PN50A650T1FXZA - Sound but No picture

I have sound but no picture on my Samsung PN50A650T1FXZA.

All fuses are good.

Power Supply - VA and VS voltages good

YMain - VSC Voltage bouncing around

XMain - VB Voltage bouncing around

If ribbon cable from Ymain to logic board disconnected, Ymain voltages good.

If ribbon cable from Xmain to logic board disconnected, Xmain voltages good.

If both Y & X ribbon cables to logic board disconnected, all voltages good.

Tried to get test patterns to come up on screen.

Shorted PS_On & Ground on power cable from Power Supply to Main.

Placed jumper on pins 3 & 4 on Logic Board.

Disconnected video cable from Main to Logic.

NOTHING!

Suspect logic board. Request any comments that may help. Thanks.