Brother 8840DN - B/W Laser - All-in-One User Manual page 193

5
Remove the protective cover.
6
Insert the new toner cartridge in the drum unit until it clicks into
place. If you put it in properly, the lock lever will lift automatically.
Toner Cartridge
7
Clean the primary corona wire inside the drum unit by gently
sliding the blue tab from right to left several times. Return the
blue tab to the Home position (▼) before reinstalling the drum
unit and toner cartridge assembly.
Home Position(▼)
TROUBLESHOOTING AND ROUTINE MAINTENANCE 12 - 32
Drum Unit
Tab
Corona Wire