How do I repair the power supply on my LG RE44SZ21RB tv?

My LG RE44SZ21RB DLP tv has developed a problem on the power supply. When powering up, the orange light flashes for a while then goes back to stand by. I have isolated the fault by changing the power supply for a known working one, that cured the problem, but I now need to fix the original. It has 240VAC going into the board, but nothing coming out to the lamp control board.