If the black line shows up when copying from the glass AND when using the document feeder then it is not the strip glass. Is it a fine line or a wider band like say 1/4 inch or larger? If it is larger then it is most likely the drum cleaning blade. You can verify it is a blade by running say 10 copies in a row. If the line gets worse as it runs copies it is the blade. Of there is no line when using just the glass then it is something on the strip glass or scan glass.
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If the black line shows up when copying from the glass AND when using the document feeder then it is not the strip glass. Is it a fine line or a wider band like say 1/4 inch or larger? If it is larger then it is most likely the drum cleaning blade. You can verify it is a blade by running say 10 copies in a row. If the line gets worse as it runs copies it is the blade.
Of there is no line when using just the glass then it is something on the strip glass or scan glass.