The "Change Drum Soon" warning message is one the common errors that users come across on Brother laser printers. If your Brother MFC-7420 is displaying this error message, you should in fact replace the drum unit with Part No. DR350. Consumables like drum unit and toner cartridge requires regular replacement. Don't worry; your printer isn't defective nor has serious damages. You can continue to print as long as print output is acceptable; however, you should have a replacement kit handy to avoid interruptions. This troubleshoot guide will also work with the similar Brother Laser Printer Models: HL-2040, HL- 2070N, MFC-7220, MFC-7225, MFC-7820N.
Step 1 - Turn off the machine, unplug it from the power outlet and let it cool down for 5-10 mins.
Step 2 - Open the toner cartridge access door. From here, you'll see the drum and toner cartridge assembled into single unit. Remove the whole thing out of the machine by gently pulling it out.
Step 3 - Remove the toner cartridge out of the old drum unit. Just press down the "lock lever" to release the cartridge. (Place the used drum unit and toner cartridge in the bag and box for recycling.)
Step 4 - Unpack the replacement DR350 drum unit and remove the protective plastic shield. Run the corona wire back and forth 2-3 times to remove any excess toner out of the drum. See the picture below for your reference.
* Do not touch the green drum roller on the drum unit. Fingerprints on it can cause print quality issues.
Step 5 - Install the toner cartridge to the new replacement drum unit. Slide down the cartridge into the drum unit until you hear it locked into place.
Step 6 - Put the whole thing back into the machine. Just insert the drum and toner cartridge assembly back into its original place and make sure it is locked into place.
Once you're done replacing the drum unit, you need to reset the drum counter manually by completing these steps:
Step 1 - Turn on the machine and open the toner cartridge access door.
Step 2 - While open, press the "Options" button on the machine.
Step 3 - The LCD panel will then display "Replace Drum?" Press "1" for Yes.
Step 4 - Wait for the machine to finish the resetting process. Close the toner cartridge access door, print a test page and you're good to go.