The biggest hardware problem I see with (older) BlackBerries is the TrackBall fails to scroll. It fails to scroll, because over time, it fills up with oil and grime from your fingers. Now, unlike a computer keyboard, you can’t stick it in a dishwasher. Doing that would certainly break your warranty and won’t fix the problem.
(Dirty trackball to clean trackball)
So the solution until now, has been either return it to the seller (if under warranty), or get it repaired at some cost.
I stumbled across William Clangford’s YouTube video, and his fix works very well. If you have a TrackBall which isn’t scrolling anymore, it’s worth the 49 second investment to watch the video.