I have a 50 inch Samsung Smart TV UN50EH5300 that went dead...so I replaced the voltage supply board and it came on sound but no picture.

Check the backlight if you have backlight only two things will solve the issue . The Tcon board board need to be changed. The other would be to get another main board those tow parts I mentioned will solve your issue would try the tcon board first

the voltage is ok doo you have constantly 150 v if not led blocks is bad

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

I wouldn't replace a power board before measuring to see if the voltages are there and correct....

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WHAT Plasma TV BOARD CAUSES NO PICTURE REVIEW ...

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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.

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.

Here is what to check when your TV is turned on, power light is ON, but no picture is seen or sound is heard:

1 - Be sure the component you are using (Xbox, Cable, SAT, ROKU) is turned ON.
2 - Check to be sure all cable and cords are securely connected to the TV inputs and component outputs.
3 - Make sure you are on the correct input as some TV's will show a black screen if there is nothing connected to that input.
4 - Unplug the input you are trying to use from the TV (such as an HDMI Cable) and plug it back in.
5 - Check for signs of damage on all cords and cables from the TV to all components.
6 - Make sure the TV is not in ENERGY SAVE MODE, press the button on the remote control to go back to normal mode.
7 - Unplug the TV for 10 minutes to see if there was a temporary one time issue with the TV.
8 - Disconnect the TV from power for 2 minutes, then when plugging it back in PRESS AND HOLD THE POWER BUTTON ON THE TV FOR 10 to 20 SECONDS to try and force the TV to reset.
9 - If after checking all these different issues, you may have a Faulty Power Supply Board, A Bad Capacitor on the Power Supply Board, Loose Wire Harness, or Loose Ribbon Connector in the TV itself.
10 - Most likely when a TV has the power light ON but NO PICTURE and NO SOUND, it is the Power Supply Board that has failed.

BTW, here are solutions for you to play iTunes movies on Samsung smart TV

I would verify the voltages on the power supply board first because an improper voltage to a circuit board may make that board look bad.

Tries tv unplung,replug it back like about an hour later.For the tv to do a resetting itself back to the factory setting.Tv now 50/50 the tv might work as normal again.If the tv dosen't.Tv have a dead 1 or 2 backlight buffers boards have to be replacing.These 2 long backlight buffers boards only job are to provided a tv plasma screen panel for a backlight to see the picture.Tv now the plasma screen panel have no backlight that why ur tv have only audio sound and no picture.No experience in tv repair and never done any electronic board parts replacement before.Best just call many tv shops and explain the tv situation it in and get the best quote prices for parts and labors.Best prices parts and labors should be around $400 is fair more than that as i said shops around for more tv repair shops.