Replace the Imaging Unit. It is possible that one of the developer unit to be without developer material.
I'm having the same problem. Did you ever find a solution?
It could be the drum, take a look at the drum for the particular color and see if there are any visible defects.
Have a look at THIS guide.
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Thanks for your input but these cardridges does not come with a seal
I have this printer. Did Magenta get gradually lighter? It could be that the seal wasnt taken off of the cartridge when you replaced it. This would cause it to gradually get lighter till eventually no Magenta. You may need a new xerographic module.
I need help, tried every thing possible but Magenta is not priniting - All red colors are printing out in Yelllow. I'm using WorkCentre 6505, the printer is sensing all the colors, Magenta color cartridge is at 60% but all red/ orange/ pink colors in documents are printed in yelllow. I even changed the cartridge with a new one, the printer read it at 100%, but still not printing the red colors. That is not only for user documents but even for the printer build-in demo page. It print out in yellow (including the Xerox logo). Again, I replaced all the cartrides with new ones and the same problem remain with red colors.
I always use genuine Xerox toner cartridges. Cannot understand whats going on. Please help