to the chip, but the boost triode driving voltage is 0 volts, the measured boost triode and boost diode are normal, the next step is to check the backlight protection and voltage detection The measured 10-pin low-voltage protection terminal of the chip is 1.7 volts normal, and the measured light bar over-voltage protection 4 feet is 0.1 volts, indicating that it is fine. The light bar open-circuit protection terminal 3 is 0.7 volts is normal, it seems that the chip is bad. The chances are great, but still not assured, because the goods are out of stock, in case of misjudgment, it will waste a few days, so continue to find a breakthrough.
Suddenly I think that many of the current chips have a reference voltage forming pin. It is not unfamiliar to many maintenance workers for the reference voltage. It is to generate a voltage inside the chip for the internal unit circuit of the chip, so I immediately find the data and find the OZ9967GN. 14 feet is the reference voltage forming and output pin, the voltage is 5 volts, not only for the internal use of the chip, but also directly output 5 volts for the external circuit of the chip to pull up, immediately test the chip 14 pin voltage, found to be 1.5 volts, abnormal Can not help but a happy heart, the fault point finally found is the backlight is not normal caused by the backlight is not bright, measured 14 feet to ground resistance is about 200 euros, not normal, remove the peripheral RC and then measure 200 euros, directly blow off The chip, the peripheral resistance returns to normal, and the chip reference voltage is determined to form an internal short circuit of the pin. Picture is as follows
I bought the chip on the chip, the blue screen appeared, the signal test machine was plugged in, everything was normal, troubleshooting
LCD TV accessories are not easy to buy, generally on the TB, if the judgment is wrong, it is a waste of time for labor and labor, so in the repair of the LCD to judge the chip failure must be cautious, if the chip is not commonly used, if you buy it back, if you judge the error, The next time I use it, I have to wait until the Year of the Monkey.
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