I have an EZEE Quando II. The chain fell off its sprocket ( rear) and is tightly in place but on the axle and the front sprocket. So it leaves me able to peddle, but the chain is not engaging the wheel. The manual says there is a chain adjustment screw(?)near the frame at the rear of the bicycle. I cannot identify this screw(?) and doubt it will deal with how tight the chain is. I do not want to touch the rear axle nuts for fear of unbalancing the wheel. And while I have already marked these nuts so if I have to loosen them, I can try to restore the bike to its appropriate condition. This would be a last resort. Also, if anyone can explain why this happened, please let me know. The bike is less than one year old and has no gears to shift. Either the chain has expanded, the rear axle is loose (that is not evident by giggling it) or?