The only thing you need to do with a belt driven opener is to adjust the belt occasionally.
Tighten garage door belt.
The manual does not indicate how to solve this problem.
This is a very simple job to do yourself in fact all you need to do is follow this simple 6 step guide.
Brand new chamberlain garage door opener with excessive slack in belt drive.
Tighten the adjuster three full turns clockwise to add tension if the door closed and did not remain open halfway.
Loosen the adjuster three turns counterclockwise if the door raised without.
Step 1 closing the garage door before beginning use the garage door opener to close the door and fasten it.
1 close the garage door.
All you need to get started is a step ladder a 7 16 inch wrench and a flat head screwdriver.
In most cases all you have to do is adjust the opener belt of the belt drive tightening it to ensure smooth running.