Hisense LCD TV TLM32V78K start difficult fault repair sharing - android - Phones Developers

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Yesterday at 7 PM, a customer brought in a repaired Hisense LCD TV model TLM32V78K. The main issue was that the TV had trouble starting up. The power indicator light, which is usually green, didn't turn on. Sometimes it would start after several attempts, but once it did, it worked normally and didn’t shut down again. The customer mentioned that the after-sales service from Hisense took about a week to fix the board. I assumed the price might be too high for them to accept. They also said the problem had occurred before, and they were a bit hesitant. That’s why they came to me, asking if I could fix it and what the cost would be. I initially quoted orange-black-brown, but we eventually settled on red-yellow-brown, and they agreed to proceed with the repair.

At first, I thought the issue might be related to a faulty capacitor in the power supply. I opened the back cover and checked the capacitors—they looked fine. So I moved on to voltage testing. The TV wasn’t powering on at all. After connecting it, I measured 5V on the 5VS line, and the ON pin had around 3.5V. However, there was no 12V or 24V output. The voltage across the PFC filter capacitor was only 360V, but it should have been around 380V. I wondered if this was due to a leakage in the sampling resistor.

I didn’t spend much time thinking about it and decided to check the sampling resistors. After turning off the power, I noticed they were all soldered down. I carefully removed the solder and re-soldered them. Then I tried powering it on again. After a few minutes, the backlight turned on! I measured the PFC voltage again, and it had risen to 380V. The signal line showed normal behavior, and after a few more on/off cycles, the TV started reliably.

This morning, the customer came to pick up the TV. When I told them it was fixed, their expression was very excited. They thanked me for the help and seemed satisfied with the outcome.