When I got my 1600 recently, it was the same way. When you change record sizes, does it make a difference? Mine didn't.
Remove the lid, platter (lift up. If it seems stuck to the spindle, knock the top of the spindle with the handle end of a screwdriver), and remove the headshell, locking down the arm. Turn the unit on it's back and remove the bottom screws. The great thing about the 1600 is that the housing comes off from the top! Carefully remove it around the arm. Take the under-the-platter cover off (4 screws).
I worked the record size dial to see what it affected. It was stuck on a vertical shaft. Sprayed silicone spray carefully on that shaft and finger loosened what was on it. As mentioned, take a long q-tip (I use ones for tape recorder head cleaning. Some Radio Shacks have them), remove old grease and put new lithium grease on those paths.
You can hand turn the spindle shaft and watch stuff work. Once everything's loose, you can set where the needle hits the record and lifts off by adjustment screws on top.