I had exactly this problem. Used s9500s are not particularly expensive and after the command wheel came away I more-or-less wrote it off. But before finally doing so I decided to see if I could fix it myself. By that time, the plastic flanged collar had gone missing, but, amazingly, the control knob was still lying around. You can follow in my footsteps and avoid some of the mistakes I made. The top case plate is held on by just two screws and some moulded plastic clips. It tucks under the flash so it’s easier to prise out with the flash flipped up. Try to do it gently, the whole assembly is connected to the rest of the camera by a single flexible connector which comes out easily but is fiddly to get back. The electronics is shielded by and mounted on two metal plates which are connected by a woven conductive cloth strip. Each is fixed by two screws. Don’t rip the cloth strip off, remove both plates together. The notched metal ring will then fall away exposing the circular spring. This may also fall away...