I have an Officejet Pro 6830 printer.
Lately, when I scan a document from the automatic document feeder, I get a thin black line from the top to the bottom in the middle of the scanned document (see the attached photo)
I raised the cover and tried to clean the parts the move the document, but that didn't help.
The problem does NOT occur when I put the document on the glass
Any idea?


Cleaning scan glass strip of vertical lines:


The issue may be caused by a small spec on the ADF scanner glass, (the thin glass to the left of Flatbed scan glass)

This sensor is used for both the flatbed scan and the automatic document feeder (ADF), the difference is where the sensor is moved to for scanning. When scanning from the flatbed the sensor moves across the bed, a spot in this area will result in a spot on the page. When using the ADF the sensor is moved to the thin glass to the left of the main bed, and the paper is moved past the sensor by the ADF. A spot in the wrong place here will result in a line down the length of the long side of the page. Clean this areas as shown below.



Figure : Locate any debris on the ADF scanner glass strip





If the initial cleaning does not resolve the issue it may help to shine a bright flashlight nearly parallel to the glass. For a line on the left side of the printed page the spot will be toward the front of the printer, if the line is on the right of the paper it will correspond to a spec toward the rear of the printer.


Figure : Clean the ADF scanner glass strip






This resource will be useful:

HP AiO Printers : Resolving Vertical lines or bands on copied or scanned document