Brother LX-300 Service Manual page 119

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Paper Width Detector Circuit (YCA-F sensor PCB)
This circuit detects the width of the document and determines the Y-carriage
position. It also determines the Y-carriage standby position when the power is ON
or the cover is closed.
This circuit comprises the transmissive photosensor PH1 mounted on the Paper
width detector PCB that is attached to the Y-carriage. If the Y-carriage is in its
standby position, the photosensor is not interrupted. When the main CPU output
P31 (YCA-LED) is Low, the input signal P72 (YCA-F) becomes Low.
When the Y-carriage motor rotates after the insertion of a document, the Y-carriage
moves from the standby position to cause the Actuator Y to cut off the photosensor.
Further rotation of the Y-carriage motor moves the Y-carriage to the edge of the
document, where the Actuator Y having cut off the photosensor (Y-CA sensor)
comes off the photosensor, thereby detecting the edge of the document. Also,
determines the Y-carriage (Y-cutter) position meeting the selected Auto Cut mode
status.
When the document edge is detected, the main CPU input signal P72 (YCA-F)
becomes Low. However, as P31 is normally at High-impedance status, the
photosensor (Y-CA sensor) does not operate and the main CPU input signal P72
(YCA-F) remains High, irrespective of the Y-carriage position.
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Document Detect PCB (PST sensor PCB)
This circuit detects the length of the document and determines the X-cutter position.
This circuit comprises the transmission photosensor PH1 on the PST sensor PCB.
It is mounted on the Paper eject roller unit. When a document is inserted, it
displaces the Sensor lever that was cutting the photosensor to turn ON the
photosensor PH1 and set the CPU input signal (P52) to Low status.
Fig. 5.4-4 Paper Width Detector Circuit
Fig. 5.4-5 Document Detect Circuit
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