> has anyone got any suggestions to solve this?
Take Cari's advice, call canon. The mp750 is new enough that you
should be under warranty, and the scan to pdf function would make it
handy to scan your test sheets. Printheads are like lightbulbs with a
limited life.
If you are in the UK (noting the pound marker" electroversal is the
offical distributer
http://www.electroversal.com/
If you are out of warranty, try anyway, then someback for advice
regarding agressive cleaning techniques. As discovered recently Canon
is rather liberal regarding their warranty period.