Tektronix Phaser 840, Service Manual

Page: 192 / 207

Service Guide 181
6: 66% Gray, 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 or transfix
roller pressure variations or drum oiling
variations.
Look for: 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 1/5 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 13.3 cm (5.25 in.).
This pattern is sensitive to the density
variations in the paper it is printed on.
Use a high-quality grade of laser printer
paper; otherwise, the print will appear
mottled.
Causes: Use the PC diagnostics to check
the printhead and drum for correct thermal
regulation. Also check the
printhead-to-drum gap. Ensure the drum
fan is running properly. A vertical band,
1/5 of a page wide, running the length of
the page, is caused by a stuck heating
plate in the paper preheater. Run the front
panel cleaning procedure
Clean Ink
Smears
which raises the temperature of
the paper preheater and may free the
stuck heating plate. Additionally, you may
manually force a thick sheet of paper (65
to 80 lbs) though the paper preheater to
jar the plate free. Light spots are caused
by a defective transfix roller with a weak,
soft spot that is not pushing the ink into
the paper as the rest of the roller does. In
this case, replace the drum/transfix unit.
Replace the drum maintenance cartridge
roller; particularly if you observe variations
in the glossiness of the print.
9923-88
Should see Should see
even fill
even fill
left to right
left to right
Should see
even fill
left to right
Light band Light band
Uneven fill Uneven fill Uneven fill