HP Color LaserJet 8500 Service Manual - Page 152

Transfer drum cleaning block This block follows two steps to clean the transfer drum. Even though most of the toner is transferred to the paper during secondary transfer, some toner particles remain on the transfer drum surface. This residual toner on the transfer drum is returned to the imaging drum, where it will be moved to the waste toner case. 9. Cleaning roller charging Bias is applied to the cleaning roller so that the residual toner on the transfer drum surface is charged positive. The cleaning roller is usually separated from the transfer drum. However, the cleaning roller can be brought into contact with the transfer drum by the cleaning roller press cam which is activated by the cleaning roller press solenoid (SL1). When contact is made, positive bias is applied to the cleaning roller to charge the toner on the transfer drum surface positive. After the charging is complete, the bias is turned off and the cleaning roller press cam separates the cleaning roller from the transfer drum. After printing is complete, negative bias is applied to the cleaning roller to remove the residual toner. Figure 33. Cleaning roller charging 150 Chapter 5 - Theory of operation EN