Canon iR4570 Series Service Manual page 716

preventing toner from being evenly deposited on the cylinder and, thus causing white lines.
<Field Remedy>
Replace the Developing Assembly
<Image Sample>
F-14-5
<Note>
If you remove the right door or the drum unit when replacing the fixing assembly and work with the developing
assembly inside the machine, the developing cylinder will remain exposed and become subjected to dust or other
foreign matter. For this reason, it is important to remove the developing assembly as well as the drum unit when
disassembling and assembling the image formation or fixing system. This, however, does not apply if you are simply
replacing the drum unit.