HP Designjet T3500 Production eMFP - Manual (Page 218)

And here is an example of the same printhead in a bad state:
Corrective action
1. Clean the printhead if necessary (see Clean the printhead on page 240 ). Then reprint the Image
Diagnostics Print to see whether the problem has been solved.
2. If the problem remains, clean the printhead again, and reprint the Image Diagnostics Print to see
whether the problem has been solved.
3. If the problem still remains, replace the printhead (see Handling ink cartridges and printhead
on page 144 ), or contact HP Support (see Contact Support on page 253 ).
If you still have a problem
If you still experience print-quality problems after applying the advice in this chapter, here are some further
things that you can do:
208 Chapter 20 Troubleshooting print-quality issues ENWW