check the 90 degree cable with a multimeter for continuity and resistance. if you see any abnormality then the cable might be suspect. Also verify the cable ends, the contacts might not be 100% lined up. It also wouldn't hurt to check your connector on the logic board to make sure the contacts are straight and in the correct spot.
I've once purchased a few cheap cables and had a 50% failure rate due to the ends. after straightening the contacts the cables were working. I quickly returned them all once new cables came in. My clients were wondering why i was asking for their computers back a week later.
Also check the original cable to see if it's damaged as that might help you locate the fault on the new cable.