I have an older Overhead Door Company garage door opener. It is a chain driven model. When I push the opener button, the door will only travel a few inches and then immediately return to its prior position. There does not appear to be any adjustments available on the unit. The length of travel is controlled by plastic pieces that clamp onto the chain. When the plastic piece reaches the motor (door fully up, or door fully down) it activates a switch to shut the unit off.

There are three electric switchs on the back of the unit that are used for changing the remote control code (and presumably other activities of the opener). Unfortunately I do not have any type of users manual, and my randomly pushing switchs has not improved the performance of the door opener.

How do I adjust the travel on this unit so the door will fully open or close and remain in that position until activated again?