Today, I had a tough repair on a Skyworth LCD TV model LED46E70RD. The issue was that the indicator light wouldn’t stay on, and sometimes it would turn on briefly, but the screen remained dark with only a faint speaker noise. I had fixed this same model two days ago, and the user came back again with the same problem.
When I arrived at the user's home, the power light wasn't bright. After opening the case, I checked all the voltages: 380V, 24V, 12V, and 5V were all normal. The STB signal was high, but P-ON/OFF voltage was missing. After unplugging and re-plugging the screen cable, the blue light turned on, and the backlight worked. The TV played background music, so I thought it was fixed. But the user reported that the logic circuit was faulty, and I gave them a quote. They agreed, and I replaced the screen cable.
After running the TV for over an hour without any issues, I felt confident. But then, the user called again saying the TV wasn’t working again. I went back to check. All voltages were normal again, including 5V, 3.3V, 2.5V, and 1.8V on the mainboard. When I plugged and unplugged the screen cable, it worked again. This was really confusing.
I noticed that the screen would go off when the TV was turned on, even though the blue light was still flickering. It seemed like a motherboard issue, but why was the backlight turning off? Could it be a broken LED strip or a problem with the power board? I checked the solder joints on the power board but found nothing wrong. Then I focused on the motherboard, pressing it gently. The main chip was booting, but it still didn’t work. However, I noticed the chip was extremely hot.
After repeated on/off cycles, I managed to get the TV to boot normally, but the speaker made a strange sound, similar to an old TV with no audio. The screen stayed black. At this point, I discussed with the user about replacing the motherboard. They agreed, but I insisted on doing the first repair free of charge. If it didn’t fix the issue, they wouldn’t have to pay for the new board.
The user was very understanding and appreciated my honesty. I immediately removed the two screws, took the motherboard out, and headed home.
Now, let me show you the process step by step. First, I used a heat gun to warm up the heatsink on the chip for a few minutes. I kept the temperature under 280°C. After heating, I carefully lowered the heatsink using tweezers. Then, I used a scalpel to cut the edges of the chip and covered the surrounding small parts with aluminum foil.
Next, I applied BGA solder paste to the bottom of the chip using a heat gun. After matching it on the rework station, I started heating it until a slight smoke appeared. I added more solder paste while continuing to heat the chip. Once the temperature reached 240°C, I gently touched the chip with tweezers and continued adding solder until the tweezers could easily touch the chip.
After cooling down, I removed the motherboard and ran it for several hours, repeatedly pressing the chip. Everything worked fine, and the repair was complete.
Here are some photos from the process:
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