So this is the product that comes out of our Xerox Phaser 7500 DT, which is now 2 years old. It's not a problem caused by the fixing unit, we just ordered a new one and the printing result is the same. Once we had a technic ordered who calibrated the printer, so there were some options made by a professional. I was hoping that someone had the same problem and could tell me what I have to do, to make it work constantly fine again. As it's said in the topic: the problem only appears when dark colors are used. If you need any more Information about the settings that were made, please ask specifically because my knowledge about this printer is not very advanced.
thank you very much!