MFC-9970 black line down page - Brother MFC-9840CDW Laser Printer

SOURCE: mfc-7420 ,when sending faxes puts

See if there is a part of the roller that makes a crease on teh paper The black line means that sensor on your end sees a mark on the paper and interprets that as a message or a charachter hence turns it into a line

SOURCE: Black stripe down middle of page when copying

open the top cover on the left hand side glass plateform with a narrow piece glass clean it with alcohol.

SOURCE: Black line down middle of page

Clean the inside of the printer with a soft rag, be gentle and get as much toner up as you can, also your toner carttridge may be empty or the crum may be bad, start with a fresh toner carttridge and clean the printer out where the cartridge sits.

SOURCE: mfc-7420 Black Line horizontal across paper in 3 places

try moving the small blue slider on top of the drum cartridge side to side 10 times.

SOURCE: black line down page when coping from copy feed

The small glass surface at the top of the scanner bed had some gunk on it. I scrapped it off and the line went away! Yay!