Hi @brokentvmatt ,
Seems like you have a backlight problem.
This could be either faulty LED strips or since you have replaced the power board, the mainboard telling the power board not to turn on the backlights for some reason.
Without a schematic (I can’t find one) to know where to check voltage signals between the mainboard and power board and as the audio is working and you can “see” video, to me it points to the problem being either the mainboard or the backlights.
Since you have the TV dis-assembled, consider getting a [https://www.ebay.com.au/itm/272579548329|backlight tester] (supplier example only) and connecting it to the disconnected LED power cable, (assuming it is connected to the power board) to test the backlights, independent of the TV being powered on.
If all the backlights turn on, then it’s looking like a mainboard problem