I recently got an error message on my 7740 that said: Problem with Supply System - replaced depleted cartridge (cyan). BUT I had just replaced my cartridges at the first of the year and have printed very little...just enough to keep printer working properly. Just before the error message it said my cartridges were 1/2 full.
...so I replaced the cyan cartridges and after the printer did its maintenance cycle it said my yellow cartridge needed replacing.
I have no confidence that if I replace all cartridges that the printer will work since it had been printing just fine until I got the first error message. What's going one?