This machine uses four photoconductor units (PCDUs) in tandem (one PCDU for each color YMCK).
The PCDU is composed of the drum unit [D], the development unit [A], the drum cleaning unit [C], and the charge roller unit [B]. Each color PCDU can be drawn out of the machine.
In MP C6503/C8003, the parts in each color PCDU are exactly the same (a drum unit [D], a development unit [A], a drum cleaning unit [C], and a charge roller unit [B]) in order to minimize the cost of parts. In Pro C5200S/C5210S, the parts in the development unit [A] for K are different from the parts for YMC.