Brother International MFC 8890DW Service Manual - Page 61

When the new toner detection switch detects that the toner cartridge is replaced with a new one, the developing bias voltage is initialized at the same time. The toner used for the printer has a property that print density is light first and gradually darker in the course of usage. The developing bias controls the toner property so that the print density is constant from first to last. Toner property Actual control [Density] [Voltage] Print density [Density] [Voltage] Print density Bias voltage Bias voltage [Used toner amount] [Used toner amount] To obtain a print result of a constant density all the time, the printer counts the number of print pages immediately after the toner cartridge is replaced and changes the bias voltage according to the accumulated number of prints with the toner cartridge. The bias voltage is changed with the steps described below: (1) When the new toner sensor detects that the toner cartridge is replaced with a new (full) one, the developing bias is set to 400V (initialized). (2) After that, the bias voltage is stepped down according to the number of prints. Ultimately, the bias voltage is 300V. Corresponding counter, Setting value Counter of toner cartridge changes Page counter for each toner cartridge Coverage for each toner cartridge Developing bias voltage Operation +1 Reset (0) Reset (0) Reset (Initial setting) 2-23 Confidential