Refill toner Brother MFC 7420

Open front cover, press OPTION button, on the LCD will appear a message "NEW DRUM?" ....DO NOT RESPOND....just type on the keyboard "*00" and there will appear a message "Accepted" and use it in your pleasure.

PS. in any case i blocked with paper labels the viewing windows from transparent plastic on the toner itself....

Mr. Brother, do not try to be smarter than your customer

1.open the front cover 2.press options button and then press start button
LCD does not show anything 3. press hurriedly number 00 and close
the front cover immediately. 4.your printer will resurrect. good luck

You need to reset the little white gear lever on the end of the cartridge. That is what tells the machine that the toner is empty. Unscrw the 3 screws, carefully note the current location of the white end of the gear lever and rotate it to the other extremety. Screw back together and that should sort it.

I have replaced a new brother drum, after reset it, "toner life end, replace toner cartridge" message appears. How to solve this problem in MFC-7840N ? I have replaced with a new tone.

This is the response in the FAQ section on Brother's website:
(It is focused on making sure the cartridge is installed correctly.) The web link for this information is at the bottom of this post.

1. Verify the toner cartridge is installed correctly by following the
steps listed below:

a. Open the front cover.

b. Lift the drum unit slightly and pull it out. Place the drum unit on
adrop cloth or large piece of disposable paper to avoid spilling and
scattering the toner.

c. Remove the toner cartridge from the drum by holding down the lock
lever (blue tab) on the left side of the drum unit and lift the toner
out.
*Handle the toner cartridge carefully. If toner scatters on your hands
or clothes, immediately wash it off with cold water.

d. Gently rock the toner cartridge from side to side five or six times
to distribute the toner evenly inside the cartridge.

e. Place the toner cartridge into the drum (be sure it clicks into
place).

f. Clean the primary corona wire inside the drum unit by gently sliding
the blue tab on the top of the cartridge from right to left several
times. Return the blue tab to the home position before reinstalling the
drum unit assembly.

g. Reseat the drum unit into the machine.

h. Close the front cover.

2. If the message "Toner Life End" continues to appear on the display,
contact Brother Customer Service at 1-877-Brother (276-8437) Monday
through Friday, 9:00am - 7:00pm EST, excluding holidays.

http://www.brother-usa.com/FAQs/Solution.aspx?FAQID=100000004309&Sympt=I+just+replaced+the+toner+cartridge+and+the+LCD+continues+to+display+themessage+Toner+Life+End.+What+can+I+do%3f&Model=99&ProductGroup=5&Keyword=toner&ProductID=MFC7420