On a TV parts sight I found the 3 boards used in h
TCL Roku 4K 65"
$35 plus $10 for express shipping = >$50 DIY repair.
Same boards people are reselling individually for about $90 on Walmart and Amazon marketplace, so keep that in mind.
A year or so ago, replaced the power board and worked like a charm.. now I'm having a no picture, blank screen with back lights working. Saw the boot up screen flash on then go back to blank after reset button on back for 20 seconds. Trying the controller sequence first, it's initiated. If no cigar after 10 minutes (and maybe another attempt or two) I've luckily saved the other 2 boards from the kit (network board and main board) so what can hurt at this stage? Took under an hour swapping out the power boards... and that's with me being very careful and methodical with esd strap etc.
If I don't follow up, then the sequence or board swap worked.. I'll add a new comment if zero effect after efforts. Likely, at this stage, can get a bigger, better one for less than what I paid for this puppy originally (though, dang, nice to not have to buy a new TV right before Christmas)
Cheers! Love this site.