Jim:

The adjustments are in there! It's been 6 years or so since I worked
on an SP-600, but I remember that those adjustments were hard to
locate. If you have an otoscope (the thing the doctor uses to look in
your ears) you can spot the adjustments with ease. Taking off the
bottom cover may provide a bit more light. I don't recall having any
problems with stuck or frozen adjustments. Persistance will pay off!
Best Regards,

Ed