Hello Evan,
Thank you for sharing the details about your LG 55UK5090PUA TV issue. It sounds like you've already taken some significant steps by replacing the Main Board, which is great troubleshooting.
Given that you can see the backlights are on and you have sound, here are a few additional things you might want to check:
1. **Connections**: Double-check that all cables, especially HDMI, are securely connected. Try switching HDMI ports or using a different cable to rule out any issues with the current setup.
2. **Backlight and Panel**: Since the backlight is working, the problem might be with the LCD panel or a component related to video processing. This could be more complex to diagnose without specialized tools.
3. **Flex Cords**: Sometimes, issues like this can be caused by problems in the flex cords connecting the screen to the T-Con board. Inspecting these for any damage or short circuits might be worth a look.
4. **Power Cycle and Reset**: If you haven't already, try unplugging the TV, holding the power button for about 30 seconds to discharge any residual power, and then plugging it back in. This can sometimes resolve unexpected issues.
5. **Professional Help**: If none of these steps resolve the issue, it might be time to consult a professional TV repair service. They can provide a more detailed diagnosis and potentially fix the problem.
I hope these suggestions help you move forward with resolving the issue!
Best regards,
[Abel Sileshi]