Why Does My Canon MG3520 Print Wavy or Smudged Black Lines While Color Prints Straight?

Question:
I'm having a problem with my Canon MG3520 printer. When I print in black, the lines come out wavy or smudged, but when I print in color, everything looks straight and fine. I've already tried swapping different black cartridges, but the problem stays the same. What could be causing this issue?
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Answer:

We at BCH Technologies (https://bchtechnologies.com) truly appreciate your engagement and support, particularly for our YouTube channel (https://youtube.com/@bchtechnologies). Your feedback helps us continue refining our repair methods and sharing our technical expertise with the printing community.

Now, regarding your Canon MG3520 producing wavy or smudged black lines while color prints appear straight - this issue is quite common, and it's not always caused by a clogged printhead. Since you've already tested multiple black cartridges and the problem remains, that indicates the issue lies deeper in the mechanical or alignment system, not the cartridge itself.

Here are the most likely causes and how to address them:

1. Printhead Alignment Issue

The most frequent cause of wavy or crooked black lines is a misaligned printhead. Even a slight deviation in the printhead's position can cause the nozzles to fire ink in slightly off directions, leading to uneven or fuzzy text.

Fix:

• Run a Printhead Alignment from your printer's maintenance menu.

  • On the Canon MG3520, go to Settings → Maintenance → Print Head Alignment.

  • Follow the on-screen instructions and print the alignment sheet.

  • If alignment fails or doesn't help, you may need to manually clean the encoder strip (see below).

2. Dirty or Smudged Encoder Strip

The encoder strip is a thin, clear plastic strip that runs behind the printhead carriage. It tells the printer exactly where the printhead is as it moves. If this strip gets dirty with ink mist or fingerprints, the printer can misread positioning data, leading to jittery or wavy print lines.

Fix:

• Turn off and unplug your printer.

• Open the top cover and locate the clear plastic strip running behind the carriage.

• Gently clean it with a lint-free cloth dampened with distilled water or isopropyl alcohol (90% or higher).

• Move the carriage left and right carefully to reach both ends of the strip.

• Allow it to dry completely before powering the printer back on.

3. Paper Feed or Roller Slippage

If the paper is not fed evenly or slips slightly during printing, it can distort only the black lines (since text or black-filled patterns use higher ink density).

Fix:

• Check the paper feed rollers for buildup of dust, paper fibers, or dried ink.

• Use a soft cloth dampened with roller cleaning fluid or water to gently clean them.

• Allow the rollers to dry fully before use.

• Always use high-quality, flat paper - wrinkled or damp sheets can make the issue worse.

4. Printhead Mechanical Wear or Mounting Problem

If you've refilled cartridges multiple times or used the printer for a long period, the printhead bracket or rail may have slight looseness or debris buildup. This can cause vibration or slight tilt during printing, leading to the "wavy" black lines you see.

Fix:

• Inspect the carriage rail and ensure it's free of ink buildup or dried lubricant.

• Apply a tiny amount of silicone-based lubricant to the rail if it feels sticky or uneven.

• If the printhead doesn't sit snugly in its slot, remove and reinsert it carefully until it clicks into place.

5. Print Density Difference Between Black and Color

Black nozzles typically use pigment ink, while color cartridges use dye ink. Pigment ink is thicker and more sensitive to slight misalignment or airflow in the nozzle chamber. If the black ink channel has air bubbles or partial clogging (even if not fully blocked), it can cause uneven droplet ejection.

Fix:

• Perform a deep cleaning cycle (maintenance → deep cleaning → black).

• Afterward, print a nozzle check pattern to verify that the black lines are even and complete.

• If one section looks faded or jagged, repeat the cleaning cycle once or twice.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. Therefore, we're not able to provide remote troubleshooting or detailed repair support. However, we do offer in-person printer evaluation and repair services through our local diagnostic facility (https://bchtechnologies.com/printer-repair-service). Given the high demand, our repairs operate on a first-come, first-served basis, and it might take a few weeks before we can work on your unit. Our services include complete printer repair or targeted part replacement, with clear guidance for each case.

If you prefer to resolve the issue yourself, we encourage you to visit our YouTube channel (https://youtube.com/@bchtechnologies) and use the search icon near the "About" section to find specific videos. Over the past nine years, we've created hundreds of detailed tutorials, and YouTube's built-in search makes it easier to locate the exact one you need.

Thank you again for reaching out and for supporting BCH Technologies. We appreciate your patience and your dedication to keeping your Canon printer performing at its best!