TCL LCD TV L40E9F motherboard can not boot repair case - appliance repair - Database & Sql Blog Articles

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A few days ago, I received a TCL L40E9F LCD TV that could not be turned on, the blue light flashed, no sound, no image, and the power supply board 12V, 24V, 5V were all normal. Remove the power board, unplug the motherboard cable, keep the high-voltage board connection, short-circuit the standby 5V and standby control and backlight control, the backlight lights up, make sure the power board is normal, the fault is on the motherboard, then remove the motherboard and button remote control board Back to the store for maintenance, because the home has a identical power board, so the power board does not have to be removed. Go back to the store and connect the power board to measure the motherboard voltage, 5V, 3.3V, 2.6V normal, touch the various voltage regulator blocks and chips by hand, and find that the 2.6V voltage regulator block is very hot, it will be hot for a few seconds after booting, 2.6V voltage Slowly falling. Remove the main chip shield, touch the main chip, heat quickly, obviously not normal, remove the 2.6V regulator block output inductor, measuring current reaches 1A or so, no wonder the main chip and 2.6V regulator block is so hot, it is possible The main chip is finished, this is troublesome, the chip has more than two hundred feet, and there is a heat sink at the bottom. As far as I am dizzy, the welding is a big project, and it is not necessarily successful. Regardless of him, first smoke the cigarette and say, while thinking, not right, how to reduce a voltage, the main chip generally has a voltage of more than one volt, powered by three-terminal regulator, how this machine does not have this three-terminal Regulatory. So re-measure the circular inductance on the motherboard, and found that there is no voltage on both sides of the inductor. This is a major discovery. Maybe the fault is here. Under normal circumstances, the main chip is stepped down from 5V to a little more than one volt. The machine should be no exception. So trace the power supply of the inductor and the step-down chip, and finally found that the new continent, 5V passed through the silica gel and then came out, and carefully scraped the silica gel, found that the following is a resistance of 000, a measurement open circuit, suddenly overjoyed, it is him. Looking for a long time, did not find this resistance, and then measured the 5V load, no short circuit, simply shorted him, forget him, big deal, smoke. Reconnect the power board and button remote control board, power on, with the remote control switch, the indicator light is on and off, control is free, and the repair is successful. Then touch the main chip and the 2.6V three-terminal regulator, no fever. Yesterday, I took the motherboard to the customer's home and the test machine was all right. It’s really no doubt that there is no way to reclaim the mountains and heavy waters. There is still a question here, why is the main chip missing a voltage, and the 2.6V supply current becomes so large, why? why? why?