Hi Lew,
That could be a bit curly as LG service manuals are about as useful as a jockstrap in a blizzard. The LED driver board may be separate or it may be incorporated into the power supply, but find the lead that enters the back side of the panel from this board. It may be 2,3 or 4 pairs of wire or 1 or 2 flat flexie cables. The leads will be in pairs, 1 lead of each pair supplying volts to an LED strip or strips, the other an earth return that acts as an error sensor. The first will have high V, the second near 0V.
Measure the voltages wrt chassis earth at the connector on the board for a few seconds at the moment you switch the tv on. The hi-V ones should rise to a particular level, then drop off a bit and settle down. The voltages may also be marked at the plug on the board or marked something like L1+ and L1 for each pair and you're looking for a comparison of the hi-Vs. Not easy to describe without schematics or a board, but I'm home ATM.
If you find a hi-V that rises, but stays at that high level and doesn't drop back down, that lead will be feeding a faulty LED strip (probably an open LED) because there is no load on it. As the LED strips ignite they will gobble up some of the voltage. Some strips may be fed at a different voltage level to others. Just look for the drop-back in volts at the initial switch-on process to identify a strip that isn't drawing current ie it is inoperative due to a faulty LED or LEDs.
Bruce
