Paper will not feed in

Question

I have a Geha Primo 1800 Shredder. The motor turns the shredder teeth in reverse manually with the rocker switch but will not autofeed the paper in. I am assuming one of three things might be wrong. The sensor is broke or blocked, the rocker switch is not working on the feed in side or something is disconnected inside. I lost the owners manual and do not know how to remove the top cover to get inside to check it out. Any advise on repair would be greatly appreciated. Thanks