Canon PC980 Service Manual - Page 103

CHAPTER 4 IMAGE FORMATION SYSTEM 2. Operations a. Turning On and Off the Transfer Bias The transfer bias applied to the transfer charging roller is turned on and off by the serial communication signal from the DC controller PCB. When the transfer bias ON signal (serial signal) is generated by the DC controller PCB, the microprocessor (Q900) on the composite power supply PCB generates the high-voltage transformer control signal (CLK32K), transfer DC bias ON signal (T_FW_ON), and transfer DC bias control signal (T_FW_DRV), thereby applying the transfer bias to the transfer charging roller. Negative transfer bias ON Positive transfer bias ON (cleaning bias) Transfer bias OFF ATVC Transfer bias ON signal (serial communication) bit2 bit3 1 0 1 1 0 0 0 1 T-FW_ON signal 1 1 0 1 T_REV_ON* signal 1 0 1 1 Table 4-103 Relationship between Transfer Bias Output and Signals b. Controlling the Transfer Bias to a Specific Voltage The transfer bias applied to the transfer charging roller is controlled to a specific level by the microprocessor (Q900) on the composite power supply PCB. When a transfer bias is generated, the microprocessor (Q900) on the composite power supply PCB checks the transfer bias voltage detection signal (T_FEEDBACK), compares it against the reference value, and varies the transfer DC bias control signal (T_FW_DRV) according to the difference to ensure that the transfer bias remains a specific level at all times. Reference: The level of transfer bias applied to the transfer roller during a copying run is between -7.5 and -3.0 kV. COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON) 4-9