Could the white line be due to clumping in the yellow developer? if so, do you know if we can replace the developer powder (seems to be about £75 online)? or where do we find an engineer to do it?
It should be the yellow imaging unit, and since it is an absents of color, I would guess physical damage to it, so just pop it out and have a look, likely there is something visibly wrong with the roller.
You could even swap yellow for another color to see if the issue moves to the color you swapped with, but it would take about 10 copies to be sure it did or did not.
Hi, our Phaser 7800 has suddenly started outputting a faint white stripe along the page (not across the print left to right) A cymk test page shows it only on the yellow, not cyan magenta or black. The line is about 5mm wide, slight faded edges to it. Looks about 50% yellow so not white as such.
Some info: about 2 years old, just 33,000 colour impressions, 1,000 black impressions, all original replaceable parts still at approx 75% life from new, never replaced (except toner of course).