Hi, the problem you have is probably the rotary selector under the knob, there is no belt to another component. there is a small pcb. with the rotary selector on it.however this is now not avaliable from Panasonic. However if you contact your local service centre they may be able to find a replacement component to do the job,as these Alpha wheels as they are called are used by a large number of makes.
Best of luck John
P.S. I had this problem some years ago, I will try and find some details if I can.