Funny, went to check and my rewind knob was missing. Be sure to cinch that down tight or it might fall off. Retraced my steps, went back where I was walking today and found the knob.
Originally Posted by Chan Tran
Now for your problem. With the lens off, inspect the bar that presses the pin when the shutter is activated. S3 does not have a meter switch, been a while since I had an S3V. The bar might be different than my Spotmatic F. On mine the bar is bent back on left and right sides so you can remove the lens or attach it and it won't shear the pin as you screw the lens on.
Check the shape of the bar and make sure it does not catch on anything. Maybe it's a little bent and hits the inside of the lens mount instead of moving forward freely all the way?
Good luck solving the problem.