The HP color laserjet 4600 series machines are a perfect example of why HP has become legendary for their line of laser printers. In today’s market, while this is not one of the quicker machines out there, its high volume print cartridges, durability, and ability to handle any job an end-user can think of makes this printer series an office favorite. However, with its age the laser scanner optics are getting a build up of dust and debris on the mirrors and lens. While the light and faded print doesn’t happen as quickly and is not as apparent on this model as it is in the HP color laserjet 2600 and 3000 series, it still needs to be addressed.
In this article I will discuss what you can expect when light or faded print starts becoming an issue in the HP color laserjet 4600 series, how to troubleshoot the problem, and how to resolve the light or faded print issue when it has to be fixed.
Reported Problem from the Customer
Most of the service requests I get on this machine are due to light or faded print on the left side of the printed page, either in one color or all colors. Sometimes when customers have a very bad toner spill they blow it out and toner will get stuck on the main mirror resulting in a faded vertical line running down the page in random areas. Or in extremely dirty environments the whole image gets light.
What Causes the Problem?
Unlike new color laserjet models, the 4600 series color laserjets still use four laser scanner units to produce the four colors. Because these machines have laser scanner units like the monochrome series, the units are better sealed and the optics are kept level so dirt and debris doesn’t build up on them like newer models. Most of the time the dust and debris build up happens on the polygon mirrors located atop the laser motor. The polygon mirrors rotate like a fan. If you’ve ever cleaned a fan off you’ve probably noticed the dust builds up on one side. Same goes for the mirrors in the 4600 laser units. As they rotate dust tends to build up on the left side of the mirrors. Once this starts to happen the left side of the image becomes faded.
Troubleshooting Light or Faded Print in the HP Color Laserjet 4600 Series Printer
The first step in troubleshooting print quality problems is to print a demo and configuration page from the information menu and/or the PQ troubleshooting pages from the diagnostics menu. The demo page mainly helps to see how colors are being mixed together. The configuration page is good at showing faded print across the four color planes. The four lines at the bottom should have uniform color fill throughout the bars. Each of the bars represents that toner cartridge as the bar produced is strictly just using that color toner cartridge to produce the bar. If the optics are dirty the color will be generally faded on the left side but can be faded in other spots if dirt or dust has build up on the front optics of the laser scanner unit. The PQ troubleshooting pages will also help with faded print issues as they print full pages of the individual colors.
For some reason the 4600 series printers don’t always do a good calibration when toner cartridges are installed. I’ve serviced a number of machines where the image color on the demo page was so far off! After doing a color calibration the image quality was restored and I could go about fixing other issues.
After you have printed test pages go into the config device menu, scroll and click on the print quality submenu. On the 4600 run the ‘calibration now’ and on the 4610 and 4650 run the ‘full calibration’. After the calibrations have finished go back and print the test pages again to see if you notice any difference. If your problem’s been fixed, great! If not, read on.
So, Your Problem’s Not Fixed!
If you still have faded or light print after the color calibration we need to further troubleshoot. If all the colors are faded on the left side then you probably can move on to the disassembly instructions. If you just have an issue with one or two colors then we can troubleshoot more.
For example if only the magenta bar has faded print on the configuration page we can troubleshoot the cartridge and the laser scanner unit to isolate the problem. By following the procedure below we can put the machine into diagnostic mode and disable the cartridge check.
Diagnostic – Disable Cartridge Mode
1. Press the Check button (HP Color LaserJet 4600 models) or MENU (HP Color LaserJet 4610n and 4650 models) to open the MENUS
2. Press to highlight DIAGNOSTICS
3. Press to select DIAGNOSTICS
4. Press to highlight DISABLE CARTRIDGE CHECK
5. Press to select DISABLE CARTRIDGE CHECK
Once the cartridge check is disabled we can swap the magenta cartridge with the black cartridge or cyan cartridge (I would avoid swapping the yellow cartridge because it can be hard to tell if it actually faded or not), and reprint the configuration page. If the faded print color on the left side stays with the magenta color we know the magenta cartridge is causing the problem. If the faded print changes from the magenta color bar to whatever color you swapped it with then we know the optics in the laser unit are in need of cleaning.
Cleaning the Laser Scanner Assemblies
This is a very intensive procedure. If you haven’t performed a major repair on a printer I would not recommend trying this. It takes a lot of work to remove the units and they have to be positioned just right when reinstalling them. If you fail to do it just right you will be performing this procedure all over. I usually install the laser units back in and run the print test with the covers off to avoid completely doing the removal again if the laser units aren’t positioned correctly.
Let me say that again! If you haven’t done major printer repairs, this is not the repair to start with. Call your service company. You’ll be glad you did.
Removal of the Laser Scanner Assemblies
1. Remove two screws, top below vents.
2. Pull out on the left side of the rear cover, and slide it to the left to remove it.
Fuser Unit Removal
1. Turn the printer off.
2. Use the side handles to open the top cover.
3. Completely loosen the blue thumb screws on each side of the fuser.
1. Using your fingers or needle-nose pliers, pinch and release the white plastic clips on the damper arm on the left side of the cover. It is easier to pinch these clips if you tip the top cover forward slightly.
2. Disengage the tab and remove the retaining block.
3. Push the cover to the left to release the hinge pin on the right side, then pull the cover to the right to release the hinge pin on the left side and remove the cover.
Rear top cover
1. Remove three screws, top by fuser area.
2. Insert a flat-blade screwdriver between the rear top cover and side cover on the right side of the printer.
3. Lift the screwdriver slightly to disengage the tabs on the right side of the printer.
4. Repeat steps 2 and 3 for the left side tabs on the left side of the top rear cover.
5. Remove the rear top cover.
DC controller shield
1. Remove nine screws. A tenth screw might be located on the rear of the printer at the bottom of the DC controller shield. If that tenth screw is present, remove it.
2. Remove the DC controller shield.
1. At the rear of the printer, remove eight screws.
2. On the DC controller PCA, release the brown tab covering the formatter ribbon cable and disconnect the cable.
3. Disconnect one connector and remove the formatter case.
1. On the DC controller PCA, disconnect four connectors.
2. On the DC controller PCA, release the brown tab covering the formatter ribbon cable and disconnect the cable.
3. At the rear of the printer, place the cardboard spacer (included with the laser/scanner assembly) underneath the V mark on the bottom of the chassis.
4. Remove four screws.
5. Using needle-nose pliers, pull down on the right side of the wire clip, then release the left side of the clip from the bracket. Repeat this step for each of the four clips.
6. Remove the plate that covers the laser/scanner units.
Remove the laser/scanner retaining bars
1. Remove the laser/scanner cover plate.
2. Pull the cables for the four laser/scanner connectors free of the printer chassis.
3. On the left side of the printer, remove one screw above the DC controller.
4. Push the top of the sheet-metal scanner retaining bar towards the laser/scanner units.
5. Rotate the bar down and carefully remove it from the printer.
6. On the top surface of the right side of the printer, remove one screw.
7. On the right side of the printer, push the top of the sheet-metal scanner retaining bar in towards the laser/scanners.
8. Rotate the bar down and carefully remove it from the printer.
To remove the laser/scanner assemblies
1. Remove the laser/scanner retaining bars (as described above)
2. Slide the cyan laser/scanner unit to the left and then pull it out of the printer.
3. For the yellow, magenta, and black laser/scanner units, first unhook each assembly from the white strap, then pull the laser/scanner units out of the printer.
CAUTION: When reinstalling the laser/scanner units, always reconnect them to the white strap behind where the scanners sit. Failure to do so could cause the laser/scanners to become distorted, and the laser beam could become skewed, resulting in image defects.
Also when reinstalling the laser unit move it around a little when you get it in. There are posts in the front of the laser scanner unit that need to align with the front of the frame. If you fail to do this after you reinstall the unit your colors could be shifted vertically, resulting in another disassembly. As I stated before, I usually don’t fully reassemble the machine until after I have run some print quality test.
Cleaning the Laser Scanner Optics
Once you have the laser unit out remove the screw or screws on the top metal plate and check out the polygon motor mirrors in back of the unit on top of the laser scanner motor PCA.
If there is a build-up of dust on the mirrors you should notice it. Take a Q-tip and gently brush off the mirrors.
The mirrors can easily be damaged. I prefer to brush it off gently several times rather than once using more pressure. I recommend using one Q-tip side for each mirror to avoid dirt from the previous mirror scratching the next mirror.
As I tell everybody, at this point it is not a race. Take your time and do it right the first time. Take the laser unit and move it around at different angles so you can look at it from different points of view and make sure you have all the dirt and debris off the mirrors. The laser units are all the same; so if you’re really in doubt that cleaning the laser scanner will solve the problem you can always switch a laser unit with another and test it in another slot to see if the issue follows the laser unit to another color.
Additionally, since you have all the laser scanners right in front of you I would take the covers off all of them and clean them and/or check to make sure there is no dust and debris build up on the other ones, as well.
Conclusion about the Light or Faded Print in the HP Color Laserjet 4600, 4610, and 4650
If you had to perform the laser scanner cleaning procedure I hope that by following the instructions above you have fixed your light or faded color problems and have gotten your machine back up and running with the print quality restored.
Kevin Gumpp is a certified printer technician and freelance writer for Market Point. HP Diagrams are from the HP Service Manual for the 4600 CLJ. Additional photos courtesy of Bill Raymond, a certified printer technician at Market Point. If you have a question regarding this topic or have any other printer repair related questions or topics for which you would like more information, please send an email to firstname.lastname@example.org.