Canon NP6621 Service Manual

Also see for NP6621: Service manual Service handbook

Contents

3–43OPERATIONS AND TIMINGCOPYRIGHT © 1998 CANON INC. CANON NP6621 REV.0 FEB. 1998 PRINTED IN JAPAN (IMPRIME AU JAPON)2. Turning ON/OFF the Transfer RollerBiasThe TFWON signal is generated under thecontrol of the microprocessor on the compositepower supply PCB, thereby turning ON thesecondary side of the transfer transformer (T5) andapplying a DC bias to the transfer roller.Table 3-301 shows combinations of signalsused to determine the transfer roller bias.Transfer biasoutputCleaningbias outputReferencebias output(ATVC)TREVON*OFFONOFFTFWON*ONOFFONTFWPWMONOFFOFFTable 3-3013. Controlling the Transfer BiasConstant VoltageThe microprocessor on the composite powersupply PCB reads the TFWS (analog signal) fromthe constant voltage control circuit while the transferDC bias is being generated and changes the dutyratio so that the application voltage remains constant,thereby controlling the TFWPWM signal.4. Correcting the Transfer Bias VoltageLevel (ATVC control)To compensate for changes in the transferefficiency caused by changes in the environment ordeterioration of the transfer roller, the machineautomatically corrects the application voltage levelof the transfer bias.During initial rotation after the Copy Start key ispressed, a constant current (-10 μA) is sent to thetransfer roller. The microprocessor on the compositepower supply PCB reads the transfer rollerapplication voltage from the constant control circuit,and the result is sent to the microprocessor (Q301)on the DC controller, which in turn determines thevoltage to be applied to the transfer roller.This control mechanism is executed once duringinitial rotation after the Copy Start key is pressed;therefore, the application voltage can never changeduring continuous copying.5. Current Limiter Circuit (transfer bias)If changes in the environment or the like causesan overcurrent to flow to the secondary side of thetransformer (T5) while the transfer bias is beinggenerated, the current limiter circuit starts control tomake sure that no current greater than 50 μA flows.6. Current Limiter Circuit (cleaning bias)If changes in the environment or the like causesan overcurrent to flow to the secondary side of thetransformer (T5) while the cleaning bias is beinggenerated, the current limiter circuit starts control tomake sure that no current greater than 10 μA flows.Download service manual and resetter printer at http://printer1.blogspot.com