Loss of black print

[atiq]

I have a KM C220, which I'm having a problem with the black print when I try and print a black copy nothing comes out on black. I have done a graduation adjust and CMY come out perfect but no black print.

We changed the toner hopper - k toner - image drum - laser unit even the cogs that turn the k toner drum.

I'm total baffled by this one.


Atiq