46-inch TCL LCD TV logic board fault repair example - Home Appliances

Recently, a middle-aged customer came into the store and asked about a TCL L46P10FBEG TV that had a dark image at times. The brightness wasn't sufficient, but sometimes it worked fine. The after-sales service mentioned it might be a screen issue, and suggested that XX Ocean could repair it. They asked me to check it, but they wanted an inspection fee upfront.

During the visual inspection, the image was dark when the problem occurred, with motion trailing and slow refresh rate, as if the picture was stuck. When the image was normal, the backlight was fine, no protection was triggered, and the power output (5V, 12V, 24V) was all within normal range. The filtering capacitors on the motherboard showed no bulging or discoloration. The voltages on the mainboard (5V, 3.3V, 1.8V) and the logic board (12V) were also okay.

I then checked the voltage values at several key points on the logic board. The DC-AC conversion point showed VGL = -7V, VGH = 26V, and VDD = 16V. The drive IC's power supply was 3.3V, which seemed fine. But something was still off—obviously, the gate-on voltage was the issue.

I took the screen apart and looked at the sideboard circuit. It was in very good condition, no corrosion. I just checked the voltage again. When the image trailed, one of the VGH voltages dropped from 26V to -4.6V. That was the problem! I checked the cable from the logic board to the screen connector, and found that instead of 26V, it was reading -4.6V. However, the DC-AC conversion was still providing 26V. The resistance to ground appeared normal, so there was no leakage. It looked like there was a bad contact between the lines—probably due to thin wires and lack of cleaning.

Solution: I used a flying wire with a 22K resistor, and after testing, the TV worked perfectly. I haven’t received any feedback yet, but it should be fine now.

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