Lines on a laser printout are rarely random. Their direction, color, and spacing point to the part that’s causing them. A 10-minute check usually tells you whether you need to clean something, replace the toner cartridge, or replace the drum, so you don’t buy parts you don’t need.
Quick answer
- Vertical black lines usually come from a dirty corona wire, a scratched or dirty drum, or a toner cartridge that’s leaking.
- Vertical white lines usually mean the toner is low or packed to one side, the laser window is dirty, or debris is stuck on the developer blade inside the cartridge.
- Horizontal lines or marks that repeat come from a roller. Measure the gap between marks to find out which one.
- Lines only on copies, not prints? Clean the scanner glass. The printer is fine.
Step 1: Match your lines to a pattern
Print a page with plenty of solid black or gray on it. A printer test page, a configuration report, or a full-page photo works well. Then hold it in the direction it came out of the printer. “Vertical” in this guide means the lines run the same direction the paper traveled.
Thin vertical black lineSame spot on every page. Usually the corona wire, the drum, or leaking toner. Vertical white lineA gap where toner is missing. Usually low toner, a dirty laser window, or debris on the developer blade. Faded stripe on one sideLight on one side, normal on the other. Usually toner that’s low or packed unevenly. Horizontal lines that repeatEvenly spaced across the page. A roller has a flaw. Measure the gap. Repeating dots or marksSame spacing every time. Usually a nick or stuck toner on the drum. Gray streaks or hazeA dirty gray tint over the page. Usually a worn drum or charge roller.
Why laser printers print lines (the 60-second version)
A laser printer builds every page in six quick stages. Toner only lands where it should if each surface along the way is clean, smooth, and evenly charged.
- ChargeA charge roller or corona wire gives the drum an even electrical charge.
- ExposeThe laser “draws” your page on the drum by changing the charge where text and images go.
- DevelopThe developer roller and its blade spread a thin, even layer of toner onto the drawn areas.
- TransferThe transfer roller pulls the toner off the drum and onto the paper.
- FuseThe fuser melts the toner into the paper with heat and pressure.
- CleanA wiper blade scrapes leftover toner off the drum before the next turn.
- Charge roller or corona wire. Dirt here causes black lines or gray haze.
- Laser window. Dust here causes white lines or faded areas.
- Developer roller and blade. Debris here causes thin white lines.
- Drum. Scratches cause black lines. Nicks cause repeating marks.
- Transfer roller. Dirt causes faint areas or toner on the back of the page.
- Fuser. Wear causes smears, ghosting, and repeating marks.
Here’s the key idea. Paper moves past each part in one direction. A flaw at one fixed point, like a scratch on a blade or a speck on the laser window, draws a line straight down the page. A flaw on the surface of a roller touches the page once per turn, so it prints marks or lines that repeat at an even spacing.
Is the drum part of your toner cartridge? Many HP and Canon laser cartridges have the drum built in, so a new toner cartridge also gives you a new drum, developer roller, and wiper blade. Most Brother laser printers use a separate drum unit that lasts through several toner cartridges. Lexmark, Dell, Xerox, and Samsung vary by model. Check your printer’s manual or the cartridge listing before you buy anything, because it changes which part you replace.
Vertical black lines: causes and fixes
Work through these in order. The first steps are free and fix the problem more often than you’d expect.
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Clean the corona wire Free
If your printer uses a separate drum unit, as most Brother models do, take the drum and toner assembly out and find the small tab (often green) on top of the drum. Slide it gently from one end to the other several times. Then return it all the way to its home position until it clicks. If you leave it in the middle, it will print a new vertical line of its own.
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Look for loose toner Free
With the cartridge out, check the cartridge and the inside of the printer for spilled toner. Wipe it away with a dry, lint-free cloth. Don’t use a household vacuum. Toner is fine enough to pass through ordinary filters, and the static can be a fire risk. Use a toner-rated vacuum or a cloth.
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Inspect the drum Free
Look at the drum’s surface (usually green or blue) without touching it. A scratch, a spot of stuck toner, or a bit of label glue that lines up with your black line confirms the drum as the cause. On separate drum units you can usually turn the drum by its gear to see the whole surface. Keep the drum out of bright light, and don’t leave it exposed for more than a few minutes.
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Try a new toner cartridge $
If the line moves, changes, or disappears, the old cartridge was leaking or (on all-in-one cartridges) its built-in drum was damaged.
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Replace the drum unit $$
If you have a separate drum and the line stays with a new toner cartridge, the drum is the next suspect, especially if it’s near the end of its rated life. Most printers show drum life on the control panel or the printer’s status report.
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Check the fuser $$$
If a new toner cartridge and drum didn’t help, the fuser may be scratched. Fuser lines often look a little smeared or shiny instead of crisp. A fuser or maintenance kit fixes it, but it’s usually the most expensive part, so rule out everything else first.
Lines only on copies or scans? If printed documents look clean but photocopies have a line, the problem is on the scanner side, not the print side. Clean the flatbed glass and the thin glass strip on the left side under the document feeder with a soft cloth and a little glass cleaner. Never spray the cleaner directly on the glass. A single speck on that strip draws a line down every copy.
Vertical white lines and faded streaks
White lines are gaps where toner never reached the paper. They’re usually a supply or blockage problem, not a damaged part.
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Redistribute the toner Free
Take the toner cartridge out and gently rock it side to side five or six times, keeping it level. Toner packs to one side as it runs low, which leaves faded stripes. If this helps, the cartridge is close to empty, so have a replacement ready.
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Clean the laser window Free
Some printers have a laser scanner window you can reach behind the cartridge or through a small slot. Your manual will show where it is and what to clean it with. Wipe it gently with a dry, lint-free cloth or the cleaning tool the manual names. Dust here causes clean-edged white lines.
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Check the paper Free
Paper that has soaked up humidity doesn’t take toner evenly. Load paper from a freshly opened ream and see if the streaks go away.
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Replace the toner cartridge $
A sharp, thin white line that stays in the same spot after the steps above is usually a fiber or clump stuck on the developer blade inside the cartridge. You can’t reach it, so a new cartridge is the fix.
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Check the transfer roller $$
The black sponge roller under the cartridge moves toner to the paper. If it’s dented, worn, or dirty, you’ll see faint or patchy areas. Don’t touch it with your fingers, because skin oil causes the same problem. Replacing it is often a job for a technician.
Horizontal lines and repeating marks: measure the gap
Marks that repeat at the same spacing are the easiest problem to diagnose. Each roller has one size, so it touches the page at one fixed interval. Measure from the top of one mark to the top of the next. That distance is the roller’s circumference.
Every printer model has its own numbers, and different parts can share a distance. For example, HP’s print quality guide for its LaserJet Enterprise M880 lists 41 mm for the charge roller, 47 mm for the developer roller, 75 mm for the fuser sleeve, and 94 mm for the drum or the fuser pressure roller. To tell those last two apart on a color printer, check the colors. A mark in every color points to the fuser, and a mark in one or two colors points to that color’s drum.
For your exact model, search for “[your printer model] repetitive defects” or look in the print quality section of your manual. Many manufacturers publish a table or a printable ruler.
Horizontal lines that don’t repeat evenly are a different problem. A single dark or light band across the page can come from the printer being bumped mid-print, a worn drive gear, or a printer that isn’t sitting level. Print a few more pages. If the band moves around, check that the printer is on a flat, solid surface and that nothing is pressing on it.
Gray streaks and background haze
A light gray tint over the whole page, sometimes with darker vertical streaks, means toner is landing where the drum should have kept it away. The usual causes, from most to least likely:
- A worn drum. Drums lose their ability to hold a clean charge near the end of their life. If your drum’s page count is near its rating, replace it.
- A dirty charge roller or corona wire. Clean the corona wire as described above. Charge rollers inside all-in-one cartridges are replaced with the cartridge.
- Print density set too high. Check the toner density or darkness setting in the printer menu and set it back to the default.
- Humidity or damp paper. Haze that comes and goes with the weather points to moisture. Store paper sealed and off the floor.
If pages come out smeared or the toner rubs off when you touch it, that’s a fusing problem rather than a line problem. See our guide to fixing laser printer smudges and dirty pages.
Cheat sheet: symptom, cause, fix
| What you see | Most likely cause | Try first (free) | Replace if that fails |
|---|---|---|---|
| Thin vertical black line | Dirty corona wire, scratched drum | Slide the corona wire cleaner, inspect the drum | Drum, or toner cartridge if the drum is built in |
| Wide black streak at the edge | Toner leaking from the cartridge | Remove and wipe out loose toner | Toner cartridge |
| Sharp vertical white line | Debris on the developer blade, dirty laser window | Clean the laser window | Toner cartridge |
| Faded stripe on one side | Low or unevenly spread toner | Rock the cartridge side to side | Toner cartridge |
| Marks repeating at an even gap | Flaw on a roller (drum, charge, developer, fuser) | Measure the gap and match it to your model’s chart | The matching part |
| Gray haze over the page | Worn drum, density set too high | Reset density, clean the corona wire | Drum |
| Lines on copies only | Dirty scanner glass | Clean the glass and the feeder strip | Nothing, it’s a cleaning job |
| Smeared line after new toner and drum | Scratched fuser | Run the printer’s cleaning page, if it has one | Fuser or maintenance kit |
Step-by-step decision path
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Does the line show up on printed documents, or only on copies?
- Copies only
- Clean the scanner glass and the document feeder strip. You’re done.
- Prints too
- Go to question 2.
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Does it run the same direction the paper traveled (vertical)?
- Yes
- Go to question 3.
- No, it runs across
- Go to question 4.
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Is the line black or white?
- Black
- Clean the corona wire, wipe out loose toner, and inspect the drum. Still there? Try a new toner cartridge, then the drum.
- White
- Rock the toner cartridge, clean the laser window, and try fresh paper. Still there? Replace the toner cartridge.
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Do the marks repeat at the same spacing?
- Yes
- Measure the gap and match it to your model’s repetitive defect chart. About 75 mm or 94 mm usually means the drum.
- No
- Make sure the printer is level and isn’t being bumped, then print again.
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Still there after a new toner cartridge and drum?
- Yes
- The fuser, transfer roller, or the printer itself needs attention. Check the fuser’s page count, or call a technician.
Lines right after installing a new cartridge?
Any toner cartridge, name brand or aftermarket, can be damaged in shipping or leak if it was dropped. If lines start right after a cartridge swap:
- Make sure you pulled out all of the packing material, including the sealing strip and any plastic clips on the drum or roller.
- Rock the new cartridge gently to spread the toner, then reinstall it firmly.
- Print five to ten pages. A few lines that fade away were loose toner from shipping.
- Put the old cartridge back for one test page. If the lines disappear, the new cartridge is the problem.
If a cartridge you bought from Swift Ink causes lines, contact our support team and we’ll help you sort it out. You can also review our returns and exchanges policy.
How to keep lines from coming back
- Slide the corona wire cleaner every time you change the toner, if your drum has one.
- Replace the drum when the printer says it’s at the end of its life. Don’t wait for the lines.
- Use paper and labels made for laser printers. Inkjet labels and glossy inkjet paper can leave adhesive or coating on the drum and fuser.
- Keep paper sealed and dry, and keep the printer on a level surface away from heaters and open windows.
- Don’t touch the drum or the transfer roller, and don’t leave a drum sitting in bright light.
Frequently asked questions
Why is my laser printer printing lines after I changed the toner?
The most common reasons are leftover packing material, toner that settled in shipping, or a cartridge that was dropped. Remove all packing pieces, rock the cartridge, and print several pages. If the lines stay, put the old cartridge back for one test page to confirm the new one is the cause.
Should I replace the toner or the drum first?
If your drum is built into the toner cartridge, replace the cartridge, since it replaces both. If you have a separate drum, check its remaining life on the printer’s status page. Replace the toner first if the drum still has plenty of life. Replace the drum first if it’s near the end.
Can I clean a drum unit?
You can clean the corona wire and gently remove a spot of stuck toner with a dry cotton swab, if your manual allows it. Scratches can’t be fixed. A scratched drum has to be replaced.
Why are the lines only on one side of the page?
A faded or streaky band on one side usually means low or unevenly spread toner. A dark streak at one edge usually means toner is leaking from the end seal of the cartridge or drum. Rock the cartridge first. If you see loose toner at the edge, replace the cartridge.
Can the fuser cause vertical lines?
Yes. A scratched or worn fuser can print lines that look smeared or slightly glossy, and it often causes repeating marks too. Rule out the toner cartridge and drum first, because they’re cheaper and more likely to be the cause.