I'm working on a Changhong LCD TV model LT24610 that won't start up properly. The user mentioned it doesn’t power on twice, and a previous technician tried to fix the motherboard but couldn’t find the issue. I decided to take a closer look myself. First, I opened the TV and checked the power supply section. I tested several key voltages: VDDP3.3V, AVDD3.3V, VDDR2.6V, and VDDC1.26V. All of them were stable and within normal ranges. No signs of voltage spikes or drops were found. However, the screen still didn’t light up, and there was no backlight activation. I also double-checked the reset signal from Q22 and the crystal oscillator Y1, but nothing suspicious was found at this stage. At this point, I started suspecting a more complex problem. The technician had already re-flashed the device, so I needed to dig deeper. I focused on the user memory chip U2624LC64. After testing, I noticed something unusual: the SDA voltage on pin 5 was 4.58V, while the SCL voltage on pin 6 was only 2.42V. That was definitely out of the ordinary. Next, I measured the resistance from pins 5 and 6 to ground. Pin 5 showed 14.8KΩ, and pin 6 showed 5.5KΩ. That didn’t seem right either. I cleaned the SDA and SCL traces on the board and examined the control lines closely. After soldering resistors R156, R251, and R272, I rechecked the resistance. When I soldered R272, the resistance of the SCL trace to ground returned to normal. This indicated a fault in the tuner section. I removed the high-frequency head and tested the capacitor connected to the SCL pin (pin 4) of the tuner. It turned out that the capacitor used for noise suppression was not functioning. I replaced it and reinstalled the tuner. After that, the TV powered on normally, and everything worked as expected. The repair was successful, and the customer was very satisfied with the result.
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