HP4100 line feed adjustment creeps?

Hello:
I have 2 identical HP4100 printers and am using pre-printed forms.

Recently, one of these printers began to change the alignment beginning half way down the page: the top half of the page is exactly lined up but in the lower half the print varies vertically from where it should be, anywhere from 0.5mm to 6.0mm. Its like a roller begins to slip half way down the page. (I am accustomed to dot-matrix printers which is why I refer to this issue as a line feed adjustment.)
No jam/misfeed errors are being logged.
The feed and pickup rollers have been changed (2x RF5-1885 & 4x RB1-8957).
I have switched printers and jet-directs: It happens only on this particular printer, affecting 70% of the pages.
There are no print quality issues or fuser streaks.
Any ideas? Could this be a separation clutch/main motor or some other component?
Thanks for any and all suggestions.
-Seepink-

Is it tray related. Can you print the pages from tray 1 without the creep?
Firmware on both printers the same?

does it happen only when you print from the pc or when you print from control panel?

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Originally Posted by redcow

Is it tray related. Can you print the pages from tray 1 without the creep?
Firmware on both printers the same?

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I havent been able to use tray 1 since the door is busted and its taped shut. I will have to investigate the firmware and report back.

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Originally Posted by prntrfxr

does it happen only when you print from the pc or when you print from control panel?

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It only happens from the pc via the jet-direct. I can run 100 copies from the control panel and the registration and print is identical on each copy.
-Seepink-

I would possibly suspect the DC controller ...

Try swapping the JD between printers.

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It only happens from the pc via the jet-direct. I can run 100 copies from the control panel and the registration and print is identical on each copy.
-Seepink-

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dc controller cs_steve? I would be more apt to think network card related than dc controller. especially since the problem only occurs via jet-direct from pc. If there is another reason why it could be dc controller, please tell me. I would love to learn something new.

by testing from the control panel he's virtually eliminated the printer from being the problem. Net card, network settings, pc software issue is more probable.

Well, this is a weird one so I think we're all guessing ... :)
Yes, I would agree with you about the JetDirect being the 1st suspect, but Seepink says he's already tried different JetDirect cards...

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I have switched printers and jet-directs: It happens only on this particular printer, affecting 70% of the pages.

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I was assuming that Seepink tried known-working JetDirect cards -- if that is the case, because this is strangely inconsistent (70% of the time), I would next suspect an unstable DC controller ... since these boards are known for failure ...

Plenty of other possibilities though: faulty scanner? -- these are also failure-prone on 4100's -- or try uninstalling/reinstalling printer driver in Control Panel ... formatter? ...

If you have two of them, I'd swap the registrations just because you can.