Tektronix Z740/N - Phaser 740 Color Laser Printer Service Manual page 119

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.
Faded, pale prints
The imaging unit is old or has been exposed
to too much room light. Replace the imaging
unit.
If printing is weak on paper only, the printer
may be printing in transparency mode.
Check to see if paper was picked from a
transparency tray or if the multi-purpose tray
is set for Transparency.
Check to see if the Color Calibration menu is
set to print lighter.
The high-voltage board is not outputting
sufficient voltage to the second bias transfer
roller, causing poor transfer of toner to
paper. Likewise, low voltage to the toner
cartridge will cause insufficient transfer of
toner to the photoconductive belt.
The beam from the laser scanner is weak
and is not properly exposing the
photoconductive belt. Poor laser exposure
results in the negative charges remaining on
the photoconductive belt instead of being
"erased" by the laser beam, thereby
retarding toner transfer from the toner
cartridges. Replace the laser scanner.
108 Phaser 740 Color Printer