1 What do I do from here?
@oldturkey03 i got the same issue now. I disconnected the ribbon cable to the display. Now i hear the startup sound and see the backlight shining. But what do i do from here? Visually the display board at the bottom looks fine.
Update (01/07/24)
I got the Samsung GU50TU8079 mentioned above. I did all the steps you mentioned in your answer.
Disconnected the mainboard from the powerboard.
Backlight shines.
Reconnected the Mainboard.
Error occured.
Disconnected the speakers.
Error occured.
Reconnected the speakers.
Disconnected the power switch.
Error occured.
Reconnected the power switch.
Disconnected the big ribbon cable that lead to the very thin board on the bottom of the tv (i think display)
Error didn't occur and i heard the startup sound. But no image because the display ist disconnected.
Reconnected the ribbon cable.
The thin and long board at the bottom ist split in two with a ribbon cable interconnect. I disconnected the interconnect.
No error and startup sound.
Now i think i know that the problem has to be on either one of the two boards on the bottom.
But these boards have multiple ribbon cables soldered to them leading into the display.
Wich makes repairing or replacing them for me near impossible.
894 
2.3千 
@timbengfort so what have you tried/checked? What exact make is your TV? Why did you remove the ribbon cable on the panel vs the main board on the power board to check teh power board first? It could be a panel issue but we need to know if your panel gets teh right signals and power :-)
oldturkey03 さんによる