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Note what you've done.
1st, IF the YMAIN board was unscrewed and Powered on....that board is likely blown. If the Xmain was unscrewed, those do seem to survive better.
2nd, the RIBBON cable to the YMAIN...if that was disconnected and the TV powered up, the Ymain is destroyed too.
The Ymain is the most susceptible part of your TV set. It should always be screwed in and the ribbon cable must never be disconnected when powered up. The logic board's 5 second blink tells me that's the most likely issue you're dealing with. You see those buffer boards (single/dual buffer??) connected to the YMain? Did you also have those unscrewed/disconnected from the Ymain? BOTH should be connected to the Ymain when powered up if you have 2 of them. If one is connected, and the other isn't...it'll blow the connected one.
So, those are the absolute must-have rules regarding Samsung plasma TVs and testing them. If you've broken any of the above rules, you will need to replace the Ymain and the buffer boards to get the TV to come alive.
Questions? I'll be home this evening if you need more information.
You had to apply power to the board when you turned it on for the above information to be true too. I guess you have to replace the boards that were unscrewed.
Alright, replace the Ymain and buffers connected to it.
Yes, the X main is ok. No the Ymain /buffers are responsible for priming the panel so the picture appears on the TV panel.
I've never seen those go bad.
"replace the Ymain and buffers connected to it."
Did you replace the buffers too?
That's not good. If they blew that fast, the ONLY thing that can eat those buffers and Ymain would have to be a short on the plasma panel.