Canon PC940 Service Manual - Page 55

CHAPTER 3 EXPOSURE SYSTEM 2. Relationship between Scanner Sensor and Signal Scanner sensor PS1(scanner home position sensor) Signal SCHP Scanner Forward Reverse Description • Provides a means of reference for determining forward movement distance. • Stops the scanner moving in reverse in 0.1 sec. Table 3-102 3. Basic Sequence of Operations (scanner) Power switch Copy Start key ON ON STBY INTR SCFW SCRV SCFW SCRV LSTR STBY Scanner home position sensor (PS1) Pre-registration roller paper sensor (Q751) Scanner I II I Scanning lamp(LA1) Forward Reverse I : Scanner home position detection II : Lens home position detection Figure 3-105 The microprocessor on the DC controller PCB controls the forward movement distance of the scanner with reference to the falling edge of the scanner home position signal. The forward movement distance of the scanner varies according to the length of copy paper and reproduction ratio. If the ratio is less than 130%, the scanner is moved forward as if for A4 (297 mm); if it is 130% or more, the scanner is moved forward as if for LTR (279 mm). For descriptions on how length is detected, see p. 5-10. COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON) 3-5