Hitachi 55R7 weird blue splotch on screen?
 

This is a Hitachi model 55R7 4K UHD Roku smart TV and is about 5 years old. It was working just fine until a week or so before the problem. It started with one side of the screen losing definition and 'ghosting' when the picture changes. This was intermittent, and I thought was solved after I re-seated all internal cables, however it came back and ultimately resulted in a total failure somewhere. Now, when the TV is turned on, I just get a black screen with a large blue splotch that fills the entire screen within a few seconds (see attached images). The TV will turn itself off after about 15 seconds. All symptoms made me suspect the T-Con board, which I replaced, but this did not solve the issue. I'm hesitant to declare a bad LCD panel because the entire screen suddenly died, rather than only sections of it. Maybe the mainboard should be replaced? This is only $25 but perhaps someone can tell me before I order that it's not the problem. Only other thing I could think of would be the LVDS cable. (If I unplug the mainboard end of that cable, the screen goes black...plugging it back in replicates the slowly expanding blue splotch each time.)

If it turns itself off after 15 secs, I would suspect something in the PS.
Check for puffed caps, poor solder connections, etc.

I have uploaded a video to YouTube to hopefully help with this issue. See here:

https://youtu.be/Ar4M8ufI_Kk

If your screen has two ribbon cables connecting to the T-con board, try disconnecting them one at a time. If you get a "normal" left or right side picture with one cable not connected, chances are the disconnected half of the screen is causing the problem.

I tried this after first getting the problem...as I recall, the disconnected side just went all white. I'd need to pull the set apart again to confirm this, though. I tried both sides with the same result.