6. Post charging AC and DC bias are applied to the post charging unit to add the appropriate bias to the toner that is on the transfer drum and to increase the efficiency of the secondary transfer. The post charging unit is turned on during the yellow toner primary transfer as well as after the entire image is formed. During the yellow toner transfer, the negative charge is decreased. A negative bias is applied for the black toner transfer to increase the efficiency of the secondary transfer (the transfer of the toner from the transfer drum to the paper). Figure 30. Post charging EN Image formation 147