Tim, i hope you are handy with a soldering iron. I would start looking at the capacitors on your power board. It sounds like you have a few that might need replacing. It is also possible that a mosfet on your board has failed. You can download the service manual from here Check your power board and see if your caps are either leaking (sticky oil like substance on the PCB) or if the tops are bulging. Those are the once to replace. Parts are available at places like this if you want to replace the board. Your caps can be purchased inexpensively at places like Mouser.com and Digikey.com Of course, make sure that you read and follow the safety precaution when and if you decide to work on your TV. Hope this helps, good Luck
I have the same problem and decided to replace the whole power board; filter board and TNPA4774AG SS Board... still not working..
then using my oscilloscope i measured the frequency, and noticed that it was the RF board, N7AE or 1AA4B1ON22900..
All these parts are available from Shop Jimmy.com
I compared prices with a TV repair shop and there was a massive saving if you do it yourself. ( If you know how to unplug a power socket, then you can do this yourself )
TV SERVICE GUY $695 plus labor
Shop Jimmy.com $250, FREE SHIPPING.