Fujitsu fi-7800 Operator's Manual page 55

Move the hopper side guides towards the center as you press the side guide clutches, and leave no space
between the hopper side guide and the widest document.
4
Lock one of the hopper side guides.
In this case, lock the hopper side guide on the right side by sliding up the side guide lock.
5
Move the other hopper side guide to the target position while pressing the side guide clutch.
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How to Load Documents