Why is my power dead again on F8500 Plasma? Help!

I own a 60” Samsung PN60F8500 plasma and after 7 years the power died (no indicator light or clicks). I heard 80% of the time it’s related to the power board, so I found one on eBay that came from a working tv (same model) and swapped it in. Bingo! The power was restored and everthing perfect again. Then 4 days later, the power suddenly died again. So either I got a crappy board to replace it with, or there’s another problem under the hood that’s affecting power. Besides the power board what could it be? I’m getting a new multimeter tomorrow and then I can check out some things but I’m a novice overall and trying to find my way, and I’m wondering why changing out the power board worked, but then failed again. Any advice or input is greatly appreciated. I’m trying to save this tv since I love it so much, and I’m trying my best not to take it to someone to prevent spending money on a tv that might not be justified to save in the end.