hi,had the same problem with a lg v6 pdp.check for a short between vs and ground on the bottom buffer boards.this also dragged my 15v from ysus down to 9v.
It turned out to be a bad ic on one of the ribbon cables attatched to the panel.
not sure which panel your set uses but i could not see a way to successfully change these ic's on a v6.
good luck.
steve