If you are not experienced with TV repair, purchasing a replacement motherboard (which comes with software pre-installed) is often safer and cheaper than potentially damaging the mainboard with incorrect flashing.
In an era of planned obsolescence, the act of downloading and flashing firmware is a quiet rebellion. Manufacturers often prefer consumers to buy a new unit rather than provide the .bin or .pkg files needed for a fix. By seeking out the TP.SK518D.PC821 Tp.sk518d.pc821 Software Download