similar trouble here to many other vizios on vizio model VO47L FHDTV10A
power supply makes 5v but not 12 or 24
found if i jumper "pson " line, pin 1 on cn3 on power supply board relay clicks and 12 & 24 appear so i think power supply board is okay
poking at main board found it real sensitive in upper left corner at J2 where the cable plugs in that goes down to switches and IR board. touching board makes relay click.
unplugged and plugged back in J2 with power on and TV came on and ran for about ten minutes. did that a couple times.
when i jiggle j2 i hear the power supply relay click
have main board out now looking around main board (the big green one) j2 with magnifying glass for something broke or burnt