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HP COLOR LASERJET PRINTER 4600 IMAGE DEFECTS

Updated: Jun 7, 2019

Recently, some customers contacted us with similar questions about the CLJ 4600. Both had CLJ 4600 printers that were spitting out blank pages or color pages without black.


We’ve seen color issues in other older color units such as the CLJ 5500. The CLJ 5500 would have degrading or incorrect colors. One was a mechanical failure with a defective ITB belt, and the other program code that was easily fixed with a RFU (Remote Firmware Upgrade).


The older HP color laser printers would occasionally have a problem with the E-clip of one of the ITB arms resulting in one side of the intermediate transfer belt dropping away from the image drum. When this happened color would not transfer across the gap on the one side, but the black toner did.


This was due to the chemical make up of the black toner which was mono component, while the color toner was chemical toner. The magnetic properties of the mono component or magnetic black toner allowed the transfer to take place while the non-magnetic color toner could not.


The toner in the CLJ 4600 and CLJ 4650 printers use chemical, non-magnetic toner so we need to eliminate this possibility. So, what would cause a color print to have just the color on it but no black? White page, lots of possibilities, but color page and not black print?


The Developing Process This goes back to how the image is developed in the toner cartridges and ultimately how the transfer belt is cleaned. On the CLJ 4600 series, each

toner cartridge is a clam shell type set up.


The opening and closing of this clam shell is actuated by alienation bars behind the toner cartridges. This actually engages and disengages the developer roller with the image drum. If the clam shell is set with the developer roller to be disengaged during the creation of a print, the result would be no print, or a blank page. OK, that makes sense, and even explains the blank pages. But how could this create a color print with no black on it?


While the CLJ 4600 and CLJ 4650 units are considered color printers, they are also set up to produce monochrome-only prints using just the black toner cartridge. When the printer is producing a black page only, the color developers are disengaged.


The black alone is engaged which produces the print. While we could have chosen to leave the color developers engaged and not write an image to the color toner cartridges, the toner developers have a monitored life to them.


If the color developers are engaged on a monochrome print, a life count is added to the developers even when they don’t create an image. The end result can be a color toner cartridge at end of life with a lot of unused toner still in it. For those of you who have customers wondering why they are replacing color toner cartridges on a regular basis but not printing much color, this could be a clue.


How Can The CLJ 4600 Create a Color Print With No Black Toner on It? Theoretically these machines could use just the color toners to create black on a page. This would be done by using all three colors, one right over the top of the other – this is called composite black. However, in real life, this is not a true black – it tends to be more brownish.


Thus on all color prints, the black toner cartridge developer is engaged to help out with the black on the page. The only time the black toner cartridge developer is not engaged is when cleaning is done. In this instance, both color and black developers are disengaged by the alienation bars.


This allows for toner or impurities on the belt to be removed by attracting it to the image drum and dropping it in the waste toner area of the cartridge. This is also done during the calibration process when color swatches and timing marks are physically written to the transfer belt to be checked for accuracy.


These physical writings need to be removed from the transfer belt or it will show up on the back of your printed pages. If the alienation bars, which engage and disengage the developers, get stuck in one position, say the disengaged position, the result is no development of the written image. And you have a page without that particular color.


The color cartridges use one set of alienation bars to engage and disengage the developers and the black uses a separate set. The black alienation bars are most often the ones that get stuck which would explain the loss of black print on a color page.


Laser Printers With Black Page With Fading Color?

In some printers you get a good color with black print on the left side of the page which fades out to a monochrome only print on the right side of the page (or vice versa).


Being the good trouble-shooter that many of you are, you’re likely saying only one of the pair of alienation bars got stuck while the other one didn’t – and you would be right. If one gets stuck in the disengage position, one side of the image drum can be developed while the other side is not. In this case, the color alienation bar on the left side stuck causing just the color toners to not develop on the right side.


As it turns out there are a couple things to look for. Some of these are covered in an HP service note that came out late 2006, some are not. Here’s the quick run down:


SYMPTOM 1

Blank pages when printing in black and color pages have no black print. Do the common checks first

  • Verify the black toner cartridge is good

  • Look for objects in the black toner cartridge slot that may not allow it to fit fully into its slot

  • Are the black high voltage contacts clean and undamaged (power off printer and unplug before inspecting and cleaning)

  • Does the black shutter for the laser beam open and close properly (do not check this with the power on as this could expose you to the invisible laser beam and damage your eyes)

  • Inspect alienation bars behind the black toner cartridge to make sure they are not out of position. Run the Alienation Motor test and verify they move and are functional (see Alienation motor test below).

SYMPTOM 2

Black prints look good, but no color on color prints

  • Same steps as above with a focus on the color toner cartridges instead of black

  • Print a configuration page to isolate between printer driver issues vs. printer issue (e.g. verify the driver is not set to print monochrome only)

SYMPTOM 3

Black or all three colors fade out on the left or right side of the page

  • Here, we’re going to jump right into the inspection of the alienation bars behind the toner cartridges to make sure they are not out of position. Run the Alienation Motor test and verify they all move.

The Alienation Motor test cycles the engagement of both the color and black toner

cartridge alienation bars. To run this test:

  • Remove all the toner cartridges. Using a non-conductive object, engage the front cover interlock on the printer (center right of the printer as you face it)

  • Turn on the power

  • Find the diagnostics menu in the standard menu options. Choose Component Test, and then Alienation Motor test.

  • You will be able to watch the alienation bars lift and drop for both black and color. You’ll also notice the cams on the silver rod that drives them. Make sure they are clean and functional.

ALIENATION MOTOR TEST


If an alienation bar does not move and appears to be stuck, turn the power off and unplug the printer. It is better safe than sorry. Try to pop the alienation bar back into position once the power is off. Be careful to not break the bar.


This is a little tricky so if you do break it, rest assured that there are printer parts available. HP introduced a kit which contains the alienation bars, should one or all become damaged. The part number is Q3668-67925, Cartridge Alienation Plate Kit and available.


One More Possibility

If the alienation bars are not moving at all or not as far as they should, it could be a problem with the assembly that drives the alienation bars.


On the left side of the printer behind the covers, there is something called the alienation rod. This rod moves up and down and engages the toner cartridges as they need to be used for imaging and cleaning. In some instances, toner, dust and other “gunk” build up on the teeth of the alienation rod which keeps it from fully moving the cams.


Thus not fully moving the alienation bars creating our image creation issues. You may have to get your toner vacuum in there to clean out the teeth of this bar so it can move easier. We’ve heard from customers who have come across this issue so don’t assume it’s OK.


If you need to take apart some of the components to clean them, you’ll want to have your service manual available as the alienation rod has a specific reinstallation procedure and is not something you want to guess at.


Be careful as this is a live test that is performed with the doors open! Do not touch things in the printer as there are live voltages, and high voltages inside.


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