Is any test file I can print and tell which one is the problem?
In order to check the status of the printheads you need to print the "Nozzle Health" plot:
1) in the "HP Internal Print Server" software, select "Printer >> Printhead Cleaning >> Verify Printhead Status" . Here you press the Print" button.
2) You print the "Nozzle Health" plot. You will have two rows of plot areas. In the row below, you will have a column corresponding to each color used by the printer (K, C, M, Y, LC, LM).
3)The first two columns of the row from below(colors K,C) correspond to printheads K-C. If there are a lot nozzles missing in Pen2 (D1...D6)(upper side of the first two columns), then the affected printhead is the upper K-C printhead (the first K-C printhead).If there are a lot nozzles missing in Pen3 (D1...D6)(lower side of the first two columns), then the affected printhead is the lower K-C printhead (second K-C printhead).
I hope this information helps