Lexmark W850n Service Manual page 177

Print defects guide
Match a set of repeating defects on a print
job to the marks on one of the vertical lines.
The line that best matches the defects on
the print job indicates which particular part
is causing the defect.
For example, the distance
between these two marks
represents a repeating
defect that occurs every
44 mm (1.73 in.), which
means the photoconductor
kit needs replacing.
Change the
transfer roller.
58.7 mm
(2.31 in.)
If the defect appears on the printed side of a single-sided print
job, change the photoconductor kit.
If the defect appears on the back, change the fuser.
Change the
photoconductor kit.
44 mm
(1.73 in.)
Change the
fuser.
78.5 mm
(3.09 in.)
94.2 mm
(3.71 in.)