Do I replace the backlight itself, or the controller board or the main board in the TV?

Try a Hard Reset first.

Note: To perform a hard reset on a Vizio Smart TV, you will need to use the remote.

1. Unplug your router.
2. Press the menu button on your Vizio remote.
3. Navigate to System on the menu and select OK.
4. Select Reset & Admin and select OK.
5. Select Reset TV to Factory Defaults and select OK.

More items...
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Mar 19, 2022

How to Hard Factory Reset a Vizio Smart TV - Alphr

Hard Reset VIZIO TV E60-C3, how to - HardReset.info

https://www.hardreset.info > devices > vizio-e60-c3
In the first place, you need to turn on your VIZIO E60-C3 TV. · Once the TV turns on, press the Menu button on the remote. · Now the Menu should appear on the ...

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Start by unhooking the cable from the main to power board, see if you get backlights. That will tell if the backlight section is working

Was this the original problem before replacing the main board?
Maybe you have to set the new main board from maintenance menu. Sound and image comes from the main board, so i believe it has to be something about it...

good luck

You have to check all the voltages, that comes from its main power supply board, to its back light inverter board. These is one pin at the backlight inverter board; comes from the main board; which controls the back-light inverter to start and off. This voltage is generated at the main board, and send to the back-light inverter board, as control voltage. It will be best to contact any service technician. If you wish to get some details; check the site linked here.Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/

Thats the IR board. You can get the IR board along with the button assembly at the following link for your model its 15.00 just scroll down the page. It also may be the main board that has the issue if it is you can also get the main board there also its 84.00
http://tvrepairworld.com/lg__zenith_lcd__plasma_power_supply_boards

Im having similar problem and with my limited knowledge of lcd tvs and the voltages ALL being good except the pwr on or sw on voltage from the main board to the power supply which tells it to switch everything on Im guessing that something is going wrong on the main board. In the condition where it freezes it (the power on V) which switches everything on i get varied voltages such as 2.5 or 3 or (the normal 5v) and then when nothing powers up (blank screen) i read 0v on pwr on voltage but all my other voltages are corect (24v to inverter, 12 v to main board, 5v, etc.) Im guessing from researching this is that there is in improper voltage somewhere in the main board circuit. I have been unable to find it so i may order another board and post back.

Sounds like the main board as it has all control and signal processing on it.

Hello
If sound output is OK, and there is no picture, the fault is with backlight section itself. Check its backlight CCFL lamps, and backlight inverter board for fault. This is the picture of the backlight inverter board to your TV. It can ble located at the left side of the display panel. There is norepair to this bard other than repalce it with same type and number. Before replace it, check whether proper voltage comes to it from the main power regulator board.

check the inner screen connection very well

The menu button on the TV itself is bad and must be replaced ( or removed ). Alternatively the whole front button assembly can be disconnected. Just follow the wire back to the main chassis and unplug it.