A scratch on the scanning bed of a copier can cause a solid black line to appear on all copies, as the scanner cannot read the original document properly through the scratch. The scratch can also reflect light and create noise in the scanned image. The printing function is unaffected by the scratch, as it does not use the scanning bed. The technician should inspect and clean the scanning bed, and replace it if necessary. Reference:
https://partners.comptia.org/docs/default-source/resources/a-core-1-content-guide (page 16)