My VIzio E550i-B2 TV has no picture and no sound. Do I need a new power supply board?

First thing is test power supply voltages as the power board on this model has had some issues. You need to test the 12 Volt supply for correct voltage and ripple as cap failure is somewhat common. Don't worry about the 5 volt supply. If the voltage looks good you have a bad main board and that board will be hard to find and expensive, over $100 in most cases. As strange as it sounds a bad inferred sensor board will also make no sound but I can't say I've head of that issue being intermittent.

Hello Brian, if you have changed the power supply board and still have no image, then some of the LEDs that are responsible for illuminating the screen are wrong, to solve the problem, you should replace all the LED strips, because if only change the ones that have one or two damaged Leds, the other strips, they could fail you soon and you would have the same problem again
I sent you a video of [ShopJimmy.com] that shows you how to replace the LED strips, in another Vizio TV model of 55 "
I hope you can solve the problem of your TV Vizio
Greetings Franco Dosil

Hola Brian, si has cambiado la placa de la fuente de alimentaci?n y todav?a no tienes imagen, entonces est?n mal algunos de los Leds que se encargan de iluminar la pantalla, para resolver el problema, deber?as reemplazar todas las tiras de Leds, porque si solo cambias las que tengan uno o dos Leds da?ados, las otras tiras, podr?an fallarte pronto y volver?as a tener el mismo problema
Te env?o un v?deo de [ShopJimmy.com] que te muestra como reemplazar las tiras de Leds, en otro modelo de TV Vizio de 55"
Espero puedas resolver el problema de tu TV Vizio
Saludos Franco Dosil

Without some voltage readings its only a guess but it sounds like a power supply issue

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://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.

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://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.

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/
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....

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/
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.

The led is what makes the picture try replacing that it it's the only one you didn't change out

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://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.