C220 Gradation problem in black only

[AjitN]

Hi all
Customer called for very light Cyan cast on prints, especially on thick media & also white lines in black.
Cleaned black developer Assembly for white lines in black and cyan drum unit for toner contamination.
Page no 1 test page is after above activities. 30529
Cyan cast was still there on thick media. So interchanged cyan & yellow drum unit. Machine gave me error "Wrong Drum unit in Cyan'. Cleaned drum detection contacts & Drum Chip and machine sensed cyan Drum unit.
Now real problem popped up. Black suddenly gone very high & in gradation scale on the test page 100 to 40% it is 100% black patch & 30 to 5% it is ok. Of course image also very dark. See page no 2. 30530
Performed Initialized & Stabilization then gradation (twice ), Replaced Black Drum Unit. Cleaned Black Developer unit & Bias contacts. No change in copy, Prints.
Looks like PH unit is not able to write black gradation properly. So it could be PH unit, Ph Relay Board, Prcb etc.

Anybody faced such problem? Any suggestion before I start replacing parts.
Thanks in advance for all, any suggestion.

[AjitN]

Surprising No suggestions, No feedback, no comments.

Does it show that nobody faced similar problem world wide.
really badly in need for some suggestion.

Regards & Thanks

[allan]

Hi, the only time i get light tones on the prints is if the drum is shot(charge dirty).
If you swap the drum units u can change between colour and B/W with out also changing the chips around.

Change the Black developer unit for the black problem.