Phaser 550 colors not converging properly

[ven0m]

The colors (CMY) are converging just fine. At the top of the page Black converges very closely with the colors (maybe just barely above but not enough to bother me) but by the bottom of the page the Black is about 1 to 2 mm to high (towards the top of the page). It does this on everything, even test prints that stack colors (like the menu map print), problem does not come and go either, it seems to be here and it is identical every page.
For kicks tried replacing the toner as I had a new K toner allready. Of course that was no help. So the only thing left that is involved with the transfer of colors is the Imaging Unit. But before I shell out large cash for one of those when this one still shows under 50% used I was hoping there is something else that may be causing this. I can't really see why all the colors would converge fine except for black, that makes it hard for me to justify the IU as a culprit. I can tell that black is put on the IU first, then CMY with each IU pass, but I wonder if may the IU's belt speed is off until it gets cranked around a revolutiion or something.

Any ideas?

Thanks for your time!

 

[web2web]

Before replacing the Imaging unit, make sure that the imaging unit belts are tensioned and in the locked position.

Unlock the large, blue knob in the middle of the Imaging Unit.

Slide the Imaging Unit out of the printer half way, then firmly reseat it.

Tighten all three blue knobs so that the arrows all line up.