I just installed a new gear & sprocket assembly since the old drive gear was totally chewed up. The problem I'm having is that when I run the opener, the sprocket will make a clockwise cycle but will immediately do a counter-clockwise cycle in the same distance. I've done it without the chain and with the chain and it's the exact same thing either way. That is what happened initially before I changed the gear & sprocket assembly; the door was just opened 3/4 of the way and then wouldn't move at all (because of the chewed up drive gear). Now with the chain attached to the sprocket, the door moves a few inches up and then back down to where it started from. Nothing is obstructing the sensors because the lights don't blink when this happens and when I deliberately stepped into the sensor, the lights do blink. Any help/suggestions would be greatly appreciated. Thanks