Wow. DON’T go opening your TV, on this person’s ‘whim’... GEEZ!
There’s a LOT more they could have asked and looked into, before asking you to go above & beyond.
Googling the model & issue would have revealed (if they had bothered) that this is a common complaint with the 2017 models-on, and software/feature related (unless you actually have a defect)
Also, he could have asked is it constant or re-occuring(?)
I also have the same frustration with the same model and why I came here.
This happens EVERY evening, around 9pm, (During the day it’s normal again)
Yes, I disabled power-saving and it only got a shade lighter.. so particularly infuriating.
Lastly, I’d ask have you tried other modes, such as launching a video game or app through PC/HDMI(?)
When I launch a game, it becomes bright again and normal.. But the desktop is dim, just like TV mode.
This is another BIG clue, it’s NOT a hardware issue..
Please drop the screwdriver & back away from the set!!
This person isn’t going to replace your set, if something goes wrong & I bet taking it apart won’t lead to anything.. (good that is)
-Best wishes, just keeping it real