Craftsman 1/2 HP chain-drive

Model No. 139.53985D

I have identical openers on both garage doors. One is working fine, the other is opening and closing with no remote or wall button input. It will cycle open and then close within about 10-20 seconds later. It will cycle again within a few minutes. It has occassionally opened about 1/3 and cycled closed from there, but usually goes through entire cycle. I have to unplug it to keep it down and then plug it back in to open it.

Any help is greatly appreciated.