canon ir 400 print problem

[regalcopy]

white line comes (matter doesn't prints) in print in one fix place in copy. this is like straight white line from start to end.
i've checked drum unit, toner supply, laser (checked from other machine) as well.

pls advise me

[JayP.]

run a copy ,stop copy when the paper get under the drum ,is the print missing on the drum, check the mirrors for objects blocking you light ,check for object blocking your laser to the drum . hope this helps .Jay.p

[SCREWTAPE]

Check your transfer roller