I'm guessing you want to get into TV repair. The power cycling is hard on the set and will eventually lead to more bad boards. Try the power board then the main board. Without the service manual, bench gear and a background in electronics this is all you can do.
There are some that are upset about this but here we are. Not everyone is going to repair their car today.
I have an older Samsung TV that I use in my basement. Lately when I turn the tv on it doesn't come on on the first try. It cycles a couple times with a black screen and a loud screeching noise. After some trail and error I realized if I unplug my cable from the HDMI ports the tv turns on but once I plug it back in the tv turns off and does the cycling thing again. How do I fix this?