the scanner on my pixma tr8620a makes a loud grinding noise when it tries to scan, sounds bad.

Diagnosis

The loud grinding noise in your Canon PIXMA TR8620a is caused by a mechanical failure in the scanner carriage assembly. Specifically, the stepper motor is attempting to drive the CIS (Contact Image Sensor) unit along its horizontal rail, but it is meeting physical resistance. This results in the gears slipping or "chattering," creating that harsh grinding sound. This typically happens when the lubricant on the carriage rail has dried out or become contaminated with dust, increasing friction to the point where the motor cannot overcome it. Alternatively, the noise is often caused by a "home position" failure. The scanner carriage has a small plastic gear and a timing belt that align the sensor. If a foreign object—such as a staple, a small piece of torn paper from the ADF, or a buildup of grime—enters the track, the carriage jams. When the printer initiates a scan, the motor continues to spin against the obstruction, causing the plastic gears to strip or grind. You can confirm this by attempting a "Copy" command; if the noise starts immediately as the light begins to move, the issue is strictly mechanical within the scanner bed.

How to Fix It

To resolve the grinding noise and restore smooth movement to the scanner carriage, follow these precise steps:

1. Power down the printer completely and disconnect the AC power cord from the wall outlet to prevent electrical shock or accidental motor activation.
2. Lift the scanner unit cover and open the Automatic Document Feeder (ADF) tray to gain maximum visibility of the internal chassis.
3. Carefully lift the scanner glass assembly if your model allows, or look through the gaps of the ADF. Locate the white plastic scanner carriage (the light bar) located beneath the glass.
4. Gently and slowly slide the scanner carriage by hand from its resting position on the right side toward the left. If you feel a "catch" or a hard stop, use a flashlight to inspect the rail for debris, such as staples or plastic shards.
5. Use a can of compressed air to blow out the metal guide rail and the gear assembly located on the far right side of the scanner bed.
6. Apply a pea-sized amount of white lithium grease (do not use WD-40 or liquid oils, as these degrade plastic) to the metal guide rail. Use a cotton swab to spread the grease evenly across the length of the rail.
7. Manually slide the carriage back and forth three times to ensure the lubricant is evenly distributed and the movement is fluid.
8. Close all covers, reconnect the power, and perform a "Scanner Calibration" or a simple black-and-white copy to verify the noise has ceased.

If That Didn't Work

• Inspect the Timing Belt: Check the small rubber belt that connects the stepper motor to the carriage. If the belt has slipped off its pulley or has a visible tear, the motor will spin freely (grinding) without moving the carriage. If the belt is loose, you will need to remove the outer casing to reseat the belt on the drive gear.
• Check for ADF Obstructions: Sometimes the grinding isn't the scanner bed, but the ADF rollers. Open the ADF cover and look for a jammed piece of paper stuck in the pickup rollers. If the ADF is trying to "pull" paper while the scanner is moving, the dual-motor strain can sound like a single grinding noise.
• Reset the Home Position: If the carriage is stuck in the "wrong" spot, the printer may panic. With the power off, gently push the scanner carriage all the way to the far right (the home position) until it clicks. Power the unit back on; this often allows the sensor to find its zero-point and stop the grinding.
• Replace the CIS Unit: If the noise persists and the rail is clean, the internal plastic gears of the scanner motor assembly may be stripped. In this case, the entire scanner carriage assembly (CIS unit) must be replaced as a single module.

Heads Up

• Avoid Heavy Lubricants: Never use automotive grease or heavy oils on the scanner rail; these attract dust and will eventually create a "sludge" that jams the motor permanently.
• Glass Care: When cleaning the scanner bed or applying grease, be extremely careful not to scratch the underside of the glass, as this will create permanent streaks in every scan.
• Power Cycle First: Always perform a hard reset (unplug for 60 seconds) after a mechanical jam to clear the "Error Code" from the printer's temporary memory.
• ADF Maintenance: Periodically clean the ADF rubber rollers with a damp, lint-free cloth to prevent paper jams that can put undue stress on the overall chassis alignment.