says headphone jack is inserted so loud speaker does not work

My s4 says headphones are in, therefore the loud speaker does not work. I do get sound through headphones. I have removed motherboard and tried it in another fully working s4 with same results - headphones attached. I have thoroughly checked all ribbons, connections, and even removed the sim card tray so I am now completely stumped! Id really appreciate any feedback as im desperate for your advice and help. Thanks in advance, Dan