3. Turning On and Off the AC Component of the Development BiasThe microprocessor (Q512) on the composite power supply PCB generates theACBIAS signal (pulse signal) under the control of the microprocessor master (Q301) onthe DC controller PCB. In response to the signal, the development bias AC componentgenerating transformer (T301) turns on to add the AC component of the developmentbias to the DC component for application.• application frequency 2400 Hz (approx.)• application voltage 1300 Vp-p (approx.)4. Controlling the Voltage Level of the DC Component of the Development BiasThe copier modifies the voltage level of the DC component of the development biasbased on the following factors:• setting of the Copy Density key• output of the AE sensor• position of the Copy Density Correction knob (VR302)The copier controls so that the voltage of the DC component of the development biasvaries between –80 and –560 V (in actual terms) by varying the output of the BPWMsignal.To ompensate increases in thelight potential (VL ) caused by deterioration of thephotosensitive drum, the copier is equipped with a copy density correction volume. Youmay operate the volume (VR302) on the DC controller PCB to adjust the potential of theDC bias for any increase in V L, thereby freeing the copies of fogging.Figure 4-205COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-26(to lighter) (to darker)VR302Developing bias(DC component)-500-400-100DarkerMediumLighter(darker) 5Copy density(lighter)
