how do you clean the inside of a canon pixma mg3620? it's smudging the backs of my pages

Diagnosis

The smudging on the back of your pages is caused by an accumulation of waste ink and paper dust on the bottom plate (the internal platen) of the Canon PIXMA MG3620. This occurs because the printer uses a "U-turn" paper path; as the page is flipped for double-sided printing or simply passed through the rollers, it presses against the bottom surface of the chassis. Over time, ink mist from the print head or leaked ink from the PG-24/CL-24 cartridges settles on this plate.

You can confirm this is the issue if the smudges appear as consistent streaks or "ghosting" patterns on the side of the page that was facing down during the second pass. If the smudging is random or splotchy, it may be a roller slip, but consistent linear marks almost always indicate a dirty bottom plate that needs a physical "wipe" using a sacrificial sheet of paper.

How to Fix It

To perform a Bottom Plate Cleaning, you must use a specific folding technique that allows the paper to act as a scrub brush, reaching the furthest corners of the internal chassis without jamming the machine. Follow these precise steps:

1. Power on the printer and ensure there are no error codes (like E03 or P02) on the small LCD screen. Remove all existing paper from the rear tray to avoid double-feeding.
2. Take one single sheet of high-quality, heavy-weight A4 or Letter-sized plain paper. Do not use photo paper or thin inkjet paper, as they may tear inside the mechanism.
3. Fold the paper in half widthwise (short end to short end), crease it sharply with your fingernail, and then unfold it.
4. Fold one of the outer edges toward the center crease you just made, then unfold it again. This creates a "Z-fold" pattern that increases the surface area of the paper touching the bottom plate.
5. Load this single, folded sheet into the rear tray, ensuring the guide sliders are snug against the paper to prevent skewed feeding.
6. On your computer, go to the printer properties or maintenance menu and select "Bottom Plate Cleaning." If you are using the printer buttons, press the "Maintenance" button (the one with the pliers/screwdriver icon) until the LCD displays the cleaning prompt, then press the "Black" or "Color" button to start.
7. The printer will slowly feed the page through the internal path and eject it. Discard this sheet immediately; it will be covered in black and magenta ink streaks.
8. Repeat this process 2-3 times until the cleaning sheet comes out relatively clean.

If That Didn't Work

• Manual Roller Cleaning: Open the printer cover as if you were changing the ink cartridges. Use a lint-free cloth lightly dampened with distilled water (do not use rubbing alcohol) to gently wipe the grey rubber pickup rollers. If the rollers are slippery, they can cause the page to shift, leading to ink smears.
• Print Head Alignment: If the smudging is actually "misregistration" (where the ink is in the wrong place rather than smeared), perform a Print Head Alignment from the Maintenance tab. This ensures the ink is hitting the paper precisely where the software expects, preventing overlap smudges.
• Cartridge Leak Check: Remove the PG-24 and CL-24 cartridges. Inspect the bottom copper-colored nozzles for "pooling" ink. If ink is dripping from the cartridge, it will contaminate the bottom plate regardless of how many times you clean it. Use a dry paper towel to blot the nozzles gently.
• Hard Reset: If the printer is skipping the cleaning cycle, unplug the power cord for 60 seconds while the unit is on. This clears the volatile memory and can force the printer to re-initialize the paper path sensors.

Heads Up

• Avoid using "Automatic Duplex" settings if you are using heavy cardstock or labels, as these are more prone to rubbing against the bottom plate and causing smears.
• Never use compressed air to blow out the inside of the MG3620; this can push ink droplets further into the optical sensors, causing permanent "Paper Jam" errors.
• Only use genuine Canon ink or high-quality remanufactured cartridges. Cheap third-party inks often have a lower viscosity, meaning they "bleed" more and contaminate the bottom plate faster.
• If you notice the smudging returns every 50-100 pages, your printer is likely situated in a high-humidity environment, which keeps the waste ink "wet" and more likely to transfer to your documents.