Brother HL-3400CN Series - Manual (Page 192)

CHAPTER 5 MAINTENANCE
5-35
5. Make sure that the Metal Lock Plate at the front of the tray unit is in
the Release position.
Fig. 5-40 Metal Plate Position
6. Check the two alignment pins on the Lower Tray Unit. Use two
people to lift the printer and place it onto the Lower Tray Unit. Be
sure to use the handholds located at the bottom four corners of the
printer. Check to ensure that the pins align correctly into the printer.
Fig. 5-41 Place the Printer on the Lower Tray Unit