No power, no standby light - standby power is present

I have a 65x900f that will not power on using either the power button or the remote. I have confirmed that standby power is present on the power supply board where the cable leads to the main board. I have also confirmed that the power makes its way to the main board connector. One thing I have noticed that is strange is that the power_on pin on the power supply board constantly reads 3.5V regardless of whether the switch is being pressed or not.

When the main board is connected to the power supply board, 12V is available to the LED driver board, but when the main board is unplugged no 12V is present at the connector from the power supply to the driver board.

I have scoured the internet for any documents relating to this model but have found nothing. Does anyone have experience working on a 900f?