Xerox WorkCentre 480cx User Manual page 258

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Examine the test pattern. The example below shows a test pattern of all
nozzles functioning correctly on the color and black print cartridges.
Compare the diagonal same-color lines at the top and bottom of the test
pattern. Look for a break in the diagonal lines; a broken line shows any
clogged nozzles.
If the bottom line shows improvement, rerun this test. If improvement
continues, rerun the test. If all nozzles are not printing after running the
test three times, continue with step 5.
8-10 Maintenance