The scanner makes unwanted vertical lines down the document

I suspect the Document Feeder is not aligned properly and light is leaking in. You will need to have a technician in to check the alignment of the scanner to see if it needs to be readjusted. random black lines on edges usually indicate light leaking into the scan area.

Probably there is nothing wrong with that scanner, just open and clean document feder with alcohol or glass cleaner.

Check your flat bed and Document feeder scanning glass need to be clean, if any dot or dust in scanning glass of document feeder it will appear a line, check this points first
1- Check printouts from computer or FAX if it is clean problem in scanning section
2- Check using Copying a blank paper using only Flatbed if it prints without any line its problem from document feeder Scanning glass
So solution is clean the Document feeder scanning glass using wet cloth, note careful about wet cloth switch off the machine and clean it

Its dirt! It takes just one tiny speck of dirt on the lens to make a vertical line.

We have some scanner maintenance videos;you want to clean the CIS front sensor.

Regards,

MyEfact

you have a problem in your scanner assembly, clean or replace it

happened to me after i fed a page with not-too-hard whiteout on it. the feeder makes the page run through a different piece of glass and i just had to clean it.

the problem is in the scanner, open it up and see if you can find any smudges, and clean any obstruction, any ink, liquid eraser residuals, can cause this part to appear as lines on your copied faxed image.
dont concentrate on the printer this is a scanner problem

Lift the lid and to the left of the main glass is a smaller glass; that is what scans during the feeding process. Make sure that it is completely clean; even a speck of dust can cause a line to appear. I took a lens wipe and cleaned mine and my line was gone.

Some dust particle or something might have been stuck on the scanner. Try cleaning the scanning glass

Clean the glass with IsoPropyl Alcohol. Dont use any other solvent. A speck of dust stuck to the glass can give a continuous line in the output

S. Mohan