HP Designjet T3500 Production eMFP - Manual (Page 245)

You can also see some banding in patterns 4, 9, 10, and 11, indicating that the printheads need to be cleaned.
You can launch printhead cleaning from the front panel by pressing , then Image-quality maintenance
> Clean printhead.
Streaks
Looking at patterns 1, 2, 3, 9 and 16, you may find vertical streaks as in the examples shown below, if the
printer’s printheads are not working correctly. Replacing the printhead for the color showing the streaks may
solve the problem.
Grain
Looking at patterns 1, 2, and 3, you may find problems in the printer’s paper advance or the printheads that
cause visible grain in area fills. The following examples show this defect: original on the left, printed image
on the right.
ENWW Visual check for errors while printing the diagnostic sheet 235