I wanted to add my 2c.
My 8820's trackball refused "down" too yesterday, I tried it all (alcohol, compressed-air, push&scroll in every direction and combination) and nothing helped.
Battery-pull etc. was not helpful either and it was pretty clear it was a hardware issue.
So just before I was about to get a new trackball on ebay (there are quite a few and they usually run around $14-17 with shipping) I decided to try and do a more detailed check/cleanup.
I used the "color your trackball" method published somewhere on this forum (meant for the Pearl, but very similar procedure for the 88xx based on my experience) and pulled the trackball out.
I check the 4 tiny wheels that the trackball rotates (based on the direction) and of course one of the wheels did not rotate no matter what I did with the trackball!
It was obvious it is not touching the trackball (either moved too far or there's something between the two), but I could not see any lint/dirt visible and compressed air (even when in the open) did not release anything...
So as last resort I took a tiny pin from my wife's sewing kit and pried (I know, that was a risk...) the tiny metal clip that covers the tiny wheel/cylinder that wasn't moving.
I did not remove the metal clip, I just pushed it up (further from the plastic base) a bit and BOY was I surprised (or not) to find a HUGE piece of lint (looked like a lot of jeans fiber...) stuck and compressed between the metal clip - wheel and trackball.
This entire cavity was filled with lint.
And now I realize why compressed air or alcohol did not do a thing. This thing was huge, probably accumulated in the past 3-4 months.
So after a lot of wiggle and pulling (the lint) with the sharp pin, all the lint was out, few minor blasts of compressed air released the last few fibers and the wheel started moving as designed again!
Placed the trackball back into the 8820 and all is well.
So, lesson learnt
if the basic compressed-air/alcohol doesn't fix it for you, and you want to potentially save the $14-17 to buy a new one. try the above method.
If you have questions let me know. Sorry for not taking any photos.
BTW, I just found this detailed step-by-step on PinStack (Trackball Cleaning and Disassembly w/ PICTURES - PinStack.com - BlackBerry forums
) this is very similar to what I did, a recommended bookmark!