Canon NP1550 Service Manual

Also see for NP1550: Service manual

I OPERATIONS AND TIMING!F. Document DensityMeasurement System1. OutlineThere is an automatic density adjustment(AE) system which adjusts the DCcomponent of the developing bias to suit thedensity of the original. If the density of theoriginal is more or less uniform, the AEfunction varies the DC component of thedeveloping bias to suit the density of theoriginal, so that copies of the correct densitywill be made.2. OperationThe scanner moves forward approxi-mately 70mm past the leading edge of theoriginal and stops momentarily. Thescanning lamp goes ON for approximatelyone second, the image density is read by theAE sensor, and the sensor output isinterpreted by the DC controller. The DCcontroller then adjusts the DC component ofthe developing bias accordingly.3. Reading the Output of the AESensorThe AE sensor consists of a photodiode(Q702) and an operational amplifier (Q701).If the strength of light striking the photodiodeis high, the output voltage (AE) of theamplifier will be small. If the amount of lightis small, the output voltage will be large.The DC controller reads the output at acertain time after the zero-cross signal(ZXDP) is received from the DC powersupply.The data representing the adjusted AEreference/slope values are written toEEPROM when 'CD' or 'CI' is used in theservice mode.For reference: B6sizeApprox. A is the position of the AE sensorAPProx -25mm25mmFigure 3-23AE sensor PCB DC controller PCBCOPYRIGHT© 1992 CANON INC.Figure 3-24CANON NP-15S0 REV.0 JAN. 1992 PRINTED IN JAPAN (IMPRIME AU JAPON] 3-25