Have TV Questions? Ask a TV Technician
Hello, Sorry you're having problems. Offhand this would be caused by weak/failing LED strips inside of the LCD panel (which are what light the screen). The only other component in the TV that works to light the screen is the power supply board - however the entire screen would be black until the set warms up if that were the case generally. In order to determine which is causing this with certainty, a TV tech will need to test the power supply board's LED +/- backlight voltages while the screen is mostly black to see if they are up to spec. If they are not - then the power supply board will need to be replaced, which is on average a $250 repair on a 55" Vizio. However if they are up to spec then the LED strips inside of the panel need to be replaced, and this is quite expensive as it requires complete rebuilding of the screen, and also of the TV. Some shops will deem the set non-repairable for this fault, and others will charge closer to $400 parts and labor to rebuild the screen )in which case it's not cost effective to repair since a brand new 55" Vizio starts at around $450-$500.
If you would like to inquire about repairs, or seek another opinion, you can use the link below to locate a shop in your area:
Other than that, I'm sorry for the bad news and wish there were a quick fix.
If you need further assistance let me know. Before you go, PLEASE DO click at least a 3 STAR RATING, at the top of your screen (scroll up the page to get to the STARS). That is how I am credited for my efforts by the site. You can follow up any time as needed at no additional cost.
Please view my answer posted above.
Do you need further assistance with this?