That is common problem for this type (l3150, 3110, 3210) this problem cause by:
# Improper scanner attached to its pin.
# Hard stuff/heavy stuff felt down on to the scanner.
# Dust accumulate on the scanner tract.
Solution:
# Check ribbon scanner cable, whether it is torn uuo or not.
# Dissemble the scanner and clean the track, while repositioning the scanner correctly (don't miss even half millimetre).
Hope this will answer your questions.