Panasonic UF-890 Service Manual page 241

6.2.9 SNS PC Board
Each sensor consists of an LED and phototransistor. When documents are placed on the ADF tray or are
moving, a shutter in the document sensor closes. The light path from the LED is blocked turning the
phototransistor "OFF", and the output voltage from the sensor becomes a "High" level. With no document
on the ADF tray, the shutter opens the light path, and output from the sensor is kept at a "Low" level.
Operation of the RP Sensor is opposite to the ADF Sensor. When the leading edge of the document
reaches the RP Sensor, the shutter opens and the output voltage becomes a "Low" level. Then, the shutter
closes and the output becomes a "High" level when the lagging edge of the document clears the RP
Sensor. The Tx Door Sensor operation is the same as the ADF Sensor, the output from the sensor is kept at
a "Low" level when the door is closed and becomes a "High" level when the Tx Door is opened.
+24V
Transmitter
Door
Sensor
Read Point
Sensor
B4 Width
Sensor
Document
Sensor
Shutter
A
PC2
K
nSDOOR
nBPNT
Shutter
A
PC4
K
nB4
Shutter
A
PC3
K
GND
SNS PC Board
5V
nA4
Shutter
A
PC3
K
GND
+5V
+5V
GND
+5V
GND
GND
FCB PC Board
+5V
GND
241
S-CPU
(IC150)
MPU