Thank you for your reply! So this chip resides inside the printhead and replacing it would likely fix the problem? How come the lighter shades of magenta are printed on the testsheet, do these use different nozzles?
When I currently print with my Canon MP630, color images all look green-blueish with a small horizontal stripe of correct coloration about every cm.
When printing the nozzle test page, I see that the darker magenta stripe is only half it's width, indicating that magenta does not print there...