my canon pixma ts6420a is making a horrible grinding noise when it prints, like it's chewing something

Diagnosis

The "chewing" or grinding noise in a Canon PIXMA TS6420a typically indicates a mechanical failure in the carriage drive system. Specifically, this happens when the printhead carriage (the assembly that holds the ink cartridges) cannot move smoothly along the horizontal metal rail. The noise is caused by the plastic gears of the carriage motor slipping or skipping teeth because the carriage has encountered a physical obstruction or is experiencing excessive friction. This is most commonly caused by one of three things: a foreign object (like a scrap of torn paper or a fallen paperclip) lodged in the carriage path, a buildup of thickened, dried ink on the encoder strip—the thin, clear plastic strip that tells the printer where the head is located—or a lack of lubrication on the carriage rail. If the encoder strip is dirty, the printer "loses" the position of the head, causing it to slam into the side walls of the chassis at full speed, creating that violent grinding sound. You can confirm this by opening the scanning unit and attempting to gently slide the carriage by hand; if it catches or feels "gritty" at any point, you have a mechanical blockage.

How to Fix It

Perform these steps in exact order to clear the obstruction and reset the drive system:

1. Immediate Power Down: Press the Power button and then unplug the power cord from the wall. Do not simply use the standby mode, as the carriage may attempt to "home" itself and cause further gear stripping.
2. Clear the Path: Open the main scanning unit/cover to expose the interior. Use a high-intensity flashlight to inspect the far left and far right "docking" areas. Look for small scraps of paper from previous jams or foreign objects. Use a pair of tweezers to remove any debris.
3. Manual Carriage Glide: Gently grasp the printhead carriage and slide it slowly from the far left to the far right. If you feel a hard stop before it reaches the end, do not force it. Look for any skewed plastic guides or displaced springs.
4. Clean the Encoder Strip: Locate the thin, transparent plastic strip that runs horizontally across the width of the printer behind the carriage. Using a lint-free cloth dampened slightly with distilled water (no alcohol), very gently wipe the strip from one end to the other. Be extremely careful not to pull the strip out of its tension spring.
5. Reset and Test: Plug the printer back in and power it on. If the noise persists during the initialization "homing" sequence, power off immediately and check for ink leakage on the rail that may have created a sticky residue.

If That Didn't Work

• Inspect the Paper Feed Rollers: Sometimes the grinding noise isn't the carriage, but the pickup rollers slipping on a heavy cardstock or skewed paper. Open the rear tray and check for any debris trapped in the feed mechanism. Use a damp, lint-free cloth to clean the rubber rollers to ensure they aren't slipping and causing the motor to strain.
• Check for Cartridge Misalignment: Remove all ink cartridges and ensure the plastic tabs are fully clicked into place. If a cartridge is slightly protruding, it can snag on the internal chassis of the TS6420a, causing the motor to grind as it tries to push the carriage past the obstruction.
• Lubricate the Carriage Rail: If the rail feels dry or "scratchy," apply a tiny amount of high-grade synthetic grease (like Super Lube) to the metal rod. Do not use WD-40 or vegetable oil, as these will attract dust and degrade the plastic components over time. Wipe away any excess grease so it doesn't drip onto the encoder strip.
• Hard Hardware Reset: Unplug the printer and hold the power button for 30 seconds to discharge the internal capacitors. Plug it back in and immediately perform a "Power Cleaning" from the maintenance menu to ensure the carriage is moving through its full range of motion without resistance.

Heads Up

• Avoid Force: Never force the printhead carriage if it is stuck; the plastic gears on the TS6420a are fragile and stripping a single tooth can render the entire chassis irreplaceable.
• Ink Management: Avoid using third-party "remanufactured" cartridges that leak; leaked ink on the carriage rail is the primary cause of the "gritty" feeling and subsequent grinding noises.
• Environment: Keep the printer in a dust-free environment. Dust accumulating on the encoder strip causes "ghosting" prints and carriage positioning errors.
• Paper Quality: Only use paper that matches the settings in the print dialog. Using heavy cardstock in the standard paper tray can cause the rollers to slip, mimicking a carriage grinding sound.