I had the same problem, trackball wouldn't scroll down. I stumbled upon this video in a thread over at XDA. It sounds stupid, but worked like a charm. My trackball works like new, and it is very simple. The video is actually for a blackberry trackball, but it worked for my eris.
YouTube - How to Fix a Stuck Blackberry Trackball
Try it, can't hurt and might save the trouble of getting a replacement.
YouTube - How to Fix a Stuck Blackberry Trackball
Try it, can't hurt and might save the trouble of getting a replacement.
