Light Print -Laser  Scanner Repair –  HP Laserjet 4000, 4050, 4100
Light print on the HP laserjet  4000, 4050, and 4100 printer models is becoming a more common problem as these machines age. The light print problem can be throughout the whole page or more commonly on the left side. The problem is usually a result of dust build up  inside the laser unit on the polygon motor mirrors. The motor has several mirrors on top of  it that rotate at around 10,000 to 20,000 RPM’s depending on the machine. Like a ceiling fan in your house the outer edges of the mirrors, as they rotate, tend to attract more debris and dust. As this dust builds up on the mirrors the laser image doesn’t write as clear to that part of the drum. The result is faded print on your paper. Like a mirror in a bathroom. After you take a shower you can’t see clearly  in the mirror, Once you take a towel and clean it off your back in business. Same goes for light print on the HP laserjet 4000, 4050, and 4100 printer. If you clean the mirrors off inside the laser unit  you can restore the print quality and remove your light print.
Troubleshooting light print in a HP Laserjet 4000, 4050, 4100 Printer
I added more detail to the troubleshooting tips. Instead of making this article extremely long I decided to create a new article and link to it. Below is the updated article for further assistance on your light print issues.
Troubleshooting Light or Faded Print – HP Laserjet Printers
Laser Scanner Cleaning Procedure for Light Print on a HP Laserjet 4000, 4050, 4100 Printer
Removal: Formatter Cover
1. Grasp the cover by its rear lip and pull it firmly toward the rear of the printer until it stops.
2. Remove the cover from the printer
Top Cover
1. Â Remove the four screws holding the Top Cover (two are behind the Rear Output Bin, near the top, and two are on top of the printer under the Top Cover).
2. Â Open toner cartridge door. Remove the Toner Cartridge Drive Arm by using needle-nose pliers to pinch the pin from its hinge on the Top Cover.
3. Â Squeeze the right front side of the Top Cover to remove it. It may be necessary to use a small flat-blade screwdriver to release the tab inside the small hole.
4. Holding the output assembly in place (located toward the rear of the printer), lift  the Top Cover up slightly.
5. Tilt the left side up and locate the control panel cable underneath the control panel and disconnect. Now you can completely remove the top cover.
Output Bin
1. On the left end of the assembly, rotate the brass arm up 90
2. On the right end of the assembly, release the white tab.
Laser Scanner Cover. Large Black Piece with Yellow Warning label on Top
1. Â Disconnect two cables on top the unit and remove two small black screws
2. Release four tabs. Two in back and two in the front on the side.
3. Lift and remove cover.
Cleaning the Laser Scanner Unit
If the laser scanner is relatively clean inside then I would just clean the front mirror  shown in the picture below and the motor mirrors located in the bottom of the unit on top the motor. Use a  Q-tip to clean the mirrors. If you see any build up on the Q-tip get a new one before proceeding to the next mirror. The most important thing here is to take your time and be gentle. The motor mirrors are metal and extremely delicate. They are very easy to scratch. You should notice before you clean the units a build up of dust and debris on the mirrors. Especially on the left side of the motor mirrors. If the unit is very dirty inside then I would clean all the mirrors and lens inside the unit and blow it out before I put it back together.
Conclusion about Light Print in the HP Laserjet 4000, 4050, and 4100 Printer Repair
The light print problem in the HP laserjet  4000, 4050, and 4100 is becoming a more common issue as these machines age. Hopefully the article above will help you troubleshoot and diagnose your problem so you can resolve your light print issue in your HP laserjet 4000, 4050, and 4100 printer and get your machine up and running without any further print quality problems.
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