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wholesale earbuds, earbuds in bulk, earbuds custom, true wireless earbuds TOPNOTCH INTERNATIONAL GROUP LIMITED , https://www.itopnoobluetooth.com It was still transferred from the previous 28 years. Component-level maintenance is indeed difficult due to lack of data. At that time, the bargaining price was: orange black and brown repaired, and later felt that this fault is endless, it is difficult to judge whether there is a problem with the power board or the high voltage board. Therefore, there is a kind of desire to give up and not to think about it, and I have not studied it carefully. The reason why the backlight driver does not start is always found. Just the day before yesterday, the customer called again and asked me to try my best. I asked for a fare increase and eventually added it to the yellow-green brown. Looking at the motivation of the money, I spent a whole day yesterday and finally fixed the TV.
Symptom: There is no light and black screen when booting. The flashlight can be seen by the flashlight on the screen, and the backlight high voltage board is not working. The model of the two-in-one power supply board of this machine is: BN44-00438A. The circuit diagram of downloading this model on the Internet is basically a different circuit! Backlight control and drive block SEM2106 circuit, then the drawings are not at all! Later found: BN44-00439A this circuit drawing, the backlight drive circuit is basically the same, the circuit components are marked, but the power supply structure is different. So I referred to this drawing for inspection and repair.
The backlight is always off, the LCD screen is always black, and all the TV repairers know that the backlight circuit is faulty. The target search is mainly the working condition of the backlight board and the circuit of the backlight board.
A: power supply, boot detection drive block circuit SEM2106 VDD voltage (14 feet) is 13V and lighting control voltage 5.3V (16 feet, repaired 4V measured), and PFC voltage 380V. These are basically normal.
Two: Measure the SEM2106 24-pin brightness adjustment voltage (fixed to 4V) and the 1-pin reference voltage (repaired to 5V) are 0V. Explain that this circuit is protected!
Three: 10 feet of SEM2106 is a short circuit to the ground to protect the law, this method is useless here, the lamp may be useful if there is a problem.
Based on the above analysis, I tried my best to find this IC: the related components and conversion circuits around SEM2106. Each component was carpet-likely tested, and even SEM2106 was replaced. There was no result. The repair was in a dilemma!
Later, I read the book "Principles and Analysis of BN44-00260 Two-in-One Board" on page 41 of the 2nd and 3rd editions of "Home Appliance Repair" in 2014. I learned that the backlight does not start to protect, and the circuit behind the high voltage board is abnormal. There are also implications. (The friend who repaired this board encountered difficulties, may wish to also look at it, the principle is more thorough, I will not say here) Then the iron box on the high-voltage board is taken apart and the high-voltage board is tested: high-voltage board The labeled LD13V, VCC13V, and CNT-PRT13V are all normal. Only OVP (overvoltage protection terminal, repaired to 0.4V) is 0V, which is definitely not normal. Seeing that there is only one 10358 operation block on the high voltage board, will this be broken? Decisively removed this block, changed a new LM358 up, and then booted the test machine, and suddenly saw the TV backlight lit up! This mood can't express that kind of joy! It’s really a mountain of water, and there’s no way to go. thanks for watching!
For the convenience of everyone in the future, this circuit drawing is specially issued for reference only to the backlight drive circuit. BN44-00439A.pdf