Tektronix Z740/N - Phaser 740 Color Laser Printer Service Manual page 121

Single white spot appear in the same
place on the print
This indicates a bad spot has developed on
the imaging unit's photoconductive belt
which will not transfer toner. The imaging
unit must be replaced. If the spot appears to
migrate vertically from print to print then the
defect is on the imaging unit's accumulator
belt. In either case the imaging unit must be
replaced.
Contamination of one color by another
This is most noticeable on solid primary fills.
This is caused by a defective
photoconductive cleaning blade. The blade
is not scraping off all of the untransferred
toner from the previous pass of the
photoconductive belt to the accumulator belt
prior to the next toner's transfer to the
photoconductive belt. Replacing the
imaging unit corrects this problem.
Rarely, a sheet of paper can become folded
and jam in the imaging unit, smudging the
image.
110 Phaser 740 Color Printer