Why is my printer leaving a black line?
When your printer leaves black lines, the lines indicate that there are excess toner powders on the rollers or transfer belt within the printer. As the paper is moved along by the rollers and transfer belt, any excess powder left on them can result in lines being left on the paper.
How do I clear black vertical lines or streaks on printed documents?
This issue is usually caused by foreign material inside the machine (paper dust, glue from labels or envelopes, paper clips, staples, etc.) sticking to or damaging the surface of the drum. This is typically resolved by cleaning and/or replacing the drum unit.