The machine is plugged into a dedicated wall socket.
I have reseated the Black toner (where the problem seems to be)
I have reseated the transfer belt/drum
I have reset defaults/NVRAM.
I have run the contamination check.
On the contamination check yellow, magenta and cyan seem fine.
Black has diagonal white lines 3/4 across the page. The last quarter looks fine.
Any ideas what the problem is and how to fix this?
I have several of these printers and this is the second to start doing this.
TIA to all answers