Brother HL-5050 - Manual (Page 109)

5 - 11 ROUTINE MAINTENANCE
6
Put the drum unit assembly in the printer.
Make sure that the printer is turned on, the front cover is open and the Status LED is red.
Figure 5-20
7
Reset the drum counter. See the instructions supplied with the new drum unit.
Caution
■ The Drum LED indication does not disappear until you reset the drum counter.
■ Do not reset the drum counter when you replace only the toner cartridge.
8
Close the front cover.
9
Make sure that the Drum LED is now off.