Sensors - Brother FAX100 Service Manual

2.3 Sensors

This equipment has two photosensors and four mechanical sensors as described below.
Photosensors
• Document front sensor which detects a presence of documents.
• Document rear sensor which detects the leading and trailing edges of pages to tell the
control circuitry when the leading edge of a new page has reached the starting position
and when the scan for that page is over.
These two photosensors are located on the main PCB. They are of a reflection type consist-
ing of a light-emitting diode and a light-receiving transistor. Each of them has an actuator
separately arranged (see the next page). If an actuator is activated, its white end will come
to the path of light issued from the light-emitting diode and reflect its light. The moment the
reflected light enters the light-receiving transistor, the sensor signals the detection.
Mechanical sensors
• PE (paper empty) sensor which detects whether the recording paper is present.
• Cover sensor which detects whether the recording paper cover is closed.
• Cutter sensor which detects the home position of the upper rotary blade of the automatic
cutter.
• Hook switch sensor which detects whether the handset is placed on the handset mount.
These four sensors are located on the NCU PCB. Each of them has an actuator separately
arranged (see the next page). If an actuator is activated, its lower end pushes down the le-
ver provided on the corresponding sensor so that the sensor signals the detection.
Cutter sensor
Hook switch
sensor
Cover sensor
NCU PCB
SW3
SW1
SW4
SW2
Main PCB
PH1 PH2
Document rear sensor
Document front sensor
III – 4
(Rear)
PE sensor
Approx.
0.7 mm
Light-
emitting
diode
Power supply PCB
Path of
actuator's end
Glass
Light-
receiving
transistor