Canon PC720 Service Manual - Page 65

OPERATIONS AND TIMING= 2. Turning On and Off the DC Component As soon as the Copy Start key is pressed, the microprocessor on the DC controller PCB sends the developing DC bias on signal (DVDCON) to the microprocessor on the composite power supply PCB. In response, the microprocessor on the composite power supply PCB drives the main transformer (T101) to generate a DC bias for the developing cylinder. When the developing DC bias on signal (DVDCON) from the microprocessor on the DC controller is cut, the microprocessor on the composite power supply PCB stops the drive to the main transformer (T101), thereby cutting off the DC bias. 3. Turning the AC Component On and Off About 3.5 sec after the Copy Start key is pressed, the microprocessor on the DC controller PCB sends the developing AC bias on signal (DVACON) to the microprocessor on the composite power supply PCB. The microprocessor on the composite power supply sends the AC bias oscillation signal (ACBIAS) to the amplifier, which in turn drives the transformer (T201) and generates an AC bias for the developing cylinder. The AC output of the transformer (T201) is transformed/rectified and then supplied to the static eliminator. When the developing AC bias on signal (DVACON) from the microprocessor on the DC controller PCB is cut off, the microprocessor on the composite power supply PCB stops the AC bias oscillation signal (ACBIAS) to cut off the AC bias supply. COPYRIGHT © 1994 CANON INC. CANON PC720114011501710 REVD AUG. 1994 PRINTED IN JAPAN ompnimt AU JAPON) 3 - 25