Print fading on left side

[ScrewLoose]

I have 2 LaserJet M402dn printers that are doing the identical problem.
 they print nothing on the left side, and the right side is fine. its and even transition between the 2 sides, meaning printing the Demo page from the printer panel produces a sheet that is total white on the left edge to a perfect demo sheet on the right edge. 
 So far, I have swapped toner cartridges with other printers (We have a couple dozen of these printers).
 I installed a new Fuser, in 1. Neither of these made any difference. The printer still output the exact same thing with different toners and a different new fuser.
I am totally stumped as to what to do next.
Any recommendations?

[Guy-1]

If you have changed the toner and the fuser,  check the transfer roller is located correctly at both ends of the roller.  (long roller that sits below the toner cartridge)

[east2100]

What you said has nothing to with fuser which fuser will never act like that.

It may have something to with transfer roller which seats under the cartridge. Check it first to see if it seats  right or not, may be the left side is out of its place or somehow.

Another problem may is the scanner itself. Check to see if something got block in the way of laser ray, most of the time it may has a broken piece of paper is there. if the width of blank area will change or change from left to the right or change one place to another, then you may have cockroach(es) live in the scanner which you need to clean them up.

[ScrewLoose]

The transfer roller appears to be fine. It is seated like normal and has spring tension on both sides.
I do not have a new roller yet, but I removed it, and flipped it, with no change to the print output.
I am curious about what East2100 presented about the scanner.  I was not aware this model has a scanner, but maybe I am wrong? Maybe its internal? where would I find it if so?
I should note these printers are in a weld shop production environment, it is clean for this kind of work, but still dirt in the air.
so I wondered if it could have drawn dirt into the left side of some optical device?  taking a stab in the dark on that.

[east2100 · Accepted solution]

The scanner's full name is Laser scanner assembly you'll need a Repair Manual google and download it.

It seats between the top of toner cartridge and under the top case.

[ScrewLoose]

Just so everyone knows, The scanner had a layer of dust on the glass that was thicker on the left side.
I cleaned the glass and it works like new again.
 

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