the scanner on my 7602 makes a loud thunk and won't move, it's just stuck on the left side.

Diagnosis

The "thunk" sound you are hearing is the stepper motor attempting to drive the scanner carriage (the CIS sensor assembly) against a physical obstruction. In the HP Smart Tank 7602, this usually occurs because the carriage has encountered a mechanical jam or the internal drive belt has slipped/snapped, causing the motor to "bottom out" against the chassis. Because the motor continues to apply torque while the carriage is immobile, it creates a loud knocking or thumping noise. This is frequently caused by a failure to remove the internal transport packaging—specifically the small orange or white plastic shipping locks—or by a foreign object (like a staple or a piece of thick cardstock) sliding under the scanner bed glass and blocking the carriage's rail. To confirm, open the scanner lid and look at the far left edge; if the light bar is pressed firmly against the side wall and does not recoil when the power is cycled, the carriage is physically locked or the drive gear is stripped.

How to Fix It

To resolve the jam and reset the scanner carriage, follow these precise steps:

1. Power down the printer completely and disconnect the power cord from the wall outlet to prevent electrical shocks or accidental motor activation.
2. Lift the scanner lid fully. Inspect the far left and right edges of the glass for any orange plastic tabs or adhesive tape remnants. If you find any shipping materials, peel them away carefully using tweezers.
3. Gently lift the scanner glass assembly if your model allows, or look through the gaps at the sides. If you see a plastic lock mechanism, slide it to the "Unlocked" position.
4. With the power off, place your fingertips on the scanner carriage (the white plastic bar that holds the light). Apply very light pressure and attempt to slide it manually toward the center of the bed. If it moves freely, slide it to the center and leave it there.
5. Check the scanner glass for any debris that may have fallen into the crevice between the glass and the plastic frame. Use a can of compressed air to blow out any dust or small particles from the guide rails.
6. Reconnect the power cord and turn the printer on. The printer will perform a "homing" sequence where the carriage moves to the left and then right. If the thunking stops and the carriage glides smoothly, the jam is cleared.

If That Didn't Work

• Hard Reset the Firmware: While the printer is on, unplug the power cord from the back of the machine. Wait 60 seconds. Plug it back in. This forces the scanner to re-calibrate its "Home" position, which can sometimes clear a software-induced motor loop.
• Check for Belt Slippage: If the motor is spinning (whirring sound) but the carriage isn't moving, the drive belt may have jumped its gear. You will need to remove the outer casing of the scanner assembly to inspect the black rubber belt. If it is loose, reposition it onto the drive gear and secure it with a small zip-tie if necessary.
• Inspect the CIS Sensor: If the carriage moves but then "thunks" at a specific spot, there may be a crack in the plastic guide rail. Inspect the rail for any burrs or plastic shavings that could be catching the carriage. Use a tiny amount of synthetic lubricant (silicone-based) on the rail to reduce friction.
• Factory Reset: Navigate to the printer control panel: Menu > Settings > Restore Factory Defaults. This clears any corrupted calibration data that might be telling the motor to push further than the physical limit of the carriage.

Heads Up

• Never force the scanner carriage with heavy pressure; the CIS sensor is fragile, and applying too much force can crack the glass or bend the internal guide rails, rendering the scanner permanently useless.
• Avoid using WD-40 or oil-based lubricants on the scanner rails, as these attract dust and will eventually create a "sludge" that causes the carriage to jam again.
• Ensure the printer is on a perfectly level surface. An uneven tilt can cause the carriage to bind against the side walls, leading to the thunking sound.
• Keep the scanner glass clean and free of adhesive residue; sticky spots on the glass can actually create enough drag to trigger a "carriage jam" error in the firmware.