Solution:

To identify the affected color, print three full-page, solid-fill A3 or DLT sheets for each of cyan, magenta, black, and green, and three full-page, halftone A3 or DLT sheets for each of cyan, magenta, and yellow.

Because it is difficult to identify white spots on yellow, green is used instead of yellow.

Detach the photoconductor unit of the affected color and check the drum surface. Is the surface stained?

Yes

Wipe the photoconductor unit surface with a clean dry cloth to remove the stain. Then in the 05: [Machine: Maintenance] group on the [Adjustment Settings for Operators] menu, select the affected color and execute 0501: [Execute Cleaning Initial Setting for PCU].
In the 02: [Machine: Image Quality] group on the [Adjustment Settings for Operators] menu, select 0201: [Execute Image Quality Adjustment] and execute [Adjust Image Density].

Replace the photoconductor unit.

Print the image. Has the problem been resolved?

Yes	Finished!
No	Replace the PCU cleaning unit and photoconductor unit.

If the problem persists, contact your service representative.

For details about replacing the PCU cleaning unit and photoconductor unit, see Replacement Guide.