99.9% certain that the issue behind your problem is not X10 signal strength or powerline noise from the TV - but rather IR interference from the LCD/Plasma TV. Try moving or shielding the IR543 such that the TV doesn't have line of sight to the IR sensor on the IR543. It's not always easy - as the IR noise from the TV will reflect off walls and pictures. Check out the IR repeater gear available and you'll find plasma proof sensors that can filter out the noise from LCD and plasma TVs. Good Luck!