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The diagnosis for this problem will differ, depending upon whether the white line is present on Photocopies, or only on Printouts sent from a computer, or on both.
White lines are usually caused by either a defective scanner sensor or a defective scanner bulb... or else, more usually, by a clog in a toner cartridge, or even linear damage upon a fuser unit.
A further detail of importance is whether the white line interrupts all colors (in a color laser printer) or only one color (in a color laser printer)... it can't be a fuser damage problem, if only one color is interrupted or affected.
Examine the problem according to what I've just explained, and let me know which of these it is, and I will advise you accordingly.
The scanner unit is - on laser printers equipped with photocopying capability - the part that moves under the glass sheet during a photocopy on that same glass sheet.
The CL3000 of course, has no photocopying capability. The white line of missing toner, is most likely either from a defective toner cartridge, or else from a damaged fuser roller, depending upon whether it interrupts only one color, or all colors (-all colors missing, means a damaged fuser, most usually. The fuser is a heated part with several rollers at the end of the paper path, since fusing is the last stage in laser printing.
(I regret that I am not able to offer Live Phone Call service at this time; However, your request is still open to other Experts in this category, and one of them may pick up on it at any time.)
Does the white line constitute interrupted toner, of all colors? try printing a full-color sheet, to see.
If so, the developer or 'drum' may have a damaged stripe upon it. That, the drum, is easily damaged. Such damage should show at a glance.
Note that 'drum' damage usually shows a slight repetition down the page at intervals of the circumference of the drum.
Another possible thing: toner spills upon the corona wire. Cleaning the corona wire, now usually included in toner cartridges, by moving back and forth the small colored-plastic tab on the toner cartridge, should eliminate the white line of missing toner, if that's what is causing it. (And that would be the case where toner is missing in one color but not others, most likely.)
It is contained within the cartridge in most modern laser printers.
Look on the cartridge, removed from the printer, for a colored plastic tab, that slides to and fro. Bright green, or sometimes orange. Slide it to and fro along the full range, letting it stop at one end of its range. That cleans the corona wire.
Check the 'drum' then - for the black color.
It should be brightly metallic-looking, sort of blue-green-metallic-shiny, and be warned, it is very easily damaged by touching, wiping, getting wet, abrasion, exposure to more than 1/2 minute of light per half hour, etc.
If it has a worn-off band on it, in the same position as the white line, then replace it.
Have you found and examined the photosensitive 'drum' for the black section of the printer ?
Did it have a band of damaged surface on it, corresponding to the 'white stripe' that you have asked about, on the printouts ?
Or... is the problem solved, by other means, perhaps?
Please let me know. Thanks.