Xerox DC 700, white spots in all colors, only with larger formats

[JulianMue]

Hello,
does anyone know the following problem with a Xerox DC 700: White, non-uniform spots or no color application in all colors at the end of the printout (left side). The problem does not occur with DinA4, only with larger formats. I've already swapped: IBT Belt, Charge Corotron. Lasers are cleaned.
Thanks!

[xcopytech]

Replace 2nd btr assy

[JulianMue]

Thanks a lot! it worked!