Garage Door Chain Sprocket Broke
If the chain has come apart because of the gear and sprocket then this is what you will have to replace inside the motorhead it is very common for the gear and sprocket to come apart or wear out because the gear inside the opener is made of plastic.
Garage door chain sprocket broke. If i was doing it i would charges an 85 service call plus the 2 part. It comes with the sprocket assy worm gear and the motor drive gear. Tighten the bolts on. To do this put some lubricant on a piece of rag this use the rag to wipe the chain.
Grasp the chain 1 foot from where it connects to the end of the threaded chain anchor. On some openers the chain is half wire and half cable the cable usually breaks. They do not just fall off. Pull the chain toward the garage door and hold it in position.
This is a common problem on craftsmans. Slide the pulley toward the garage door until the chain is stretched tight then move it toward the motor until the middle of the chain touches the upper side of the chain arm. Causing the same effect. The sprocket that turns the chain commonly break off and will make the chain hang down.
Garage door opener will cost you anywhere from 300 500 to replace i usually keep at least two. Garage door opener is very strong and seldom does the chain actually break. If the chain is seriously old 20 or 30 years i would probably use a new chain. If your chain is badly corroded you may need to remove the chain from the carriage assembly and soak it in lubricant for a few hours.
The plastic wheel or sprocket at the front of opener where it attaches above garage door will break and fall apart. What it sounds like is that the sprocket broke. If the chain on your garage door is rusty you need to apply lubricant into it to loosen the corrosion. In this case the cable can be replaced fixing the problem.
Roller chain rarely breaks. Disconnect power to the unit take off the cover of the unit. If a chain is hanging down from the opener then something has broken. Thread the nut s facing the door clockwise until it meets the bracket then release the chain.
Sometimes the cable will break if it is a combination chain and cable drive system. Press down on the chain with your finger. The reason the chain went off track was because the chain. You need to get a gear and sprocket kit.