The Radio Information Board

I have a tk-3160 and the knob will only go to channel 5 without forcing it. Is there a mechanical stop under there that the dealer or prior owner installed? If so how do you remove it?

Thanks in advance

shouldn't there be a stopper. but to check, you gonna have to remove the case. to do this:
1. unscrew the 2 chassis screws
2. pull out on/off knob
3. remove front case assembly
4. pull out ch knob, should see a white plastic spacer under the ch knob.

hope this helps.