Black Dots, Streaks or Grey Background: Diagnose It in Three Steps

Troubleshooting · 2026-10-24

Print a page, look at it against the light, then rub one of the marks with your fingertip. That single action separates "the toner is finished" from "the drum is damaged" from "the paper is damp" — and roughly half the cartridges replaced for print defects did not need replacing.

Step one: is the position fixed, or does it move?

Print three pages. Compare where the marks appear.

Same place every time → the cause is a rotating part inside the machine. The mark lands where that part touches the paper.

Different every time → usually the paper: damp stock, paper dust, or static. Try a fresh ream from a sealed pack before spending anything.

Step two: rub it

This is the fastest single test and most people skip it.

Result	What it means	What to do
Smudges off; black powder on your finger	Toner was never fused onto the page — a fuser or paper problem	Try new paper. If it persists, the fuser needs service — not a new cartridge
Will not rub off; paper feels dented	The drum or a roller has scratched the paper	Replace the cartridge
Comes off as a grey film across the page	Damp paper or a worn drum	New paper first; if unchanged, cartridge

If the toner rubs off, buying a cartridge is the wrong purchase. The fuser is not melting the toner, and a new cartridge will produce exactly the same result.

Step three: measure the repeat distance

The most precise check, and almost nobody does it.

Measure from one defect to the next. If the spacing repeats at a fixed distance, the cause is a rotating cylindrical part — because a roller deposits one mark per revolution, and the repeat distance equals that roller's circumference.

• Short repeat (a few centimetres) — the developing roller or the drum
• Long repeat (close to 10 cm) — the fuser roller
• Vertical line running the full page length — a scratch along the drum, which is direction-of-travel damage rather than a circumference mark

Once you know which part, you know what to buy. That is the whole point of the measurement.

Common defects at a glance

Symptom	Most likely cause	Action
Black dots, rub off	Fusing failure / damp paper	New paper; service the fuser
Black dots, will not rub off, paper dented	Drum or roller surface damage	Replace cartridge
Vertical fine lines, fixed position	Drum scratch or toner clumping	Inspect drum; replace if scratched
Grey background across the page	Low toner, worn drum, damp paper	Paper first, then cartridge
One side darker than the other	Toner exhausted on one side of the hopper, or printer not level	Rock the cartridge gently; if unchanged, replace
Vertical white line	Dirty laser window or mirror	Clean — no parts needed

When replacement is genuinely the answer

Three signals, any one of which means stop trying to save it:

1. Print is visibly light and you have already refilled once
2. A fixed black or white line that will not rub off and does not move between pages
3. Heavy grey background that new paper does not fix

Everything else is worth diagnosing first. A cartridge costs five to eight times a refill, and a fuser service is cheaper than either — but only if you identify the fault correctly.

Common questions