[Sean]

The fine tuning control is a planetary drive with ball bearings. Most likely the grease has become hard and is keeping the bearings from moving freely. You could squirt some machine oil in between the course and fine tuning shafts to temporarily loosen up the grease. Really the best way to fix this is by disassembling the tuning drive to clean it up and re-lube the parts. I did this on my 16X code 125 that had the same problem.