TV clicks but doesn't power on. Main Board or Power Board?

Symptoms:

• When the TV is plugged in a relay clicks continually in this pattern: click - 10 second pause - click - 60 second pause . It continues to do this over and over again.
• When the power button is pushed on the remote or the tv: The relay clicks - white indicator LED comes on for 15 seconds or so - LED turns off - 1 second pause - relay clicks. The TV never actually powers on.

What I’ve tried:

• I downloaded the service manual, and the triage section only covers when you get a red blinking error code, or if there is no power whatsoever. Neither of which apply here.
• I followed the service manual instructions for diagnosing the PSU board anyway. It seemed fine, but I’m also an extreme novice.
• If I disconnect the main board from the power board, there are no relay clicks

The buddy who owned this TV told me he took it to a repair shop and they said it was a backlight. That doesn’t make sense to me. I’m thinking maybe main board or PSU board. But I’m not sure where to go from here.

For reference here is the power board