Lynx 455 Garage Door Openner - caught in loop

[abcnck]

Hi, I have a Lynx 455 automatic garage door opener. When I opened it last night it got to the top of the run and immediately started down again. It got about 2 feet into the down cycle and started up again. It just kept going up and down in the same pattern until I pulled the plug. It is quite old and does not have any laser eyes or safeties. Any suggestions? Thanks Alex

[Ken]

The first thing I would do is to disconnect the opener from the door and see if the door moves freely. All openers (that I know of) reverse if they encounter what they think is excessive resistance.