Canon CanoScan 9900F Service Manual page 26

CHAPTER 2
2. FAU Lamp Lighting Circuit
Figure 2-7 is a FAU Lamp Lighting Circuit diagram.
When the host computer sends a film scanning command, ASIC turns off the scanning lamp
lighting signal (LAMP) and simultaneously turns on FAU lamp lighting signal (XPA) to light
the FAU lamp.
Light of the FAU lamp is converted into a flat light source by a light guide plate. The light
is diffused by the1st diffusive film, the luminous intensity enhancement film and the 2nd
diffusive film. Light transmitted the transparent plate all has the same luminous intensity as
a result. Light transmits a film and is focused on the CCD in the scanning unit.
The FAU lamp also has a lamp OFF function for energy saving.
3. Infrared LED Lighting Circuit
When the host computer sends a command to light an IR LED, ASIC turns on IRLED signal
to light the IR LED.
The IR LED light is converted into a flat light source by a light guide plate. Light transmits
a film via the1st diffusive film, the luminous intensity enhancement film, the 2nd diffusive
film and the transparent plate.
Inverter PCB
Scanner
Host
Computer
2 - 8
FAU
FAU Lamp
IRLED
IRLED
XPA
ASIC
Main PCB
Figure 2-7
COPYRIGHT 2003 CANON INC. CANOSCAN 9900F REV.0 FEB. 2003 PRINTED IN JAPAN (IMPRIME AU JAPON)
Reflective Film
Light Guide Plate
1st Diffusive Film
Brightness
Enhancement Film
2nd Diffusive Film
Transparent Plate
Scanning Unit