Xerox Phaser 8400 Service Manual page 263

Test Print Examples (Continued)
Gray Fill, Dot Size Uniformity
This print is made up of a 66% black fill. It
reveals variations in the ink-drop-spread
caused by thermal variations, transfix roller
pressure variations, or drum oiling variations.
Look for:
1. Large area of differences in the density
across the width of the page. (A slight
variation is normal.) Look for a lighter
vertical band, about 1/3 the width of the
page, running the length of the page. Also,
look for small, light spots, or irregular white
lines, vertically aligned with each other, in
the print every 125 mm (5.0 in.).
2. Also, look for ink on the top and bottom
margin of the page, or ink on the back of
the page. This pattern is sensitive to the
density variations in the paper it is printed
on. Use a high-quality grade of printer
paper; otherwise, the print appears
mottled.
Causes:
1. Use the diagnostics to check the printhead and drum for correct thermal regulation. Ensure
the drum fan is running properly. A vertical band, 1/3 of a page wide, running the length of
the page, is caused by a stuck heating plate in the paper preheater. Run the Control Panel
cleaning procedure
preheater and may free the stuck heating plate. Additionally, you may manually force a thick
sheet of paper (65 to 80 lb.) through the paper preheater to jar the plate free. Light spots
that repeat every 11.63 cm (4.58 in.) down the length of the page are caused by a defective
transfix roller. The roller has a soft spot that is not pushing the ink into the paper as well as
the rest of the roller. If you observe variations in the glossiness of the print, replace the
maintenance kit.
2. If there is ink on the top and bottom margin of the page or ink on the back of the page, it
may be caused by the roller remaining down during the print. You may hear an unusual
noise if the Transfix Roller stays down and rubs against the drum. Inspect the Drive Train
and ensure that it self-homes between prints. The drive train is in its home position when
the two 1.5 mm holes found on the clear plastic cover align axially with corresponding holes
in the gear. Another way to verify that the drive train is in its home position is to verify that
the two small leaf springs from the clear plastic cover are seated correctly in their
corresponding gear detent slots. Inspect the perimeter of the cam lobes for surface defects
and check to see that the angular orientations of the cams match. Inspect the transfix load
arm return springs. Verify that the maintenance kit returns home between prints. Inspect
the cam shaft surfaces for damage. If all of these items are working correctly, replace the
process drive module.
Manuf. Five Duplex GSF
This print is used by Manufacturing and
Engineering.
Print-Quality Troubleshooting
Clean Print Smears, which raises the temperature of the paper
Light band Light band
Uneven fill Uneven fill Uneven fill
Should see Should see Should see
even fill even fill even fill
left to right left to right left to right
s8500-05
5-37