Canon PC740 Service Manual - Page 62
Controlling, Primary, Charging, Roller
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OPERATIONS AND TIMING'' D. Controlling the Primary Charging Roller Bias 1. Outline Figure 3-206 shows the circuit that con- trols the application voltage of the primary charging roller, and the circuit has the following functions: • turns on and off the DC/AC bias. • controls the DC bias to a constant volt- age. • controls the AC bias to a constant volt- age. • switches the DC bias voltage level. The primary charging roller is given both DC and AC biases so as to maintain the surface potential of the photosensitive drum to a specific value. The DC bias is switched according to whether or not a copy image is being formed. Reference: DC component: -400/-625V AC component: 1700 Vpp to 3000 Vpp AC power supply Transformer T101 Transformer T508 Amplifier Primary charging roller Photosensitive drum E 2 cu 0 0 0 0 Oscillation/ amplitude control circuit cC C) 7) O Z C0 n0O :5 < O a Microprocessor /\ Composite power supply PCB 3 - 22 Microprocessor Figure 3-306 DC controller PCB COPYRIGHT © 1994 CANONINC. CANON PC720174011500 REY.0 AUG.1994 PRINTEDIN JAPAN(IMPRIMEAUJAPAN)
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