I think I have an answer with reason to back it up. After much searching, I finally found the Apple Technician Guide for this model at the following URL: - http://download.docslide.us/uploads/chec... A few other places offered it too, but at a price. The diagnostic method in the guide suggests the Logic board need be replaced. Via external links the guide also referenced how to test the board but the links were dead ends which presumably only work for Apple affiliated workshops with the correct credentials. Thanks for everyone's input. So now I am looking to buy the logic board.