Try (you with your tech of course) to move the MCU PWB from one machine to the other one.
At first I would think the banding would be related to a fuser issue, however, with the connection issue you describe, it might be a hardware issue. I would recommend contacting the Support Department. The Support Options for your device are listed HERE.
Have 2 D125's in a school print shop. "New" machines, in place about 7 months. Both @ 900k
One is working perfectly. The other, has a CQ issue. Vertical bands (sky shot, lead edge to the right,
partial sky shot).
Intermittent, sometimes you may get 50-200 w/o any issue. I went with the tech that has been
working on this problem and what we did was take the drum, developer unit, transfer belt assembly,
and placed them into the working machine, and the CQ problem did NOT move to the other
machine, so we are certain the problem is not a drum/developer/transfer belt problem.
We then pulled the back cover, to access the HVPS connections to reset them. Upon removing
the cover, we found the rear frame has been impacted, bending the connections to the scanner
and the rear is caved in, but, there is NO damage to the rear cover. After we discovered that,
we remembered when he had to replace the laser ROS unit, that the alignment pins that hold
the scanner in place, one of them was broken from the weld spot on the frame.
After removing the HVPS, and reseating all connections, the problem remains.