Tektronix Phaser 550 Service Manual page 226

B
Test Prints
Large, random light smudges
Spots such as those illustrated are caused by fingerprints on the
photoconductive or accumulator belt. Often, the smudges will
gradually fade with additional printing. Alternately, the imaging
unit will have to be replaced.
Finger prints can be removed by applying some toner (any color)
to the fingerprints and rubbing lightly with a cotton-tipped swab.
Don't remove the toner. The printer will remove the toner with its
the cleaning blade. Remember not to expose the imaging unit to
ambient light for more then a minute.
One or more dark vertical line in all colors
This can often be traced to a dirty scorotron charger (main
charger) corona wire. Contamination (dust or toner) interferes
with the flow of electrons from the wire to the photoconductive
drum. Toner is then transferred to the area of low electron charge
and consequently to the accumulator belt and finally the print.
Remove the scorotron charger from the imaging unit and clean
the charger's corona wire. Replace the scorotron charger, if
necessary. If this fails to correct the problem, replace the imaging
unit.
Service Manual B-4