Ah ha. Excellent.
I've worked with your TV a number of times on this exact issue, and this is caused by the Y-main aka Y-sustain board.
With this chassis, though, you should replace the upper and lower buffers, as well. If you don't replace all 3, you're throwing your money away.
I've outlined the boards you need to replace:
Your TV used a couple different versions of these boards, so be sure to get the part number from the boards themselves before you look for replacements. That way, you can be sure you're ordering the right ones. I've listed some suppliers, below.New parts
This could get expensive, but look up the parts and decide for yourself if it's too expensive.
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