I just bought a used 909 last week, and so far I love it. I've run into two problems, though, and I wanted to see if they're typical to 909s or if it's worth getting checked out (there is still time left on the warranty).
The first problem is that when I tap in the BPMs, they will fluctuate WILDLY. Say I'm playing something that is actually about 120 BPM. When I tap it in, the readout will fluctuate between, say, 120 and 250 BPM. Eventually I can get it to settle down but it takes a good two or three bars of tapping, which makes it very difficult to throw effects in quickly on the fly. I never had this problem on my EFX-1000.
The second problem is that the crossfader adjustment screen frequently pops up while I'm switching the effects button and the effects volume knob. I'm 100% positive I'm not accidentally hitting the crossfader button. It can be quite annoying if I'm trying to look at the different effects and this screen pops up. Does this happen to anyone else?