By the way, it sound to me like what you are referring to are the adjustment pots for tuning the scanners. There is one you probably don't want to touch and the other three are used to tune the scanners using the ILDA test pattern but, the problem you are describing doesn't sound like a simple tuning issue. They are "Servo Gain", "High Frequency Damping", "Low Frequency Damping" . I don't believe you want to do anything with the one labeled SI.
Here is a link to a good guide for making these adjustments:
http://lasershowparts.com/files/Arti...20Tutorial.pdf
I would tend to lean towards a bad wire or solder joint first.