Brother HL-5130 Service Manual page 95

2.3.3 Cassette sensor / Paper empty sensor (HL-5140/5150D/5170DN)
Detect if the paper tray is installed. They also detect if there is paper in the paper tray.
Cassette sensor PCB ASSY
2.3.4 Paper eject sensor
Detects if paper is ejected from the fixing unit.
Eject sensor PCB ASSY
Fig. 3-38
Fixing unit
Fig. 3-39
HL-5130/5140/5150D/5170DN SERVICE MANUAL
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Paper empty sensor
Cassette sensor