The TCL LCD TV model L40E9SHBD is experiencing an issue where the blue light is not turning on, although the machine's blue light indicator is on. After checking the voltage levels of each voltage regulator block, it was found that the reset voltage of the main chip is abnormal, fluctuating around 2V. Normally, the reset pin should be at a high level, and when the system is operating correctly, the reset voltage should be close to 0V. To troubleshoot, the reset circuit was temporarily removed, and a manual reset was performed by connecting 5V directly to the reset pin of the main chip. However, the fault persisted after this step. Further testing showed that when the reset circuit was disconnected, the voltage at the reset pin was still fluctuating around 2V, indicating a potential issue with the main chip itself. As a next step, a bleeder resistor was added to the reset pin, connecting it to ground through a 750-ohm resistor. This action successfully eliminated the voltage fluctuation. After performing a manual reset again, the backlight turned on, confirming that the issue had been resolved. The original reset circuit was then reconnected, and the TV functioned normally without any further issues. Several photos were taken during the repair process for documentation purposes. These images show the internal components and the steps taken to diagnose and fix the problem.
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Kunshan Bolun Automation Equipment Co., Ltd , https://www.bolunmachinery.com