Canon ir 3570 not scanning completely

[princepriyu]

i have attached the image for better idea i scanned in the mailbox keeping the door opened,
my machine fails to scan only some part. 8.25 inches from top else works perfect
it scans very faint in some parts it doesn't scan at all

i tried :-
1. changed the platen glass
2. cleaned the lense (Reading Sensor)
3. cleaned and reinstalled the flat cable