LG 55UB8500 Won’t Turn On

This TV wouldn’t turn on but the front LED would blink once when the power button was pressed.  Typically if you have a front LED (indicating you have standby voltage) and the TV doesn’t power up, it is a main board issue.  I probed the PS_ON and DRV_ON signals on the main connector and didn’t detect a DRV_ON signal so I ordered a replacement main board.  When I installed the replacement board, it behaved exactly the same way.  I ordered a used power supply board next and it was pretty inexpensive at under $20 USD shipped.  When I plugged it in, I noticed LEDs light up on the main board which weren’t on before and the TV powered up.

I should have done a more comprehensive job of checking power supply voltages before concluding the main board was bad.  Luckily the seller takes returns so I will ship it back and take the hit on shipping charges.

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