Model: LC55FT68AC
Screen model: LTA550HF02
Symptoms: Vertical ghosting during boot screen:
After turning on, the first 5 seconds look normal, then the image slowly crawls upwards and stabilizes after 30 seconds with about 50 lines visible.
Even after turning off the power, the screen still shows vertical ghosting. After leaving it off for 24 hours and powering it back on, the same issue occurs again within the first 5 seconds.
This kind of LCD TV repair is not common, so I did some research online and checked forums to gather more ideas. Initially, I thought it was a vertical drive issue, possibly caused by a defective component.
I suspected that a capacitor might be leaking, or there could be a problem with the motherboard’s RAM or logic board connection to the screen.
Since the issue was a ghost image, I didn’t think the power board was the main problem. I started by opening the motherboard, but due to my limited technical skills, I wasn’t sure how to proceed without schematics.
I tried replacing the motherboard with a known working one from a similar model, but the problem remained. It was frustrating—no progress at all.
Next, I moved to the logic board. I tested the 12V and 3.3V voltages, which were both normal. Still, I had no idea where the fault was. So I decided to replace the board again, but this time it also failed.
At this point, I was pretty sure the issue was with the screen itself. I had already spent a lot of time and money, and I didn’t want to give up. The only option left was to remove the screen.
After disassembling the screen, I was shocked. It was an integrated display with the column driver external and the line driver built-in. That meant it couldn't be repaired using a standard pressure screen machine.
I still kept going. I removed the right board's cable and found that the left half of the image was normal, while the right half or the entire frame showed ghosting.
I used an oscilloscope to check CKV1-3 and CKVB1-3 signals. The waveforms were symmetrical, inverted, and each phase was 120° apart.
Since the left side was fine, it suggested a conflict in the built-in dual-line driver chip.
I considered using the remaining functional chips to drive the entire screen, even if it meant a risky fix. I decided to cut the faulty connections and reroute them.
I used a blade to make precise cuts, as any mistake could ruin the screen completely. As shown in the image, I cut CKV1-3 and connected CKVB1-3 instead.
After powering it on, the screen came to life after 3 seconds. It worked!
I took a picture of the repaired screen and ran a 4-hour test. No issues were found.
Summary: Due to limited experience and lack of proper training, I took many wrong turns, leading to wasted time and resources.
I believe the root cause was a displaced or misaligned embedded driver chip, likely due to thermal expansion and contraction of the screen over time.
The chip being built-in made it impossible to fix through regular methods. This approach was a last resort, but it worked well enough—about 85% improvement, which is better than scrapping the unit.
Of course, there are still minor issues, especially in fast-moving or gray scenes, where the image slightly flickers, similar to plasma burn-in. I think the chip may not have enough power or voltage to drive the screen properly.
Samsung uses dual-chip bridges for this reason, which makes sense.
Although not 100% perfect, this repair is a solid solution compared to throwing the whole thing away. I apologize for not being able to upload more images due to space limitations.
That’s it. I’m ready to move on. Thanks for your support!
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