Home Automation - bounce back

I have installed an old, and i do mean old Stanley Garage Door Opener on a steel insulated door. Goes up and down ok, remote works fine. However when door closes, it will reverse cycle and re-open again. Now--do the springs have to be backed off, is there too much weight and force on the door when it touches the bottom of travel ? There seem to be two sensitivity controls on the underside of the unit, however they do nothing. Haven't taken the shroud off yet, however am contemplating it. Any ideas. This unit is in good shape and i'd hate to junk it. Also what slack should there be in the chain ? I believe the is way too much now. Tks. Rewind

Normally when this happens it is an indication that the door is traveling too far in the down direction. It hits the floor and the safety reverses it to the open position. You need to adjust the down limit. Have no idea where the adjustment is on an old old Stanley.

And just a note...you probably won't be able to find parts for Stanleys, expensive if you do. They were never really made by Stanley, it was just a licensing thing with 2 different companies...now long out of business.

I think there are a couple of sites that have manuals for Stanleys, but that was on my old PC, can't find the info now.