My TV screen is very dim, but I don't know my next step

I currently have a problem. I have a Westinghouse dwm40f2g1 non-smart. The picture is dim. I have no experience with this stuff yet. But I took it apart and put it back. The motherboard looked in tact, but I couldn't find a backlight inverter. As soon opened it. I realized the inside was hollow. But that means the only other board is this long one on the bottom but it doesn't look anything like the one online I saw for the inverter. Help