I was tasked with repairing a 32-inch LCD TV that had a gray screen but still produced sound. After opening the cover, I noticed that the motherboard had some localized burning. Please refer to the image below for reference:
When I tested the voltage on the upper screen’s 12V line, it showed 0 volts, which pointed to an issue in the screen power supply circuit. I checked the resistance between the red line and ground on the motherboard, and it was normal—no short circuit detected. According to the user, the same problem occurred not long ago, and another repair shop replaced the motherboard. However, within three months, the same issue returned. This made me think that replacing the board too quickly might not be the solution. There must be something else causing this.
I examined the logic board closely but didn’t see any obvious issues. I removed the screen cables from both ends and tested them, and there was no short between the connectors.
At first, everything looked fine when I probed around. I tested each terminal, filter capacitor, and voltage regulator block on the logic board, and none of them showed a short. But then, something strange happened. When I connected both ends of the screen cable and measured the power supply end of the logic board, the resistance was zero! That was a big clue. The problem was hiding right under my nose.
Since the fault was so hidden, I decided to approach it carefully, like a detective. I used a methodical, step-by-step approach. I gently unplugged the screen cable from the motherboard and measured the resistance at the plug-in point. Then I tested the screen cable itself for a short. After carefully disconnecting the screen from the logic board, I found that neither component was faulty. But when I plugged the screen cable back in and lifted the logic board’s connector slightly, the resistance dropped to zero again. It was normal when I released it or pressed it slightly. So the problem was clearly in the connection.
It turned out that when the socket was slightly lifted, the screen power supply line came into contact with the metal part of the socket, causing a short circuit that burned the motherboard. The fix was simple.
I just needed to lift the metal sheet a little bit, reinsert the screen cable, and shake it slightly to ensure it was secure. Once that was done, everything worked perfectly. I replaced the motherboard and handed the TV back to the customer.
This kind of hidden short-circuit fault is rare and easy to miss. If I had just replaced the motherboard without checking the connections thoroughly, I would have wasted time and money. Always take your time, follow the clues, and don’t jump to conclusions. Sometimes the real problem is right in front of you, but you just need to look closer.
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