Black lines when printing on aficio 2238

[aaahmmm]

When I print color pages in aficio 2238 after about 15-20 prints I face a black line or lines differ in width , sometimes I stop the machine for a while its print well and then the lines come to appear .

[Vulkor]

Sounds like transfer unit or transfer unit cleaning blade

[Venom]

Replace the K PCU, as it heats up the charge roller gives less charge in areas and black lines appear. The transfer cleaning unit is a possibility but that usually will give Black line on lead edge of rear side that tends go away on a large copy run.