Change the pickup roller, sep belt and reverse roller. A slick sep belt and/or a worn out reverse roller will give misfeed problems. ALso, keep your original stack below the line on the original feed guide.
yeah am thingking also the paper limit that ADF for this model can feed in. maybe too much paper original. but as mention above cleaning the sensor and replacement of pick-up, separation and feed belt....
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fix the customer first then fix the machine... its simple and makes life more easy.
I have run across this issue a couple of times.
Try standing to the right of the machine and look under
the ADF cover(while it's closed). See the pickup roller
sitting under there. Is it sitting level or is it cocked down
just a little towards the back. If it's not level the black
plastic assy. that holds the pickup, feed rollers and feed belt
has been damaged. It usually cracks where the springs push
against the right feed belt axle. There's a small finger that
keeps the feed belt axle in place and gets broken when people
raise the assy. vertical to clean or remove paper then accidently
shut the lid without laying down it back down first. I keep
one in the car at all times. I think the same part works starting
with the Af350 and is still used in the AF3035 series.