Replaced new video chip still scrambled screen?

Ok so I have been reballing chips for a while now, I use high end equipment and repair a lot of macbooks. I received a macbook pro A1150 with disorted video. I first reflowed it, same problem, reballed it, same thing, tried another chip from another board, same problem, tried a new chip and still same problem. I even tried to replace the intel graphic chip in the middle of the cpu and ati chip and still same thing. And yes I have tried to hook it up to a few different lcd screens. I also have an A1226 board that has white screen and same thing I have replaced most of the components. I am trying to diagnose what the problem can be. If someone can share some light over here. I am not sure if the cpu can cause this or south bridge?