This is a very rare occurrence, but can happen.  If the anti-skating control know wants to rotate more than 180 degrees and will turn completely around, the most likely culprit is a problem with the screw holding the knob in place.  If the screw has vibrated completely loose, it may even rattle inside. It is a Philips-head,  #4 X 1/4" screw.  So, you must either tighten it a bit or find it and replace it.  To do this you must get inside of the turntable.  Here are some steps to follow:

1) Lay the turntable on a soft surface, such as a pillow, sponge rubber sheet, or carpet.

2) Remove the 9 Philips-head screws that hold on the bottom cover.

3) Locate the anti-skating control bottom.










 4) The screw in question is the silvery item in the center of the black plastic piece that has the coil spring attached.  If that screw has become excessively loose, the plastic piece can also become so loose that it will not engage its stop.

    A. The calibrated anti-skating knob on the top fits into the bottom piece with a keyway.  When the two pieces are fitted together, top to bottom, the keyway can engage in only one orientation.  A loose screw can cause this to occur.

    B. Before tightening the screw, press the top portion to the bottom portion and rotate the top portion till the two "lock" together.  The two pieces  will snap together and lock in unison. 

    C. It is now only necessary to tight the screw a bit.  It does not require a lot of force.   If you tighten too much, the anti-skating knob will be difficult to rotate.  If you tighten it further you can strip the threads.  So be careful as to not strip anything.

5) Replace the cover and you are finished.