Fujitsu FI-7160 scan black getting color image

[gideon]

When scan black and white on black scan setting the image is black.

When scan black and white on color scan setting the image is color.

This is only on side 1 of scanning, side 2 is normal ( When scan black and white on color scan setting the image is black on side 2).

Any idea?

Service manual for this model?

Thanks