Actual combat: Hisense LED39K300J LCD TV gray screen failure - Home Appliances

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A few days ago, a friend sent me a 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 that the problem might be with the logic board, so he bought a new one and replaced it. However, after disassembling the unit, I started checking step by step. First, I tested the mainboard voltages: 12V, 5.1V, 3.3V, and 1.8V were all normal. Then I checked the logic board's 12V supply, which also looked fine. But when I measured the VGH and VGL voltage points, I found VGH was at 0V.

Since the logic board had already been replaced by someone else, I didn’t think the issue was there anymore. I suspected something was wrong with the panel or the panel board. The logic board was connected to the screen via a double-row cable. So, I disconnected the cable between the logic board and the screen. After doing this, the VGH voltage returned to 25V, which made me think the panel board might have a short circuit or protection issue.

To confirm, I removed the panel cable and tested again. The VGH voltage was now normal, and the screen lit up. The screen itself seemed to be working fine, but the image wasn’t displaying properly. This strongly indicated a problem with the panel board. I didn’t have much experience repairing panel boards, so I decided to open it up and take a closer look. The components on the board were very small and complex. My first thought was to check for any leaking capacitors.

While inspecting, I found a surface-mount capacitor (C20) that was seriously leaking, almost shorted. I removed it and measured its resistance, which was only around 20 ohms. That was definitely not normal. I didn't know the exact capacitance value of the original component, so I replaced it with a similar-sized capacitor. After reassembly, the TV came back to life — the blue screen appeared, and the signal was working perfectly! It was a relief to finally fix the issue.

This experience taught me that even small components like capacitors can cause major problems. It also reinforced the importance of methodical troubleshooting, especially when dealing with complex electronics. If you're facing a similar issue, don’t rush into replacing expensive parts — sometimes a simple capacitor can be the real culprit.