Changhong UD42B6000iD LCD backlight is on the light to extinguish a troubleshooting example - android - Phones Developers

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Every year, when the rush to the autumn harvest or the harvest season, the business is really plummeting, and they are busy collecting crops, that is, there are things that are broken and no time to repair. During this time, I caught up with the autumn harvest, and the guy panicked. Sitting in the store doing nothing, come to God to pull an LCD TV, saying that the boot screen is off, the sound is normal, ask if you can repair, this year does not repair the LCD, you can repair? Answer: Yes. Moved down to see is a Changhong 42 LED LCD, or a 3D TV, model is UD42B6000iD, then the operating table on the LCD, boot really as the user said, the screen is on for one second, then the black screen, then the sound of the boot music. It seems that the backlight is not bad or the light bar is broken. There are very few bad things in this problem. Immediately quoted, repaired close to orange black brown, if the screen is broken, the user agrees, put down the TV to leave, the model and the whole machine block diagram are as follows:


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Firstly, the power supply board is tested for normal power supply. The main voltage and resistance of the backlight board are directly measured. The patch field tube breakdown of the Q50 is found. Check the periphery and find the field tube overcurrent detection. Two 6R2 and one 470. All the resistors were damaged. It was found that the over-current protection pin of the main chip of the model GB3000 blocked 3 ohms on the ground, short-circuited, and all the peripherals were short-circuited. It seems that the chip is also finished, and the repair has come to an end.


A few days later, the board was sent back, and the installation was still the same. The head was big. Is the backlight board bad? But I don't believe it. I still need to determine whether it is a problem with the newly-changed backlight board. If the voltage of the light bar is found, the voltage rises to about 40 volts and falls immediately. In order to distinguish whether the light bar is faulty or the backlight is faulty, the light bar is directly measured. The plug-in circuit and the light bar circuit have a total of eight paths, corresponding to eight field tubes respectively. The main chip GB3000 is used to control the conduction amount of the field tube, and the over-voltage is closed when the over-voltage and under-voltage are under pressure, which can protect the current and pass the current. Detect to precisely control the brightness of the lamp bead to make the brightness uniform.


At the instant of power-on, the test points of the eight loops were measured separately, and the voltage was found to be biased. The following six are about 3.8 volts when the screen is bright, and about 1.8 volts after the protection, but the top two are not normal, and the light reaches 30 volts when bright. Above, the backlight is not bright and there is a voltage of about 20 volts. Now it has been basically confirmed that the newly replaced board is no problem, and the lamp bead is estimated to be short-circuited. The backlight picture is as follows:




Contact the user to change the repair price, clear the risk details and the user, ask the user to agree to start the screen split, no more to say below, directly on the map











The fault point was found, it is obvious, but it is not easy to handle, see the picture below.






Two programs, first, change the seat. Second, the flying line. No matter how bad it is, I don’t think about changing the light bar and the cable. The screen has been removed. I don’t want to put it for a few more days. The risk will increase exponentially. Consider changing the seat and finding a suitable foot for the double column. 12-foot seat, use the air gun to heat the back to remove, remember, it is best not to heat the front, it is easy to burn the seat, the picture is as follows








This kind of seat is not too good to weld, but it is still successful, as shown below





The next step is to deal with the soft cable, cut the burnt cable neatly, and the two sides are too wide. To fix it, be sure to fix the two sides in parallel. Use a wallpaper knife to scrape the outer insulating paint. Be careful not to Too hard, the picture is shown below




There is a blue plastic mat at the plug of the original machine. In order to make the cable and the seat contact firmly, it has to be removed and attached to the back of the trimmed cable. This is simple, just plug it in. See the picture below.




The time to witness the miracle is coming, oh my mother, how is my heart thumping, the blood pressure is also high, the power is turned on, the lamp bead is perfectly lit, then it is not a dark joy, just laugh, look at the picture




Next, it was a screen that was shocked and stunned. Pay attention to the hand and don't be embarrassed. If you have to give up the test, the test machine is normal, and the picture is normal. Waiting for this picture, huh, huh





Thank you for watching, a little embarrassing, make it happen!


The whole process is assisted by my wife. I will say thank you to my beautiful wife.