This article shows how to clean the Scanner on the Hewlett Packard 4000 series Laser Printers.
This service procedure needs to be done when the machine is in a dirty environment and the dust builds up on the mirror inside the scanner.
Symptoms of a dirty scanner:
Light prints even after you have tried a new toner cartridge. Mostly shows itself as light prints on one side of prints or streaks or wide blank lines. HP LJ-4250: Blank streak down the middle of page. Note:This procedure is basically the same for the Following LaserJet Models: 4000, 4050, 4100, 4200, 4300, 4250, 4350, P4015, P4515
Getting to the Scanner:Turn the power off and remove the power cord. Remove the right rear side cover. Push the cover toward the rear and it will slide out. Open the top cover and remove the toner cartridge. Remove the toner cartridge drive arm. Remove the Toner Cartridge Drive Arm by using needle-nose pliers to pinch the pin from its hinge on the Top Cover. 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). 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. Holding the output assembly in place (located toward the rear of the printer), remove the Top Cover. Disconnect the wiring connector(s).
Remove output assembly:
Facing the rear, pull up brass arm on the left side straight up. Pry the white tab on the right side and pull the output assembly up and out. Caution: Be careful of the sensor flag. When reinstalling make sure it rotates freely.
Removing the Scanner Cover:
Carefully remove the wiring connectors. Remove the cover of the scanner by removing the screws and using a small flat blade screwdriver to release the latches. Carefully remove the cover.
Cleaning the Mirror:
The only mirror you will be cleaning is the one that shines directly on to the drum in the toner cartridge. This mirror is at an angle. You need to clean the mirror from below. Use a Q-tip to clean it. Make sure you clean the edges really good. Reinstall everything in reverse order.