Thanks for checking. Unfortunately at this point I have limited service documentation available, and your ability to do any definitive diagnostic electrical testing is limited, so we really cannot proceed any further from here.
If I had to take a guess, I'd expect you've got a bad Y board, however based on the age of the tv there are no longer any parts available, no matter which board it is.
If you wanted to send your Y board in for repairs, you can do so here: http://bit.ly/1NCzeat
Personally, I wouldn't consider it worth any further investment for an offbrand 10 year old 720p tv. Even if you fix this, the tv is well past its expected service life and would not be expected to have the other components last much longer anyway. If it were me, I'd be much more inclined to invest my money in a new tv, when you can get a brand new LED tv with twice the resolution, updated features, and a fresh warranty, in the $300 range.
Depending how you'd like to proceed though, I can recommend replacement options, or I can opt out and see if another expert here would be willing to work with you further on this. We are really at the limit of what can be done without you being able to detailed testing with a meter though.
Best regards, ***** ***** for the news,