Black edge on copies?

Have a Sharp AR162 that makes a 2 to three inch black background threw the entire copy on one edge. It only does it threw the doc-feed. Under the platen glass copy is normal. Clean slit glass & etc. There looks like two sensor units 1"x1" under the platen glass. Wondering what they are for or if one is bad or is for doc-feed. Experience on other copiers but not on this sharp model. need help-thanks - Lloyd