the scanner makes a loud knocking sound and won't go home when i try to copy something.

Diagnosis

The loud knocking sound occurs because the scanner's CIS (Contact Image Sensor) carriage has lost its "home" position calibration. When you initiate a copy or scan, the printer sends a signal to the stepper motor to move the carriage to the home sensor. If the carriage is physically obstructed or the drive belt has slipped, the motor continues to push the carriage against the internal plastic chassis, creating a repetitive, rhythmic knocking or grinding noise. This is typically caused by a mechanical jam—such as a foreign object falling into the scanner bed gap—or a failure of the drive belt to grip the pulley. In the Canon PIXMA TS6520, the carriage is lightweight and held by a thin rubber belt; if this belt stretches or jumps a tooth on the gear, the carriage cannot reach the optical sensor that tells the printer it has arrived "home," triggering a continuous loop of the motor trying to force the carriage further than the physical frame allows. You can confirm this by listening to the sound: if it is a rapid-fire "thump-thump-thump" specifically from the right side of the scanner bed, the carriage is hitting the mechanical stop.

How to Fix It

To resolve the mechanical jam and reset the home position, follow these precise steps:

1. Power off the printer using the power button and disconnect the AC power cord from the wall outlet to prevent electrical surges or accidental motor activation.
2. Lift the scanner lid fully. Carefully inspect the glass for any debris or small objects that may have fallen into the crevices at the edges of the scanner bed.
3. Locate the scanner carriage (the white plastic bar with the light) under the glass. If it is jammed against the far right or left side, place your finger gently on the carriage and apply very light pressure in the opposite direction of the knock.
4. Slowly and manually slide the carriage toward the center of the glass. Do not force it; if you feel significant resistance, stop immediately to avoid snapping the drive belt.
5. Inspect the drive belt—the thin, black rubber belt located above the carriage. Ensure it is flat, not twisted, and seated firmly on the pulley wheels. If it has slipped off the gear, use a plastic tool or a blunt pencil to gently guide it back onto the sprocket.
6. Once the carriage is centered and the belt is aligned, reconnect the power cord.
7. Turn the printer on. The printer will perform a "homing" sequence where the carriage moves automatically to calibrate its position. If the knocking stops and the carriage settles at one end, the issue is resolved.

If That Didn't Work

• Perform a Hard Power Reset: With the printer on, unplug the power cord directly from the back of the unit. Wait exactly 60 seconds to allow the internal capacitors to discharge. While unplugged, hold the power button down for 15 seconds. Plug the unit back in and restart. This can clear "ghost" errors in the firmware that keep the motor running.
• Clean the Encoder Strip: If the carriage moves but still "hunts" for the home position, the thin transparent plastic strip (the encoder strip) running parallel to the carriage may be smudged with ink or dust. Use a dry, lint-free microfiber cloth to very gently wipe the strip. Avoid using alcohol or cleaning fluids, as these can erase the microscopic timing marks.
• Check for Chassis Warping: Inspect the plastic frame around the scanner glass. If the printer was dropped or hit, the frame may be slightly bowed, pinching the carriage. Apply gentle pressure to the outer casing to see if the carriage regains free movement.
• Factory Reset the Device: Navigate to the OLED display menu: Setup > Device Settings > Reset device. This forces the printer to re-initialize all hardware components, including the scanner motor calibration.

Heads Up

• Avoid Manual Force: Never pull the scanner carriage with significant force. The drive belt is thin and can easily stretch or snap, which requires a complete teardown of the scanner assembly to replace.
• Keep the Lid Closed: To prevent dust and debris from falling into the carriage track, keep the scanner lid closed when not in use. Even a small piece of paper or a staple can jam the CIS carriage.
• Power Cycle Sequence: Always power down the device via the button before unplugging it. Cutting power during a carriage movement can lead to corrupted calibration data in the NVRAM.
• Surface Stability: Ensure the TS6520 is on a completely level surface. An uneven tilt can cause the carriage to slide slightly off-axis, increasing friction and leading to the knocking sound over time.