DIAGNOSIS Black streaks on scanned images indicate dirt or debris on the scanner glass or the ADF's scanning strip.
FIX Clean both scanning surfaces. 1. Lift the document feeder cover. 2. Clean the flat, rectangular scanner glass beneath it with a lint-free cloth and glass cleaner. 3. Locate the narrow, white scanning strip (the moving CIS) along the top of the glass area. 4. Gently wipe this strip with a dry microfiber cloth. Do not use liquid.
IF THAT DIDN'T WORK If streaks are only from the ADF, clean the ADF's own glass strip inside the feeder cover using the same dry cloth method.
HEADS UP The CIS strip is delicate. Never use abrasive cloths or press hard. If cleaning fails, the CIS unit is likely damaged and requires replacement.