HP Color LJ 4700dtn white lines on paper

Hello,
 I got a call for a printer that’s having issues with the yellow toner cartridge only. When printing a PQ Troubleshooting page a white line shows on top of the paper, also the first PQ page (small square box) the yellow color is off the square box. The original problem is that the yellow color comes off margin when the user prints. Although it sounds like is not calibrated I have performed a full calibration many times, about 4 times with the old toner, used a new toner then repeated full calibration about 5 times and still. I printed a test page without the yellow toner (disabled cartridge check option) and it was fine (no yellow color of course). I went to the HP site and did all the troubleshooting as advised and as last resort they ask to contact HP for support but this is not an option for me since I am the tech. I am looking for an advice, maybe something I have not done?
http://www.hp.com/support/clj4700
http://www.hp.com/go/printquality/clj4700
a sample taken from the HP website.
 yellow vertical line to the right
valdezfAsked:
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hdhondtConnect With a Mentor Commented:
Here's a link for the manual. I should have looked at that first before I commented. It appears the 4700 uses a separate laser for each colour. That laser may need to be replace, but I still think it is much more likely its window is dirty. On the drawing showing the laser scanners, the window is on the right hand side of the laser scanner.

http://www.partshere.com/Models/Q7491A/CLJ_4700Theory_of_operation.PDF
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hdhondtCommented:
I don't know the exact internal structure of the 4700. However, it uses 4 toners plus a transfer kit and a fuser. As the transfer kit and fuser are used for all 4 colours, they can't be causing your problem. Hence it's the yellow cartridge, or the yellow laser window. As you've replaced the cartridge, only the laser window is left.

This is where I run into problems: I can't tell you where to look for it. However, it's somewhere in the depths of the printer where it can shine a beam on the drum that's inside the cartridge. I suspect you'll find a little bit of dirt on that window. Remove the yellow cartridge and have a look behind it. You may be lucky and find the problem there.
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valdezfAuthor Commented:
I will take a look at it then post results.
Thanks!
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valdezfAuthor Commented:
Hey, I am looking at the hp 4700 service manual...is the "laser window" same as laser scanner?
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hdhondtCommented:
The laser scanner is the unit that produces the laser beam. It will direct the beam through 4 glass windows onto the 4 cartridges.
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valdezfAuthor Commented:
I might need to replace the laser scanner. I don't have a take apart for the 4700. is there a way you can get this?
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valdezfAuthor Commented:
Hey hdhondt,

 I already have this file in hand. and yes, there are 4 laser/scanners which I might replace the problematic one. The thing is that whichout a take apart (which this file does not have) is going to be really hard to replace.
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hdhondtCommented:
I really think only an experience technician would be able to replace the laser, *and* get the printer working to spec again. Lining up that laser so it converges with the other colours will be a horrendous task.
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valdezfAuthor Commented:
I konw...I am only a PC technician not an expert when it comes to printers...anyways thanks for the advice.
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valdezfAuthor Commented:
I was not able to get a service manual (take apart) for the problematic printer.
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hdhondtCommented:
Begore you replace the laser, have another look at its window, and clean it with alcohol.

You will be able to see the window when you take the cartridge out. The manual makes it obvious where it is: on the drawing it's at the right-hand side of the laser, where it meets the cartridge. To clean it, it's probably easiest to take all cartridges out, so you have more elbow room.
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