Try adjusting the image exposure up as far as it will go. Exposure calibration can also be altered in the 'Additional Functions' menu, under 'Settings & Adjustments'. Settings can be reset to the centre if no improvement is made.
Copies fade out after 18 pages. Toner is not low. when copying in group, copies 16 etc get...
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Copies fade out after 18 pages. Toner is not low. when copying in group, copies 16 etc get progressively lighter in middle of documents