We've repaired and sold a lot of Y-Main boards for this TV in the past , but when we moved to our current location in the middle of 2014 we broke our own unit and haven't been able to repair and sell those boards anymore.
So naturally we assumed the problem was in the Y-Main, but it wasn't.
The TV was totally dead and that pointed towards the power supply, which is PSPF501A101A :
We tested the board in-place (in the TV) and it was lacking 5V standby.
All fuses tested out good and we had to take it out for further investigation.
All power components tested good and there were no visibly bad electrolytic capacitors.
We ended up finding the rectifier for the standby voltage output being shorted.
This is the diode DB864 that sits on the secondary winding of the small transformer producing the standby voltage:
On the above picture the diode is already taken out of the board, sorry.
It was SB5H100, which is a 100V / 5A rectifier.
It doesn't need 100V on the secondary side of the standby and frankly I am surprised it needs 5A, but if they used it then probably there was a good reason for it.
We didn't have a through-hole 5A/100V diode, so we used an SMD one that we put on the other side of the board:
Hope this helps someone save $100 or so for a replacement board.