I had the same issue with a customers 1520, after fiddling round with it for a bit I noticed that some of the soldered points on the back of the screen assembly weren't covered like on the original screen. These points are located to the left of the circuitry that shows through the mid frame at the top end.
Since vibration worked on the original screen, I insulated those points and hey presto! Vibration returned. Give this a shot.