The front standby LED was on and would turn off and on when the power button was pressed but there was no backlight and no sound.
Probing the power supply connector, PWR_ON and DRV_ON signals were being sent from the main board but there were no voltages on the LED connector or secondary voltages like 12V. Checking the big main filter capacitor across the leads, the PFC circuit was not boosting up to the expected 390VDC. Power supply part number is EAY62512701.
Posts on badcaps suggested checking D607, C603, Q601 and Q602. I found D607 shorted while the other parts testing good. I ordered a replacement for MUR460AX (600V, 4A axial leaded diode) from Digkey part #MUR460GOS-ND
Normally, the diode in this application is a TO-220 package which can be mounted on a heatsink for better heat dissipation. When I installed the new part, I floated it above the board to allow for more airflow around it.
With D607 replaced, the TV powered up with backlight coming on. The interior of the TV had black dust on the power supply board and back of the TV and I confirmed that the owner was a heavy smoker. There was also some smoke residue on the bottom corners of the TV.