Don't see the manual for my garage door . Need to adjust how the garage door closes. Have adjusted the chain so it's close...but it still wants to go down slightly to far and it seems the saftey isn't working. The sensor should sense the concrete floor and stop. The instructions on the garage door opener also state to test the downwood force with a 2X4 board. Worried to try this until I have the manual to know how to adjust properly.