Why does my iPad 4 not function?

My brother in law's iPad 4th gen 16gigs, white does not function. One day the screen shut off. No activty when connected anywhere. It booted up in the sun. Shut down later on. Then nothing. Back in the sun, booted up. A few days of that, then shut down pemantly. I thought it was the battery. I replaced it with a new battery and still no activity. I put back the original battery and replaced the doc connecter. Still nothing.

Besides changing the logic board, I am at a loss of ideas.

Please share your thoughts.