Use a step ladder to access the garage door opener s power cord and motor unit.
How ro replace garage door chain.
To do this put some lubricant on a piece of rag this use the rag to wipe the chain.
If the chain on your garage door is rusty you need to apply lubricant into it to loosen the corrosion.
This should give you room to replace the chain drive module.
Position a work table near the area under your motor unit to hold the garage door opener.
Remove the chain and cable assembly.
Pull out the idler pulley bolt and slide the idler pulley out of the rail window.
Disengage the garage door from the opener by pulling down on the emergency pull cord to release the door trolley from the opener carriage.
The top two only need to be loosened when you take out the bottom screw the cover will slide down.
Press the wall control button or remote so that the opener completes its close.
Documenting how i repaired the garage door.
Disconnect the trolley threaded shaft from the chain by removing the master link clip on spring master link cap and master link bar.
I am not a professional.
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.
Pull the chain cable out of the rail window.
You can just let the cover hang by the wires plugged into it.
Remove the chain and cable assembly.
There are three phillips screws holding on the garage door opener back cover.