Disconnect the plug between power and main. Just plug AC cord, you should see back light comes out.
If not, your LED backlight stripes mostly like dead. ASK before you place an order. The item "BN44-00612B BN41-01958B for UN75F6300 UN75F6400, 100% GOOD" is in sale since Saturday, February 13, 2021.
This item is in the category "Consumer Electronics\TV, Video & Home Audio\TV, Video & Audio Parts\TV Boards, Parts & Components". The seller is "tvfixwayne" and is located in Sidney, British Columbia. This item can be shipped to United States, Canada.