I have a Canon S520 printer. One day, text documents printed in black started to fade by the time the printer got near the bottom of a page. It was as though there was a partial blockage to the cavity feeding the individual inkjets. As long as I printed something that did not call for too much black ink at a time, the print was fine. I tried a new cartridge and cleaning cycles to no avail. I tried the air blast cleaning method and a lot of ink did come out. The bad news is that the printer then stopped printing black completely. I tried a few of the other suggested cleaning techniques but nothing helped. I was on the verge of shelling out for a new printhead. With nothing to loose I tried the following: I washed just about all the ink out of an empty black cartridge. Then, I filled the cartridge with windex. I put the cartridge in the printer and after about 5 days it started depositing windex on the paper. I put a normal black cartridge in and after the windex got washed out, it started working just fine. A word of caution: If you are going to try this, I would suggest that you make a test pattern of narrow vertical black lines. Try running a cleaning cycle then print the test pattern and look for stripes of dampness on the paper. You do not want to try printing too much continuosly because the inkjet elements may overheat. If you don't see anything on the paper, keep trying once a day. I see no reason why this would not work on the color jets as well.