Unfortunately I don't have a ph meter, so my best guess is one or more of these problems: nutrient lockout, ph imbalance or nutrient burn.
The first 3 photos are from an Auto Northern Light and the last 2 are from an Auto Jack Herer.
A ph meter is an absolute must have. Without knowing the ph its all a giant gamble, you have no way of tracking ph shift, and thus have no way to accurately adjust ph. You can get a good meter on amazon for about 45 bucks. Happy growing.