8R1U-01K
Streaks that are parallel to the direction of feed appear in the printout
The corona assembly wires inside the main unit are dirty. Clean the wires.
← Feeding Direction
Remedy
Clean the corona assembly wires inside the main unit several times.
Press 
→ <Adjustment/Maintenance> → <Maintenance> → <Clean Wire>.
→ <Adjustment/Maintenance> → <Maintenance> → <Clean Wire>.
"Settings/Registration" > "<Adjustment/Maintenance>" > "<Maintenance>" in the User's Guide > see the subsection "<Clean Wire>"