Service manual

2.3.7 Sensor Circuits
The CPU detects conditions of the following sensors: home position (HP) sensor, release sensors 1 and 2,
platen gap (PG) sensor, rear and front paper end (PE) sensors, paper width (PW) sensor.
Two types of sensors are used in this printer. Release sensors 1 and 2, the PG sensors, and the front PE sensor
are momentary switches. Pages 2-3 and 2-4 describe the relationship between release and PG sensor
operation and actual print operation.
The HP sensor, rear PE sensor, and PW sensor are photo diode switches. The HP sensor detects CR home
position when the photo diode rays are cut off by the printhead. The rear PE sensor detects that paper has
been loaded when the photo diode rays are cut off by the sensor plate, which is included in the rear PE
sensor. The PW sensor, used for paper width measurement and paper loading positioning, detects the paper
edge by comparing the voltage it measures with a standard voltage that was measured during the power on
sequence.
Additionally, as mentioned on the page 2-24, the +35 V line and head temperatures are monitored to set the
pulse length of the head driver signal.
CPU
P36
P40
AN2
P53
P27
+5V
PG Sensor
+5V
+5V
HP Sensor
+5V
+5V
Rear PE
Sensor
+5V
Front PE
Sensor
+5V
+5V
PW Sensor
61
76
75
68
70
Release
Sensor 1
67
68
Gate
Array
R2
R1
Release
Sensor 2
Figure 2-38 Sensor Circuit
LQ-2070 Service Manual Operating Principles
Rev.A 2-27