The cost/benefit analysis would lead you to replace, unfortunately. Unless you happen to have the correct parts on hand and can narrow it down, you are SOL. Even with parts you still are no longer under warranty and it can quite easily fail again IME. YMMV.
Luckily, the same $700 now can get you an HDTV with better PQ and features.
Need help with troubleshooting this smart 3D tv probably less than 6 years old, seldom watched. when turning on with remote, the tv turns on to light up the touch controls at the very bottom of the screen but have black screen and no sound. pushing remote voluime control and channel control the tv power button blinks like it is responding. I suspect this is a common issue with LG LED TVs but have found very little specific helpful information to troubleshoot and fix on the internet. anyone with similar issues with their LG TV would be helpful. suspect a faulty power supply board, no visual evidence of damaged capacitors --they all look normal, no back lighting visible. Menu will not come on either...puzzled.it was a $700 TV.