How the Black Print Cartridge Drops into the Developing Position

After the black print cartridge is installed in the printer, the black cartridge lever assembly is lowered. This moves the black print cartridge into the developing position. With all HP Color LaserJet 8500 models and some 8550 and 8550 MFP models, a gear assembly dampens this movement.

After the black print cartridge has been inserted into the printer it is locked into position by lowering the blue cartridge lock lever back into the vertical position. This locking action activates the black print cartridge switch (SW644). When activated this tells the printer the black print cartridge is installed and locked into place. If the printer is not recognizing the black print cartridge properly, this switch is the most likely cause. The switch is accessible after removing the back cover. See Figure 1, the circled area shows the switch properly activated. The small rod moves to the bottom of the slot when the lock lever is put into the locked position. It also activates the small red micro switch in the circled area.

Figure 1: Black print cartridge detection switch (SW644)

In the HP Color LaserJet 8550 models outlined in the table below this dampening assembly has been eliminated. The black cartridge will drop into the developing position quicker when the blue lever is locked on these models.

The gear assembly is shown in Figure 3.

HP Color LaserJet 8550 and 8550 MFP models that do not have the dampener assembly

Accessing the dampener assembly

If the black print cartridge appears dropping into place too quickly when the blue lever is locked and the printer is NOT within the serial number range that does not have the dampener then the assembly should be visually inspected. To do this several parts need to be removed.

Open the front door and remove the right-front cover (one screw).

Open the right door and the left-upper cover assembly, then loosen the four screws that hold the top cover in place (two on each side).

Gently lift the top cover off of the printer a couple of inches and disconnect the cable that goes to the control panel.

The black plastic airflow vent by the delivery assembly must be popped off. See Figure 2, call-out 1.

Figure 2: Airflow vent 1-Pop this airflow vent off to see the dampener assembly

Figure 3: Black print cartridge dampener assembly 1-Close-up of gear assembly

Verifying functionality

Insert a black print cartridge.

Lock the blue lever while watching the dampener gears. The black gear should be turning as the white piece moves up and down. The white piece is attached to the sheet metal assembly in which the black cartridge sits. See Figure 3, call-out 1.

If this assembly is missing or not working correctly inspect the printer for the missing components. The dampening assembly is held in place by one screw. If any damage is found remove the dampening assembly.

© 2005 Hewlett-Packard