When I turn on the tv, the sound comes on, but no picture

Hello,

Problem is in either power supply or the Y-Sustain board.

The Y-Sustain is a relatively large board out of which go connections to the side of the display; it's therefore closer to either the left or the right side of the display, has at least one rather large heat sink on it and fat power cables connecting it to the main power supply.

Often there are fuses on that board - one or more. Check those.

if they are blown you can try to replace them, but expect them to blow again - usually the whole board needs to be replaced.
I hope this will helpout