In the printer its self. You will see a transparent strip running along the back of the printer and also a white strip that attaches to the printer cartridge carriage. Get a damp piece of tissue and clean those. Be very gentle with the transparent strip as if you pull hard on it, it will snap and the printer is completely broke. Over time ink residue will get on to them and effect the print quality. Try that and if that doesn't work let me know and I will think of something else to try.