getting faint, streaky prints or lines down the page, already swapped the toner and it didn't help.

Diagnosis

The persistence of streaks or faint printing after replacing the toner cartridge indicates that the issue lies within the imaging system, specifically the Drum Unit or the Transfer Roller. In the Canon imageClass LBP236dw, the toner cartridge only provides the powder; the Drum Unit is the component that electrically charges the page and transfers that powder onto the paper. When the organic photoconductor (OPC) coating on the drum wears down or becomes scarred, it creates "blind spots" where toner cannot adhere, resulting in vertical white streaks. Conversely, if you are seeing dark streaks or repeating spots, it is likely a physical defect—such as a speck of adhesive from a label or a piece of dust—stuck to the drum's surface. Because the drum rotates for every single page, a single microscopic piece of debris will leave a mark at the exact same interval down the page. You can confirm this by checking the "Drum Life" percentage in the printer's Status Monitor on your PC; if it is below 20%, the drum is chemically exhausted and can no longer hold a consistent charge.

How to Fix It

To resolve this, you must address the Drum Unit (Canon Cartridge 053 series compatible drum). Follow these precise steps:

1. Power down the printer and open the front cover fully to expose the internal carriage.
2. Grasp the handle of the toner cartridge and pull it straight out of the machine. Set it aside on a clean sheet of paper to avoid toner leakage on your furniture.
3. Locate the Drum Unit, which is the larger assembly that the toner cartridge was seated into. Grasp the green release lever/handle on the drum unit and pull the entire assembly out of the printer chassis.
4. Inspect the green/blue cylindrical roller on the drum. If you see a physical ring of toner or a scratch that matches the pattern on your printed page, the unit is physically damaged.
5. If the drum is merely dirty, use a dry, lint-free microfiber cloth to gently wipe the surface. Do not use alcohol or solvents, as these will strip the photosensitive coating.
6. If the streaks persist, replace the Drum Unit with a new genuine Canon part. Slide the new unit into the guide rails until it clicks firmly into place.
7. Reinsert the toner cartridge into the drum unit, ensuring it snaps securely. Close the front cover and run a "Print Test Page" from the System Management menu to verify the image density.

If That Didn't Work

• Clean the Corona Wire: Locate the small sliding tab (usually green) on the drum unit. Slide it back and forth 3-4 times across the full width of the printer. This cleans the charging wire that prevents "ghosting" or light vertical bands from appearing.
• Check the Transfer Roller: Look inside the printer cavity beneath where the drum sits. There is a black foam roller (the Transfer Roller). If this is coated in leaked toner or has a physical indentation, it will cause faint horizontal streaks. Gently clean it with a vacuum or a very soft brush; never touch this roller with your bare fingers as skin oils cause print voids.
• Adjust Print Density: Access the printer's onboard menu: Settings > Preferences > Timer/Energy > Print Quality. Increase the "Toner Density" setting by 1 or 2 notches. This forces the laser to dwell longer on the drum, which can mask minor wear in the OPC layer.
• Verify Paper Weight Settings: If you are using heavy cardstock or labels, the printer may be under-fusing. Go to the Paper Settings menu and ensure the "Paper Type" is set to "Heavy" or "Label" rather than "Plain." This slows the paper speed through the fuser, ensuring the toner is melted completely into the fibers.

Heads Up

• Light Sensitivity: Never leave the Drum Unit exposed to bright indoor light or direct sunlight for more than a few minutes. Prolonged exposure "burns" the drum, which will result in permanent white streaks that cannot be cleaned.
• Avoid Abrasives: Never use a paper towel or a scrub brush on the drum surface. The OPC layer is incredibly thin; a single scratch from a coarse paper towel will create a permanent line on every page you print.
• Toner Compatibility: If using third-party "compatible" toner, be aware that low-quality powder can be too abrasive, wearing out the Drum Unit significantly faster than genuine Canon supplies.
• Firmware Updates: Ensure your LBP236dw is running the latest firmware. Canon frequently releases updates that optimize the laser intensity and drum charging voltage to extend the life of consumables.