I have an unusual problem in that if I print a page of black text using the 'Fast' print configuration, then I get a poor print on every 6th line of text. If I print using one of the 'Quality' settings the the print is fine. It only happens when I print using the black ink. The three colours are fine. I use compatible cartridges. I've tried cleaning the nozzles, but this doesn't make any difference. I've changed the black cartridge 3 times, because the printer randomly decided that it didn't recognise it. I'm wondering if there is a problem with the firmware / hardware that controls the black ink.
Any thoughts would be much appreciated.