32-inch Konka LCD TV cold boot protection without backlight, sound failure repair example - android - Phones Developers

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Today, I received a 32-inch Konka LCD TV with an issue where it would not power on properly. It had a cold boot protection, meaning the backlight and sound were completely off. Sometimes, after a second attempt, it would turn on normally, but other times it wouldn’t. I spoke with the customer about the cost and suggested replacing the power supply board (model 34006601). After some negotiation, the customer decided to go ahead with repairing the board instead.

I started by disassembling the unit and checking the voltages. At first, everything seemed normal, but I was worried about interference that might be causing the backlight to remain dim. Later, I came across a similar model with the same problem on a forum. I tried shorting resistor R773, but the boot issue remained. Then I tested capacitor C756 by increasing its capacity, but the problem still persisted. I also noticed that there was aluminum foil attached to the back of the logic board. None of these steps worked, and I ruled out any soldering issues. I was starting to feel discouraged.

After two hours of troubleshooting, I accidentally noticed that the backlight would flicker briefly before booting, or sometimes not come on at all. The screen was a plastic one, so I wondered if the internal aluminum foil had broken. This reminded me of a similar issue I had fixed on a Hisense TV before.

I decided to take apart the screen. It was a real mess—there were ten broken pieces in total, and six of them were damaged. I replaced the aluminum foil and added vertical ones on both sides. Once I reinstalled the screen, I tested the TV again, and the issue was gone! I let it sit for half an hour, testing every 30 minutes, and it worked perfectly each time. I felt relieved after such a tough day.

This kind of fault was really tricky. No matter how many boards I swapped, it wasn't until I removed the screen and fixed the aluminum foil that the problem was finally resolved. It was a hard case, but after a full day of work, I managed to fix it.