Every time you install a new Brother DR-520 Drum you must manually reset the drum counter using the following instructions.
After installing the new drum leave the front door of the printer open
FOR DCP AND MFC PRINTERS:
Press the [Clear/Back] button.
The LCD screen will show
Press [1] to reset the drum counter
The LCD screen will display
"Accepted"
You may now close the printer door and your printer drum counter is set to 100%
FOR HL PRINTERS:
Press the Blue [Go] button until all the lights light up then release the button.
Close the door and your drum life counter is reset to 100%.