Brother DR-400 Drum Unit - Why does the message CHANGE DRUM SOON continue to appear on the display after I replaced the drum?

This message would continue to appear if the drum counter was not reset when you replaced the drum. To reset the drum follow the instructions listed below:

1. Open the front cover.
2. Press the CLEAR key.
3. Press 1 to reset.
4. Close the front cover, pressing firmly on each side until they click into place.

If the message continues to appear on the display, unplug the power cord, wait approximately 30 seconds and then plug it back in.

If the message still appears, reset the drum and toner:

1 Open the front cover (below the paper ejection tray) by pulling the taps on the left and right side of the unit towards you.
2. Lift the drum unit slightly and pull it out.
3. Remove the toner cartridge from the drum holding down the lock lever (purple tab) on the right side of the drum unit and lift the toner out.
4. Reset the toner into the drum (be sure it clicks into place).
5. Reset drum unit in MFC.
6. Close the front cover, pressing firmly on each side until the cover clicks into place.

Reset the counter:

1.Open the front cover.
2. Press the CLEAR key.
3.Press 1 to reset.
4. Close the cover, pressing firmly on each side until they click into place.