Brother QL 570 - P-Touch B/W Direct Thermal Printer, Service Manual

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(2) Media position detect sensor circuit
When performing printing and FEED motion through the process described in subsection
“2.3.4 (2) Media feed motor driver circuit”, the CPU reads the sensor value to detect the
medium position. The CPU receives the voltage of the media position detect sensor
(reflective photo sensor) sent through CN4 and input it through SENTAN (100 pin).
The CPU processes this voltage through AD conversion and inspects the print mark on the
back face of medium that stays on the sensor position.
A semi-fixed resistance (VR) for adjustment of the media position detect sensor is mounted
on the media type detect switch PCB.
Fig. 2.3-6 Media Position Detect Sensor Circuit
(3) Cover open sensor circuit
It identifies open/close of the top cover from the status of mechanical switch.
Opening the top cover, the contact of cover open sensor on SB PCB ASSY opens, and then
the signal is sent through CN8 to COVER_OPEN_SW (19 pin) of the CPU.
The CPU detects open/close of the cover from the change of voltage at 19 pin.
The CPU stops all performances if detecting cover open during printing, FEED or CUT.
Fig. 2.3-7 Cover Open Sensor Circuit