Whenever you replace the drum unit in a Brother MFC-7420 laser printer, you must reset the drum counter. Otherwise, your printer will continue to show a "replace drum" error and you won't be able to print! Here's how you do it:

How to Reset Drum Counter

1. With the front cover open, press CLEAR.
2. The printer will display, "Replace drum?" Press 1 to confirm you are installing a new drum.
3. After the display shows "Accepted," close the front cover.

That's it. Enjoy your new drum!

Guaranteed Supplies for Brother MFC-7240 from Print.Save.Repeat:

TN-450 Toner Cartridge
DR-420 Drum Unit