It is possible to have problem with CMY developer drive motor.
its only the BLACK and a bit of cyan color that on the belt
The color patches (CMY) on the belt have the correct densitty (like black)?
It is possible to have defective developer housings or something broken in the IBT assembly.
sure its removed
Are you sure you have removed the shipping covers from the CMY drums?
i had an issue with xerox color c70 that no color output at all ,whether coping or printing .
i attached below the color calibration print out and you can see that C is a bit visibale but M & Y are totally invisible , no problem with Black .
new drums hase been changed , new toners , new belt
anyway i try to made a paper jam and check the belt ,i can see the color on it