on my all-in-1 HP Officejet 4650, when i either scan or copy using the feeder on the top of the printer, i get a thick grey line down the middle of the page. this occurs on the printed page and on the screen. when i print from my computer, this problem does not exist. when i use the "face-down" method of copying, this problem also does not exist.
There is contamination on the slit glass that the automatic document feeder uses when scanning. Lift the ADF lid and examine the glass at the far left. The way scanners read information, even the tiniest amount of opaqueness can cause defects. If you lay a copy with the defect on the glass, face up, it should show you exactly where you need to clean.
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