I have a CM4540 that got a new fuser drive unit. What a job. After the job, I was printing out test pages, and suddenly, in the middle of it all, they started turning solid yellow in the background. I checked all the connections, and everything seems good. Then I saw on the formatter interconnect board, that a couple of the metal contacts on that ribbon cable were loose and folded out. I tried fixing it, but finally replaced it. Eveything else works now, but, except in colored prints, all yellow background...except the edges. The edge-erase is working fine. All edges are white. I ran an engine test, and those print fine--no yellow background.
I guess I know the answer to this--the formatter. But I'm hoping someone knows something I don't. I don't feel like going to the customer and telling them they need to spend another $300.