I picked up a used 7880 really cheap, and I've been working on getting all the colors to print. Initially when I ran a test print I had missing squares on black, cyan, and yellow and just a few squares printed on magenta. I installed a new yellow and magenta cartridge and ran a power clean. Black, cyan and yellow are all fine now, but magenta has completely dropped out. I tried the windex paper towel under the head trick and noticed that I get magenta ink coming out on the towel, but still not on the test print. Any ideas? I'm thinking about buying a vivid magenta cleaning cartridge and printing just that color (anyone have a link to a file that will allow me to do this?). Any other ideas?