Have sound but no picture. Has an ever so faint flicker of light on the screen every 3 seconds

SOURCE: samsung HP-R4262- has sound but no picture...

YOU SHOULD HAVE REPLACED THE Y-MAIN BOARD AT THE SAME TIME, NOW DON'T TURN IT BACK ON UNTIL YOU REPLACE THE Y-MAIN OR IT COULD TAKE OUT THE NEW Y-MAIN

SOURCE: how hard it is to replace by yourself main board Samsung LN-T4065

You need to do some more diagnosing of the problem. If you get sound and change channels take a bright flashlight and place it again the screen. Look for an image around the edge of the flashlight.
If you see an image that means the LCD controller board (TCON) is probably good.

The problem is probably one of three causes;
1) Inverter board is bad
2) CCFT (cold cathode fluorescent light) are bad.
3) Power to the inverter board is bad. You can also check the connectors.

SOURCE: Samsunb 4051: TV screen turns off sound stays on.

Most likely this set has an "integrated" inverter, as most samsungs do--and this DOES sound like an inverter problem. Make SURE thought, there are no more bad "10 volt" caps on the power supply...ALL of them need to be replaced no matter HOW they look.

SOURCE: I hav a Samsung 50''

Hello

First of all, please replace or at least have checked out the Ymain and Yupper and Ylower boards. In many cases if one blows they all blow.

Changing the boards is not difficult if you know what you are doing. However I suppose a brain surgeon might say the same thing. If you are comfortable with repair electronics then no, its not difficult at all.

http://blog.coppelltvrepair.com/2010/03/how-to-identify-burned-buffer-boards.html

That will give you some pics and a place to start.

Best of luck

SOURCE: I have no picture but

Do you still have your old board,if you do put it back in and see if it does like the New Board.
In the mean time I need to do some checking on this model ,Samsung has some of these sets
that you have to replace 3 boards and On one model their is a 680uf 25v Capacitor that goes bad.
Have you looked all the boards over to make sure you have no swollen or vented on Top capacitors? Check your pico fuses also they will look like resistors but will be green or yellow.
1amp - 7amp pico fuses.The person who told you that the buffer boards where probably ok do they do TV Repair Daily? Or do Samsung warranty work? Ps it is possiable that you got a defective board just because they are new/rebuilt means nothing when it comes to repair, Ive had to ship a many of boards back due to being DOA dead on arrival? I paid $279.00 for a Deflection board that was No Good that really got me,Plus they losted my SSB board and that was another nightmare.