Changhong LCD TV iTV32830EX after the second boot, there is no sound maintenance example sharing - Home Appliances

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Resistors are one of the most commonly used components when repairing electronic devices at home. In the past, when fixing CRT TVs, resistor failures usually showed that their resistance values increased or became open circuits. For example, resistors in the power supply section, like the start-up resistor, the load resistor on the C pole of the discharge tube, and the sampling resistor for the ABL circuit in the color signal were often problematic. However, while working on LCD TVs, I noticed something different — many resistors had lower resistance values than expected! Here's an example of a resistor with a reduced value, and I'd like to share it with you. I was working on a Changhong iTV32830EX TV, and after the second boot, there was no sound. Upon disassembling the unit, I checked the voltage at the BL-ON/OFF pin of the constant current board socket and found it to be 0V. The ground resistance wasn't shorted, so the issue must be in the mainboard's JUC7.820.00033862 BL-ON/OFF branch. After checking the motherboard, I discovered that the BL-ON/OFF signal was controlled by the N-pole transistor Q3 and the C-pole of the screen printing H1A. The B-pole of Q3 had a steady 0.68V after the second power-on, which caused Q3 to be saturated and output a low level at its C-pole. As a result, the constant current board didn’t function properly. To test further, I shorted the Q3 pin, and the backlight turned on normally, with an image appearing. This confirmed that Q3, the constant current board, and the LED strips were all working fine. Then, I checked the B-pole of Q3 and quickly found that the external pull-up resistor R4944K7 on the BL-ON/OFF pin of the main chip had dropped to just a few hundred ohms. Replacing R494 fixed the issue, and the TV worked perfectly after testing. Thanks for watching!