That is common problem for this type (l3150, 3110, 3210) this problem cause by:

1. Improper scanner attached to its pin.
2. Hard stuff/heavy stuff felt down on to the scanner.
3. Dust accumulate on the scanner tract.

Solution:

1. Check ribbon scanner cable, whether it is torn uuo or not.
2. Dissemble the scanner and clean the track, while repositioning the scanner correctly (don't miss even half millimetre).

Hope this will answer your questions.