I was called to repair 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 burned areas. Here's a photo for reference:
When I measured the voltage on the upper screen’s 12V supply, it read zero, which indicated a problem in the screen power supply circuit. I tested the resistance between the red line and ground on the motherboard, and everything looked normal—no short circuits. According to the user, this same issue happened before, and another technician replaced the motherboard. However, within three months, the same problem occurred again. It seems that just replacing the board isn’t always the solution. There must be an underlying issue that hasn’t been found yet. But what could it be?
I checked the logic board thoroughly and didn’t see any obvious damage. I removed the screen cables from both ends and tested them, and there was no short between the connectors.
At first, I couldn’t find anything wrong. I tested each terminal, filter capacitor, and voltage regulator on the logic board, and nothing showed a short circuit. Then, something strange happened. When I connected both ends of the screen cable and measured the power supply side of the logic board, the resistance was zero! Oh, now I knew where the problem was.
The fault was hidden, so I needed to approach it carefully. I decided to isolate parts step by step. 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 and found a short. I carefully disconnected the screen from the logic board, and both components seemed fine. But when I plugged the screen cable back in and lifted the logic board connector slightly, I found a short circuit. If I released it or pressed it lightly, everything was normal. So the problem was right here.
It turned out that when the socket was slightly lifted, the screen power line came into contact with the metal part of the socket, causing a short circuit that burned the motherboard. Fixing it was simple.
I just raised the metal sheet a bit, reinserted the screen cable, and shook it a little. Everything worked fine. Then 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 you’re not careful. If I had just replaced the motherboard without checking further, I would have wasted time and money. Always take your time to investigate thoroughly before making replacements. Sometimes, the real problem is hiding in plain sight.
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