The fault phenomenon is that the boot screen is instantaneous (about 1 second) and then the black screen is immediately. This machine is composed of four boards for the Samsung 40-inch LCD TV: digital signal processing board + main power high voltage two-in-one power board + screen drive logic board + CCFL lamp backlight (see photo) Switch & Socket,Sockets And Switches,Brass Plug Sockets,Light Switches And Sockets WENZHOU TENGCAI ELECTRIC CO.,LTD , https://www.tengcaielectric.com
According to the routine inspection ideas and methods, this phenomenon is mainly caused by the feedback circuit of the high voltage board. For example, if the high voltage is too high, the protection, the feedback circuit has problems, resulting in no feedback voltage, excessive feedback current, backlight damage or poor contact. When the high-voltage output is unbalanced, the high-voltage inverter circuit will stop oscillating and finally stop the high-voltage output display black screen, IC output is too high, etc. This will cause the problem to be checked. The signal sent to the high-voltage board by the motherboard is normal. This machine uses a 20-lamp high-voltage board circuit. The high voltage and backlight panels use the X1692B solution. The overcurrent and overvoltage protection circuit is forced to be lit by the short circuit method. All the lamps can be lit, but one of the lamps is particularly bright, and the sampling transformer of the lamp is taken. Smoke damage (apparently caused by excessive current of the lamp), it is thought that it is the problem of the lamp, the socket of the lamp is unplugged, and the other lamp has the same problem and the rule is not found. The backlight and high-voltage board are still faulty. Finally, it is decided to disassemble and check the lamp. (The risk of disassembling the lamp is very high, and the LCD screen needs to be removed. If you make a mistake, you may scrap the LCD screen. After disassembling, you will find that the new continent: the middle part of the common grounding wire of 20 lamps has been blown off by high voltage and blackened (see photo), and it is connected with wires to repair the fault. Exclude the reason after the analysis: the manufacturer has problems in the production process. Here, the phenomenon of solder false soldering, due to the high pressure state, has not been affected by the slight ignition condition at the beginning, so the manufacturer will not be found during the production test. The problem, after the user uses it, over time, the fire will slowly break down the board until the fault occurs.
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