The print head on my P600 tests properly, but I get what looks like violet dandruff on the underside of the brim of a black top hat. I saw a question on this site "What is my Epson SureColor P600 suddenly printing weird cyan colors?" A respondent suggested shaking the matte black cartridge even though the nozzle test was clear. Did this work? Why would it work? Thanks.
I reported a similar problem to Epson Support. Their test protocol: 1. Print test page. 2. Check for complete registration from each of eight ink cartridges. 3. If registration incomplete or absent, then clean print heads at least three times. 4. Print test page again. 5. If problem not resolved, wait 6 hours then print page again. 6. If problem still not resolved, call Epson Support for further support.