Samsung UA50J5500: Standby voltage fluctuating

[keerthi123]

I am working with a Samsung UA50J5500 and backlight works when logic board disconnected also standby power steady at 13.00V. When connected to logic board, 13 goes to 9 and 13 again drop to 9 and goes on as a cycle, what are the possibilities?
logic board: BN41-0235, PSU:  BN44-00704E