How can I repair my LG 55UL6200 that suddenly will not power on?
This tv will be so easy to diagnose, a 4th grader with a multi meter could fix it. There are only 3 simple tests to do, for starters make sure the power supply is working, not sure why you would have ordered another board without testing the one you have!! Use frame as ground, push the power button, put red or hot lead of multi meter to pin 8 or 9 on CN 802, you need 12 VDC there, anything from 11.5 to 12.5 is good, if you see that voltage the power board is working, see how easy it is to trouble shoot the power board and I'm guessing it will be ok as this power board almost never gives issues. Next test, on the main board look for the the digital optical audio input jack, take a small screwdriver and push the cover open and you should see a red light inside of it, if you see that the main board is working, this model has some issues with the main board BGA IC need reflowing but the simple test of looking for the red light inside the audio optical jack, now with process of elimination and the fact 90% of LED TV failures are the backlights you have come down to them being bad and needing to be replaced. You will need to remove the frame and the panel to get at the lamps, be VERY careful handling the panel, it's very fragile, there will be a piece of plexi glass and 2 or 3 defuse screens after you get the panel out that need removing, put tape around them and mark the top, as you need to put them back in the same way they came out. Best place to order parts is shopjimmy,com, I looked and they have them in stock for $50 plus shipping. See diagnosing a TV is very simple as long as you know what to look for and in what order to do the various steps needed. What is happening is, you power the set on, see the message at the top come on for a second and go off, the power board has the inverter built into it, when the set is turned on it looks for the proper DC voltage and current draw to the backlights, your current is higher than allowed so the inverter is shut down, resulting in no backlights, and no it's not a fault of the power supply. Good luck!