TV is Vizio E55-E1. The backlight started going out in the upper left corner and spread to most of the left third of the screen. Is this likely a problem with the driver board or the LEDs themselves? Thanks.

It is possible that the issue you are experiencing with your Vizio M55Q6M TV could be caused by a problem with the backlight. The backlight is responsible for illuminating the display on the TV, so if it is not functioning properly it can cause uneven lighting or areas of the screen to appear darker than others.
Other potential causes of the issue you are describing could include a problem with the display panel itself, or an issue with the TV's software or firmware.

The Vizio "E" (economy) series sets have local diming, on most brands if some of the lamps go bad the screen is black but not on these model Vizio TV's, for this reason it's harder to troubleshoot the set for possible bad backlights or backlight inverter issues. If you have a LED backlight tester you can test each zone at the backlight connector off the inverter board to see if each is working, without a tester you're going to need to remove the panel then move strips that don't light to ones that do and see if it's the strips bad or inverter issues.

Hi Sean...It's your backlight strips that need replacing. Best place to buy them is shopjimmy.com. You have some shorted lamp buttons that's causing the power supply inverter to shut down from over current

This model TV had issues with the connector going from the power supply to the LED driver board, the solder contacts on the back of the board break loose, you can either solder the contacts if you have the means to do that or order a new board. If you're able to solder it, you will need a small tip for the iron and use lots of flux or the connectors will want to flow together, flux will keep that from happening

backlight problem.

It is a defective LED panel, or a defective T-CON board, although you get a "NEW T-CON", it may be a defective one.

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electro-medical.blogspot.com/
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

most likely the main board, BUT not a guarantee. one of the ways Vizio keeps the cost low is by high integration and low parts count. with minimal daughter boards.

you have to open the back cover to check weather the screen back light need replacement. usually if the lamp is almost black in color it needs replacement. the backlight is covered with metal shield installed at the upper portion and lower portion of the panel of the tv.

There are only two boards. Master - 6632L-0470A REV 1.3 and Slave - 6632L-0471A Rev 1.3