prints are coming out with faint vertical lines or streaks down the page, new toner cartridge

Diagnosis

Faint vertical lines or streaks on a Brother DCP-L2640DW, especially after installing a fresh TN830 or TN830XL toner cartridge, typically indicate a contamination issue on the Drum Unit (DR830) rather than a failure of the toner itself. These streaks occur when a microscopic piece of debris, a speck of dust, or a clump of dried toner adheres to the corona wire or the surface of the organic photoconductor (OPC) drum. As the drum rotates, this debris creates a continuous line of static charge or physical displacement, resulting in a vertical streak on every single page. To confirm the source, you must determine if the streak is consistent in position. If the line is perfectly straight and appears in the exact same spot on every page, the issue is almost certainly a dirty corona wire or a scratch on the drum. If the lines are irregular or appear as "smudges" that repeat at specific intervals (roughly every 3-4 inches), the problem is likely a physical defect or a piece of debris stuck to the drum roller. If the streaks are faint and greyish, it is often a failure of the internal cleaning blade within the drum assembly to scrape away excess toner.

How to Fix It

To resolve vertical streaking, you must perform a deep manual cleaning of the drum and corona wire. Follow these precise steps:

1. Power off the printer and open the front cover.
2. Grasp the handles of the toner/drum assembly and pull it straight out of the machine.
3. Press the green lock lever on the drum unit to release the toner cartridge. Lift the toner cartridge (TN830) out and set it aside on a clean sheet of paper to avoid leaking toner on your furniture.
4. Locate the green sliding tab on the top of the drum unit (DR830). This is the corona wire cleaner.
5. Slide the green tab from left to right and back again several times. Ensure you slide it across the entire width of the unit.
6. CRITICAL: Slide the green tab back to its original "Home" position (indicated by a small arrow). If the tab is left in the middle or at the end, the printer will produce a massive black vertical stripe down the center of every page.
7. Inspect the surface of the black roller (the drum). If you see a spot of toner or a piece of dust, gently wipe it away using a clean, dry cotton swab dampened with a tiny amount of isopropyl alcohol. Do not use a paper towel or a sharp object, as scratching the drum will permanently ruin the unit.
8. Reinsert the toner cartridge into the drum unit until it clicks, slide the assembly back into the printer, and close the front cover.

If That Didn't Work

• Replace the Drum Unit (DR830): If the streaks persist after cleaning the corona wire, the drum surface is likely physically scratched or the internal wiper blade has worn out. The toner cartridge and drum unit are separate components; replacing the toner does not replace the drum. Install a new DR830 drum unit and reset the drum counter via the Settings menu.
• Inspect the Fuser Assembly: If the streaks appear as "smears" or the toner is not fully bonded to the paper (it rubs off with your finger), the fuser unit is failing. Check the rear of the printer for any torn scraps of paper or melted plastic that may be stuck to the heat rollers.
• Check Paper Settings: If you are using heavy cardstock or labels but the printer is set to "Plain Paper," the fuser may not reach a high enough temperature to bond the toner, causing vertical "ghosting" or streaks. Go to Settings > Paper Tray > Paper Type and select "Thick" or "Recycled" to increase the heat.
• Perform a Hard Reset: Occasionally, a static build-up in the transfer roller can cause faint lines. Unplug the power cord from the wall for 60 seconds, hold the power button down for 15 seconds while unplugged to drain the capacitors, then plug it back in.

Heads Up

• Never touch the black surface of the drum unit with your bare fingers; skin oils can create permanent "voids" or spots in your prints.
• Always ensure the green corona wire slider is returned to the home position, or you will experience total page saturation.
• Avoid using "compatible" or "generic" toner cartridges that lack a proper seal, as leaking toner often settles on the drum and causes the very streaks you are trying to fix.
• Keep the printer in a climate-controlled environment; extreme humidity can cause the toner to clump, leading to irregular vertical banding.