Quote from Robert on October 3, 2017, 2:43 pm

1. Open the front cover.
2. Grab the handle of the exhausted drum unit and carefully pull towards you, in order to take the exhausted component out of the printer.
3. Remove the toner cartridge from the exhausted drum unit by pushing down the green lock lever and pulling the cartridge upwards, and then unpack the new drum unit.
4. Insert the toner cartridge into the drum unit until it clicks into place, and the green lock lever is automatically elevated/raised.
5. Locate the green cleaning tab (on the top side of the new drum unit) and slide it to the end of the cleaning channel.
6. Slide the green cleaning tab back to its original position, and then repeat the previous and the current steps 3-4 times, in order to be optimally cleaned the primary corona wire of the new drum unit.
7. Make sure that the green cleaning tab is back to its original position, and then insert the new drum unit along with the attached toner cartridge into the printer.
8. Reset the drum unit counter by pressing the [Clear/Back] button and confirming the new drum unit installation by pressing the [1] button.
9. Wait for the following message ''Accepted'' to appear on the control LCD, and then close the front cover of your Brother MFC-7840W Multifunction Printer.