Streaks can come from a dirty inkjet printhead, an ink problem, a laser drum path, or paper handling. Compare a printer-generated page before touching parts.
Print a diagnostic page
Use the exact model's quality report or nozzle check. A stripe on the printer-generated page points toward the printer rather than the source document.
Use the right maintenance
For an inkjet, follow the manufacturer's nozzle-check and cleaning instructions and avoid excessive cycles. For a laser printer, check the documented toner, drum, and corona-wire procedure; keep hands off the drum surface.
Stop condition
If the page shows heat damage, toner leakage, or an inaccessible internal part, stop and contact official service. A cartridge purchase is not a diagnosis.
Official references
Useful next steps
Found a mismatch? Request a correction with the public source URL and exact model, without passwords or full serial numbers.