Greetings the same thing happened to me with this TV brand but it was when I connected the video via HDMI and the fault was in the MAIN card. You can do several tests to discard the main. To discard the main disconnect it from the source, then make a bridge between standby power on and power inverter, place the power and must turn on the source, check all the voltages and must turn on the lamps, if all this does your problem is in the main Some TV with just disconnecting the main turns on the lamps and starts the source, in others there is that identify the ON / OFF a 10K resistor is placed between ON / OFF and VCC, that power to turn on, check and comment. Do not forget to rate the comments as this will motivate us to continue providing advice, I also invite you to follow me on my YouTube channel where I am placing repairs every so often, I leave you a link for the repair of an LED TV. Greetings.