I had the same thing with a samsung as well.
In that tv the problem was a bad ( polluted) t con flat cable. i cleaned the contacts with isopropyl. first remove the dust.
if this doesn't work : try to check the Pcb of the T con board. probably a bad IC. ( as15.. )(most of the time)
try to measure out first if thats possible.
if you are not sure, send us some pictures when you open the tv. we will show you what the t con board is.
Kind regards,
kevin