Was the new board still under warranty?
I don't know what is going bad in your power board, but 10 years back or so, they frequently went bad due to leaking aluminum capacitors. A part worth a whopping 87 cents. They look like a tiny beer can. Bad ones will often bulge on the top like a frozen beer can, and may ooze a yellowish paste. Mine was oozing stuff out by one of the legs (right leg in pic)
I was able to repair my TV by de-soldering the bad capacitor and replacing with a new, high quality one. That was an LG and it is still kicking 9 years later. Not a horrible repair if you can find a youtube video on how to disassemble your TV. There is some high voltage DC to be aware of that might be lingering in the old capacitor
H
View attachment 161575