There have been several field reports of the LA500 or LA500-S missing its preset limits. When present, this issue causes the arm to stop at locations other that the programmed open or close limit location. Resetting the limits does not correct limit drift or it will reappear shortly after the limits have been reprogrammed. Limit drift can be up to one foot in some cases.
The root cause of the issue is associated with the assembly process at the time of production. Only a small quantity of LA500 and LA500-S arms produced prior to July 28, 2014, are affected.
Please confirm that all of the mechanical hardware used to mount the arm is secure and the A and B dimesions have been installed as per the manual. If you still experience this issue, please contact LiftMaster Technical Support at 800-528-2806 to obtain a Return Goods Authorization for a replacement control arm.