This page from Nikon Europe site is preserved here to complement Dirty scanner optics article.

4. The image has streaks or lines running along the image. Why?

General Advice

(Coolscan only) This is usually caused by the presence of dirt on the optical path inside the scanner. A careful jet of compressed air may remove dust from the mechanism (be careful not to hold a can-type container upside-down as this will result in a jet of fluid entering the scanner and possibly damaging it): However, this should not be seen as a permanent cure and the scanner should be returned to your authorised Nikon service centre for cleaning according to factory procedure.
Note that built-in scanners can be particularly susceptible to dust and dirt accumulation due to the computer's cooling fan sucking air in though the scanner slide feed hole. Your Nikon service centre will be able to perform a factory-standard cleaning to return a dirty scanner to full specification.
Dirt and marks on a flatbed scanner glass may be cleaned with a lint-free cloth and standard household glass cleaner, taking care that no liquid is introduced into the body of the scanner.

The eight-bit resolution limit of the Coolscan LS-20 scanner can result in contours between different colours in deep shadows being visible on certain images.

Quick Troubleshooting Guide

  1. Streaks, stripes or lines along the scan direction.
    Dirt on optics which cannot be removed by user cleaning as described above.
    Contact your Nikon authorised service centre.
  2. Streaks, stripes or lines across the scan direction
    Intermittent connection  between scanner circuit and sensor or other electronic problem.
    Contact your Nikon authorised service centre.
  3. Lines running in diagonals, image sheared (sliced and skewed)
    SCSI problem.
    Check SCSI cabling and other SCSI devices, update SCSI drivers or change your SCSI card.

©Nikon circa 2003