Pro C6500 - Vertical lines in print image

[greg0818]

Hi all

I have a strange output. See images attached.
This happens 10-15 impressions into a run, and then stays.
First 10-15 pages are always clear.
Also seems to be predominately biased to one half of the image.

However, when running 50% block tint of C,M,Y & K it doesn't happen at all..?!

We have swapped the following with a working engine. Fuser Unit, Transfer Belt, Drums, Dev Units, Charging Units. Plus have put in a new transfer roller.


Any help greatly appreciated.

Thanks

IMG_0705.jpgIMG_0706.jpg

[Synthohol]

first thing i would do is print the same job in grayscale. see if black is the only color affected.
then zoom the job 150% and see if the problem enlarges as well.
then id put tape over the toner holes of cyan and black dv units and swap them and the drums. (leave toner door open so it wont try to add any) to see if the issue follows the DV unit or just the slot because if the cyan has the same lines its charge or laser related usually for me.