Printer Making Bumping Noises and Leaving Black Spots/Indent Marks: How to Find What the Printhead Carriage Is Hitting

Question: I'm in New Zealand and hoping you can give me some advice. My prints have black spots and "grooving" on the back, but the nozzle check is perfect (all nozzles print). While printing, I hear bumping sounds, and every bump creates a black mark on the page-about 7 bumps across an A4 pass, and this repeats about 7 times down the page. Lined up with those bumps are indents on the back of the paper (about 6 mm long and 1 mm wide). The bumping happens on every printhead pass, even when the printer is just moving into position and not printing. It also seems like the printhead isn't maintaining a platen gap and is scraping the plastic ridges underneath its travel. What could be causing this?

Answer: 

Based on your description, this sounds mechanical rather than electronic, and that's good news-because mechanical contact issues are often solvable once you identify the exact interference point.

You already provided the strongest diagnostic clue: the nozzle check is perfect, yet you're getting repeating marks plus audible bumps, and the marks repeat at consistent intervals across and down the page. That pattern is classic for the printhead carriage (or something attached to it) hitting a fixed part of the printer at regular spacing, or for paper being driven over a contaminated roller/spur that re-stamps the page at consistent distances.

Why the marks repeat in a predictable pattern

When defects occur:

• At even intervals left-to-right (during each pass), and

• At even intervals top-to-bottom (down the page),

it usually means one of these is happening:

1) The carriage is physically striking something along its travel

Each time the carriage hits the same obstruction, you hear a "bump." That vibration can:

• cause the head to momentarily dip and touch paper (leaving black marks),

• scrape a plastic rib/ridge (leaving contact noise),

• or smear ink if the underside of the head/carriage picks up residue and then stamps it repeatedly.

2) A roller/spur/star wheel is marking the page repeatedly

Some printers have paper drive rollers, pinch rollers, and small star wheels/spur rollers that ride on the paper. If one is dirty with ink/grease or damaged, it can create:

• repeating black spots,

• repeating "grooves" or dents on the back,

• and the repeat distance will match the circumference/spacing of the roller system.

However, your note that bumping happens even when not printing (during movement/initialization) leans more toward carriage contact than paper-roller-only issues.

What your symptoms strongly suggest

You said: "The printhead is not maintaining any platen-gap, fouling the plastic ridges just underneath its travel."

That points to a platen gap / carriage height / alignment issue, or something that effectively reduces the gap, such as:

• a mis-seated printhead carriage assembly,

• a loose or skewed carriage guide/rail,

• a displaced encoder strip or cable bundle rubbing underneath,

• a worn/damaged carriage bushing,

• or the paper not being held down properly (paper buckling upward into the head path).

And your proposed diagnosis is very plausible: a roller assembly in the rear (often a darker/black roller) may not be holding the paper flat, allowing the page to lift and get struck by the carriage/head at repeated points. Alternatively, the carriage may be striking the roller or a guide component at a consistent interval.

The most effective way to fix this: identify the exact contact point first

Your proposed approach is the right one: don't adjust randomly-find what is physically making contact.

Step 1) Find out whether the mark is from the front or from the back

• If the black mark is on the printed side, it may be ink being smeared by the head underside, wiper contamination, or carriage impact causing head-to-paper touch.

• If the groove/indent is on the back side, it's often a roller/spur/platen impression.

Because you have both black marks and back-side indents aligned with the bumps, the most likely scenario is:

• something bumps → paper/head contact occurs → paper gets dented and ink gets stamped/smeared.

Step 2) Remove the right-side panel and observe during printing (as you suggested)

If your printer design allows it safely, taking the right-side panel off can let you visually confirm:

• where the carriage is during the bump,

• whether a cable harness is snagging,

• whether the carriage dips,

• whether paper is lifting into the head path,

• or whether a roller is wobbling.

A practical method:

• Use a flashlight.

• Run a short print or even a maintenance movement (anything that makes the carriage sweep).

• Watch the underside path where the carriage passes over plastic ridges or roller structures.

Goal: identify which exact part touches at the bump.

Step 3) Check the "paper hold-down" parts: rollers and star wheels

Your suspect is a strong one: the rear black roller (or related hold-down rollers) that help keep paper flat.

What to look for:

• roller not seated properly,

• roller shaft popped out of a cradle,

• uneven pressure from left to right,

• damaged roller surface,

• paper skewing or "tenting" upward.

Also check star wheels/spurs:

• If one is bent or has ink buildup, it can create repeated tracks and dents.

Step 4) Inspect for carriage rubbing points

Common mechanical "hit" sources:

• a cable bundle hanging low (FFC ribbon or harness not clipped correctly),

• a displaced encoder strip path or guide,

• a broken plastic tab protruding into the travel area,

• debris lodged on the platen ribs,

• a service station component not resetting fully (wiper/cap assembly not retracting).

Because you hear bumps even when not printing, a fixed protrusion or misaligned component along the carriage path is especially likely.

Adjusting the platen gap / carriage height (only after you find the collision)

You mentioned the printhead is not maintaining a platen gap. Some printers have a platen gap lever, paper thickness setting, or mechanical adjustment that changes the carriage-to-paper distance. If yours does, increasing the gap can reduce rubbing-but it's not a true fix if something is broken or mis-seated.

A correct repair sequence is:

1. Identify the part being struck,

2. Correct the alignment/seating/angle of that part,

3. Then confirm the platen gap is appropriate and paper is held flat.

If you adjust the gap without addressing the collision, the problem often returns and can worsen (more smearing, head damage, or paper feed damage).

Why this is "likely easy" (as you noted)

Because:

• Your nozzle check is perfect (ink system and firing are working),

• There are no electronic error codes mentioned,

• The defect is rhythmic and audible,

• And you can physically correlate each bump with a mark,

This points to a repeatable mechanical interference, not a random electronic failure. Once the interfering part is found, the fix is usually a reseat, realignment, replacement of a worn roller/spur, or correcting a carriage-path obstruction.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. So, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We offer an in-person evaluation and repair service via our local diagnostic facility: printer repair service (https://bchtechnologies.com/printer-repair-service). Given the high demand, we operate on a first-come, first-served basis, so it might take a few weeks before we can get your printer in for drop-off. Our services are structured to repair either a whole printer or specific parts, with clear instructions on how to proceed. However, we acknowledge that our rates aren't the most economical. Thus, we highly recommend that you resort to self-help via online research. You can start by checking out YouTube or visiting our YouTube channel's homepage: BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). Look for specific videos using the search icon next to "About" on the right-hand side of the menu bar. I receive dozens of queries every day asking about videos for specific topics. Having created videos over the past nine years, it's challenging to remember every single one. Therefore, using YouTube's search function would be most efficient. Plus, YouTube might suggest relevant videos from other channels that could assist you.

Thank you again for reaching out from New Zealand, and I appreciate the detailed symptom description-it actually helps a lot with mechanical issues like this. I hope the process above helps you quickly pinpoint what the printhead carriage is striking (often a roller/hold-down assembly or a protruding obstruction) so you can correct it and stop the bumps, marks, and back-side grooves.