Just replaced sprocket assembly (including worm/gear drive)on old Craftsman 1/2 hp opener (no sensors). After reassemby, opener worked fine going up, but did not go back down (only clicked). Checked limit switches, disconnected door, and manually reset limit to lower position. Again, opener rotated counterclockwise to upper limit and stopped. When pressing again, just get click. I had replaced the worm/gear in the past and did not have this problem. Prior to sprocket breaking off, opener worked well. Any ideas??? Could it be the logic board, limit switches??? What controls the 'sending' message to the motor to reverse its direction??? Don't want to invest a lot in this old opener, however did just pay for the sprocket kit. Any sugestions would be greatly appreciated. Thanks!