Developed a problem with my Prince NEOS 1000 tonight. Went to string my racquet and for some reason I was unable to turn the tension knob. It seems to be stuck at 0 lbs. My machine is only about 2 yrs old and I probably string only around 6x/month. After every use I make sure to dial the tension knob back down to 0 to save wear on the spring. Took the cover off the tension head and nothing seems to be broken, just that the knob won't turn now? Anyone ever have this happen?