My M75-c1 takes 20 minutes to turn on.

My M75-C1 takes 20 plus minutes to turn on. Based on internet help I replaced all three power boards thinking it's a bad capacitor. The screen is perfect and the TV works perfect once it's running. After replacing all the power boards I did a factory reset and though all would be good. Nope, it still takes 20 plus minutes to turn on. When it was new it fired right up. Great TV but I'd like to get it back to starting right up. Any ideas?