Tektronix Phaser 550 Service Manual page 227

B
Test Prints
Faded, pale prints
The imaging unit is old or has been exposed to too much room
light. Replace the imaging unit.
The image density sensors are not properly measuring the
amount of toner transferred to the accumulator belt. Clean or
replace the sensors.
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 drum instead of being
"erased" by the laser beam, thereby retarding toner transfer from
the toner cartridges. Replace the laser scanner.
Dark, vertical streaks and smears on the entire page
This is usually due to the accumulator belt toner waste bin being
filled and spilling out on the belt. The spilled toner is then being
transferred to the print. Most prominent in the middle of the print
and in the yellow band. A defective cleaning blade could also
cause this. In either case, replacing the imaging unit should fix
the problem.
Service Manual B-5