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Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, will the POWER On/Off controls/buttons operate the TV normally (except black screen)?
Still, determine if the backlight is working as a preliminary try. If not, disconnect the inverters 1 at a time and note if there would be any change in the symptom/condition of the TV. This is a simplified test and may help point if it is an inverter issue.
Incidentally, why was the power supply board replaced please? ...are the symptoms the same with the old and the new power supply board?