Phillips TV turns , has sound and backlights but no pictiure

I have a Phillips TV model number 42PFL7332D/37. When I first turn it on I get sound, backlights and the picture comes on for a few seconds and then the screen goes black but it still has sound and back lights . I have replaced the main board, the backlight inverter boards and the T con board so far. Is the any voltages checks I can test on the power board.