NH 658 knife dropping early

Hi, I'm new to posting on Hay Talk, but have used the forums as a resource for years.  I recently picked up a New Holland 658 at an auction.  Trying to get her up and going, picks up the hay well and starts the bale as it should, but at about 45" or so, the knife drops down (set to net wrap at 60").  So once the bale reaches full size the actuator will not fully extend, and wrapping does not start.  If I manually pull up the knife, the bale will wrap, but the knife does not fall and cut the wrap.  I have to release the bale, cut the wrap with a pocket knife, reset everything and go again.   Any thoughts to what the problem may be?  It has done this every time so far.  I am much more familiar with the JD wrapping system (JD 458 & 459), so the NH system is a bit new to me, not sure where to start.   Thanks for the help. 

NH 658 knife dropping early