Bizhub C6500 problem with black

[alabovic]

Hi guys,
I have problem with black color, like it is "washed out" with so many lines.
Also there is a bad registration especially at the end of the paper.
I changed the developer but after that I couldn't execute automatic colour registration in service mode with C2804 error.
And result is the same. Nothing changed.

Pictures attached

Dropbox - Untitled.pdf - Simplify your life (https://www.dropbox.com/s/dfz740gsle4a9xe/Untitled.pdf?dl=0)

Any ideas?

[Synthohol]

i like swap isolation.
put tape over the feed hole on the black and cyan DV units and swap them. swap the respective drums too. leave the toner door open during testing so it wont try to add any.
if the issue follows black its a bad DV unit. if it is now a cyan issue its a laser/charge/processing problem but at least you eliminated the DV unit and the drum as the culprit.

[raplma]

I would also look at checking how clean the machine is inside.
Clean the colour registration assay, which is where the PGC sensor lives which is linked to the c280x codes, the 4 referencing black - no surprise.
Also check the drum potential sensors, they regularly get misted in toner etc.

[tsbservice]

Just a small supplement to other guys valuable advices, if you give a valid email I can send you useful troubleshooting guide for this model.