Yellow and magenta are on the same head and protected by the same fuse. If they just dropped out completely out of the blue, that's probably the issue. Check your head cables to make sure they aren't dirty or damaged. If they are, replace them. Then replace the fuse. It's a 1.6 amp fuse and, depending on the age of the machine, it's user replaceable but might need to be soldered if it's an older version.