8R1U-01H
Streaks that are perpendicular to the direction of feed appear in the printout
The intermediate transfer belt is warped. Clean inside the main unit several times.
← Feeding Direction
Remedy
If you have not used your machine for a long period of time, the intermediate transfer belt may become warped. If this happens, clean inside the main unit several times.
Press 
→ <Adjustment/Maintenance> → <Maintenance> → <Clean Inside Main Unit>.
→ <Adjustment/Maintenance> → <Maintenance> → <Clean Inside Main Unit>.
"Settings/Registration" > "<Adjustment/Maintenance>" > "<Maintenance>" in the User's Guide > see the subsection "<Clean Inside Main Unit>"