of brushoff from techs is they don't want to waste your money and there's enough income from warranty to put them in luxurious retirement. Take it as a tip and move on. If you absolutely cannot buy an extended warranty for the Hitachi at this point in time (26 mos makes it improbable), sell it on craigslist for what you can get and buy a replacement set.
Most general TV service techs troubleshoot by replacing parts; they do not have factory test fixtures and diagnostic tools to accurately isolate the failure. The plethora of TV makes, models and evolving technology makes it financially impossible for them to invest in tools. They use their experience and educated guesses as to what might have failed, then replace it to see if the fix works. They won't pay to buy the trial part, you'll have to pay for it. Almost no board assembly cost less than a couple of hundred $. Add the diagnostic service fee and you are forking out $300-400 with no assurance the problem will be fixed. If the screen needs replacing, you could buy 2 new TVs for its price.