Hello and thanks for your question. I look forward to assisting you today with the best answer possible.
Sorry to hear about your issue.
The most likely cause to this type of problem is the area where the black cartridge is dirty with left over ink and it has blocked the cartridge sensor.
Could you please remove the new black cartridge and inspect area where the black cartridge sits and tell me if its clean or smeared with ink?
Did you try cleaning the drum unit ?
Did you clean the corona wire ?
As of first step we will clean the corona wire. I'll give you a guide which will help you clean the Corona wire.
Please click this link to access the guide: http://support.brother.com/g/b/faqend.aspx?c=us&lang=en&prod=mfc9125cn_us_as&faqid=faq00000208_026
Tell me if it makes any difference to your problem.
I am sorry to give you a bad news. I just want to be honest with you.The most likely and common cause to this type of problem is either a bad transfer belt as well or a bad image drum.But before going for replacement we will have to try cleaning the printer. For cleaning you need to have toner cloth, toner vacuum, a paint brush.Please follow the steps below:1. Open the printer and remove the toner cartridge.2. Use a toner cloth and wipe the toner cartridge.3. Then using your toner vacuum remove spilled toner from within the printer’s internal compartment. Make sure the vacuum’s nozzle is not actually touching any of the printer's internal surfaces.4. Then using a paintbrush, remove toner from any crevices. Use gentle motions and vacuum as necessary.5. Then dip a cotton swab into isopropyl alcohol and gently run it along the length of the Corona wire. Also be sure to clean the underside of the wires. Never apply pressure.6. After that replace everything back.If the cleaning doesn't works then it verifies that the transfer belt and image drum needs to be replaced.If you don't have the toner vacuum, toner cloth then it will be very expensive for you to perform this cleaning operation because a new toner vacuum will cost you around 200-300$.I would suggest you to take the help of a local printer repair shop to do the cleaning and replace the necessary part.I can give you the contact of a local printer repair shop near your area, if you tell me your city name.Is there anything else I can help you with ?