I was given a Changhong LCD TV model LT24610 that wouldn’t start up twice. The previous technician had already done some repairs and suspected the motherboard as the issue. Let me take a closer look. First, I opened the TV and checked the power supply section. After testing, the voltages on the motherboard were all normal: VDDP3.3V, AVDD3.3V, VDDR2.6V, VDDC1.26V, etc. No voltage jumps or abnormalities were found. However, the screen still didn’t light up, and there was no backlight activation. I also double-checked the crystal oscillator Y1 and the reset transistor Q22, but nothing suspicious was found at the time. At this point, things were getting confusing. The technician had already reflashed the system, so I needed to dig deeper.
I focused on the user memory chip U2624LC64. After checking, I found that the SDA voltage on pin 5 was 4.58V, which was higher than expected. Then, I checked the SCL voltage on pin 6, which was only 2.42V. That was strange. Next, I measured the resistance from pin 5 to ground and found it was around 14.8K ohms, while pin 6 to ground was 5.5K ohms. This suggested a possible short or a faulty component on the control lines. I cleaned the SDA and SCL traces and examined the board closely. Here’s what I saw:
After soldering resistors R156, R251, and R272, I tested the resistance again. When R272 was re-soldered, the resistance of the SCL trace to ground returned to normal. This indicated that the problem was in the tuner section. I removed the high-frequency head and tested the capacitor that suppresses glitch interference on the fourth pin of the SCL line. It turned out that the capacitor wasn't being used. I replaced it, reinstalled the tuner, and did a final test. The TV worked perfectly after that!
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