When trying to control a LG 65UV341C by RS232 we have seen that turning the screen on is not possible until you have sent the power off command.
So here is what you do.
- Disconnect all power for the display and the control system.
- Connect the control system to the screen.
- Connect power to control system and then the display.
- Turn on the screen with the included IR remote.
- Send the RS-232 "Power off" command to the display.
Now you should be able to turn on the LG 65UV341C by RS232.