A few days ago, a friend sent me an Haihaixin LCD TV model LED39K300J for repair. The issue was a gray screen — the backlight was on, but there was no image. Another friend suggested it might be a logic board problem, so he bought and replaced the logic board. After replacing it, the issue remained. I decided to take a closer look.
First, I checked the mainboard voltages: 12V, 5.1V, 3.3V, and 1.8V all looked good. Then I checked the logic board's 12V supply, which was also normal. But when I measured the VGH and VGL voltage points, they were at 0V. Since the logic board had already been replaced, I ruled that out and started suspecting the screen or the screen board.
The logic board connected to the screen with a double-row cable. I disconnected the cable between the logic board and the screen and tested the VGH voltage again. It came back to 25V, which made me think the screen board might be shorted or in protection mode.
After removing the screen cable, the voltage was normal, and the screen lit up. The screen itself seemed fine, so I concluded the problem was definitely with the screen board.
I didn’t have much experience repairing screen boards, but I decided to give it a try. I opened the screen and examined the components. The board had tiny and complex parts. I first checked for any leaking capacitors and found one, a patch capacitor labeled C20, which was severely leaking and almost shorted. I removed it and measured its leakage resistance — it was only around 20 ohms. That was clearly bad.
Since I didn’t know the exact capacitance value of the faulty capacitor, I replaced it with a similar-sized one. After reassembling everything, the TV worked! The blue screen appeared, and the signal was perfect. It was a satisfying moment after a long troubleshooting process. Dsp Speaker,New Professional Speaker,Performance Speaker With Dsp,Active Speaker For Outdoor NINGBO RFUN AUDIO TECHNOLOGY CO.,LTD , https://www.mosensound.com