Bizhub c227 no yellow

[1ERIMPRESSIONB]

Hello ,
we have a c227 bizhub that has 5000 pages on it.
there is no more yellow color on any print.
the UI image unit has already been replaced initially but the problem persists with the Next Codes/
-P-33
-P-21
-P28
-P-8
I think code p-33 causes the other codes.
Have you ever had a similar problem?
Cordially

[tsbservice]

Check if yellow IU discharge LEDs are working.

[Todd Glenn]

Any error codes, other than the warning codes, stored under service code history? Have you tried cleaning y laser filter? See if the yellow is getting onto the drum, by stopping mid run.Visually inspect the developer brush, by looking down in between drum and dv unit, on imaging unit, to see if there is still a brush.

[subaro]

wrong post