Sony XBR-55x900C - Dark, No Music, No LED after mainboard replaced

I have XBR-55X900C with vertical lines (no logo etc) on screen with music. I replaced the mainboard and get blank screen, no music, no LED as if no power. When I switch back to the old mainboard, I get the original condition - vertical lines on screen and music.

I have previously replaced the T-Con so it am convinced that the mainboard is bad but replacement condition is throwing me.