They build things to a price these days.
In my experience, in most cases repairs are just not worth it.
Estimating your TV was around 13 000 Baht over a year ago.
You could probably get the same one for under 10 000 now and another
brand probably cheaper.
So unless your tech can repair it for around 3000 Baht, you're better off getting another one.
My experience with Tv's in Thailand is they have lasted generally about 4 years.
I've had most brands, Sony, Panasonic, Samsung and LG.