If you look at the solder points for the controller socket, do any of them look cracked or damaged? You might just go through and re-solder them all, just for good measure. It's not uncommon on the Duo and Duo-R(X)'s to see control pad sockets that need re-soldering, though I don't think I've ever seen it on a TG-16, one that has been abused is very likely to need it.