You will need to open up the TV from the back to do what it takes to diagnose this.
Takes tons of screws to do so...make sure to put them all in the same bag, or, if you're very novice, to even mark which goes where.
You may need to lay the TV down and take the stand off it. I am not sure how the stand goes on this particular one, some allow the cover to be taken off with the stand on and others require to take out the stand first.
One benefit of having it laid down is that it's harder to lose screws somewhere between the boards. It's a benefit you will value only after you lose a screw between the boards :-)
Once you take the back cover off you will want to disconnect the Y-Main board from the power board.
The Y-Main board is the large board with two solid rows of heat sinks at the LEFT side of the TV looking from the back.
At its top right there is a connector with several relatively thick cables that go to a board in the middle of the TV.
That's the power board.
So your first goal is to disconnect that cable and then try to turn the TV on again. You may need to raise it up or you can actually leave it lying down, it's all the same.
What matters is if it will come and stay on as opposed to blinking 3 times.
There are two possibilities here:
if it starts up and stays on then you have bad Y-Main/buffer boards and are looking at about $220-$230 in repairs/replacements (at today's prices) to fix it properly, which is repair the Y-Main board and replace the two buffer boards. This is the most common scenario and it has variations in either direction.
The second option - if the TV still does the same - is that the power board is bad. This is the second most common scenario and of course it also has variations. if the power board has a problem it is good to look at it after the TV shuts off. It should have a green LED on its own blinking an error code as well.
And , well, there's the third scenario where something else is bad; that's really rare, but a full troubleshooting from here on would require more time and money.
Feel free to contact us for repair or additional troubleshooting info.
Hope this helps!www.coppelltvrepair.com