LJ4600 that doesn't like black printing

[redcow]

OK, I've got a LJ4600 that prints terrific as long as there is color on the page.
If the user prints straight black text with no color, from the center of the page going to
the right margin the black text fades until it can't be seen when it reaches the right margin.
The center to the left margin is good.
Once you put anything of color on the page (a red "A", a cyan "dot", a colored logo) the black text
is perfect all over the page.
I ran "disable cartridge check" using only the black cartridge(which is a brand new out of the box HP black).
I had the user print the black only document. The o/p is good. I then put each cartridge in one at a time with the
user printing the same document with each insertion. All good o/p.
I then exited out of DIAGNOSTIC mode and let the user print the document again....failure.
If they print greyscale all is good. Greyscale only uses the black.
I need some direction and ideas.

[Big Al]

If it is printing OK from the maintenance panel that would imply that the print engine is working well. That takes us back to the formatter which takes the ASCII code and makes a dot picture. All this sounds good in theory but I have never seen a formatter do something like that. Here we have lots of printers and the luxury of swapping parts to troubleshoot, which you may not have at a custoner's site. The symptoms seem to indicate an electronic problem. Does it do the same thing from various customer computers? When I get something weird like this the first thing I try is reseating the formatter and everything on it three times.

Al

[redcow]

Al, it doesn't matter what PC prints.
I'm gonna try a longshot....have the CU swap the black cartridge out.
They said they swapped it after the problem started, but you know the
axiom "the customer always lies".

[cs_steve]

I would try printing an engine test, that bypasses formatter. First page should be all black lines, see if those lines fade ...

If they do then probably DC controller or laser scanner, if they don't it's either formatter or driver issue.

[redcow]

I can't see it being the laser/scanner, because the disable cartridge test doesn't fail.
And I did plug the cyan into the blacks' slot...no fading.
Also, I plugged my laptop into their network and printed all black with the new cartridge,
and it prints like it should.
The drivers are stored on the server and everytime a PC reboots the drivers are reloaded from the
server. Which makes your driver issue more plausible if the server drivers are corrupted.
Anyways, the CU IT people are supposed to visit the site and check that out.
By the by, I downloaded the drivers off HP's website to my laptop.
I really don't think that I have a hardware issue. Thanks, _steve