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Any idea what happened the TV?
Was it damaged during a power surge or thunderstorm?
If any liquid has got near the panel itself then it could be fried :\
It seems you have already tried replacing all of the main boards that could cause this problem, so I'll check if the other experts can offer any further input on this.
Hello and sorry you're having problems. Upon reading everything you've posted here, this indicates a bad LED panel in the TV, which is not replaceable- since the panel costs 80% of what the TV cost when new, and are not sold by the manufacturer aside from purchasing a new TV. The T-con, Mainboard and Power Supply have all been replaced and your panel is still not producing any images- so unfortunately this does tell us with certainty that the panel itself in the TV is faulty, and unfortunately, aside from purchasing the exact same model number TV, used, or with a different fault and taking the panel out of that set- this is not a repairable fault.
I'm very sorry for the bad news here and wish there were a quick fix.
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Okay I understand, and that is a good call. If you need further assistance let me know. Please do not forget to click at least a 3 STAR RATING, at the top of the page for my efforts.