Printer: Brother MFC-3420C Prints only Black and Yellow?Not knowing the exact mechanics of your printer, it's a safe guess that the print heads (not the ink cartridges) for blue and red are clogged or damaged. In many printers these are installed separately. They can become clogged or dried out if you let the ink get too low or run without ink for extended periods of time. If it was me, I would try to remove the heads and soak them in ink solvent overnight and try to clean them before replacing them.
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