Hp color laserjet cp4020 series black printing too light

Question

Our company bought an HP Color LaserJet CP4025 about 2 months ago.  It printed perfectly through our first deadline, but when we changed the black toner cartridge, it now prints somewhat brown or gray and the colors aren't quite as bright.  What can we do to fix this?

Answer 1

So the other colors are printing darker / or look normal?  If Only the Black is faded even on the config page relative to the other colors present, or in other documents?
Do you have another cartridge to test out if this is a cartridge issue?
In the Service manual it indicate the if print is light or faded in a particular color there may be a poor primary transfer bias contacts on the ITB unit and product, or porro primary charging bias contacts with the print cartridge and product, or poor developing bias contacts with the print cartridge and product
Solution: Clean the contacts of the color that produces the light print.  If the problem remains after cleaning check the contacts for damage.  Replace any deformed or damaged parts.
http://www.scribd.com/doc/77359204/CP4020-CP4520-Service-Manual#outer_page_60
I work for HP