Brother HL-L5100DN User Manual page 296

Make sure you put the toner cartridge in correctly or it may separate from the drum unit.
8. Clean the corona wire inside the drum unit by gently sliding the green tab from left to right and right to left
several times.
Be sure to return the tab to the Home position (a). The arrow on the tab must be aligned with the arrow on
the drum unit. If it is not, printed pages may have a vertical stripe.
9. Install the toner cartridge and drum unit assembly back into the machine.
10. Close the front cover of the machine.
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