Recharger Magazine

The leading information resource for the document printing industry aftermarket.

HP 4500 Drum Kit and Toner Cartridge Disassembly

Nov 01, 1999

Released in October 1998, the Hewlett-Packard Color LaserJet 4500 is currently leading the pack in color laser shipments in both the U.S. and world markets. Recent projections reflect that more than 200,000 of these printers will be sold in the United States by the end of the year 2000. With this in mind, the HP 4500 likely will be one of the most important new color laser engines for the remanufacturing industry during the next several years.

Continuing the exclusive partnership between HP and Canon, the HP 4500 is based on Canon's new EP-83 engine. The EP-83 is the first color laser engine to eliminate the need to oil the fuser. Canon's color toner formulation is the main contributor to this milestone. The color toners are manufactured using a chemical process to produce uniform, spherical particles with a microscopic bead of wax at the core of each particle. As a result, the toner blends smoothly during fusing without the aid of oil. This progressive design will present development challenges to competing OEMs as well as aftermarket developers.

The supplies set for the HP 4500 consists of seven consumables:

OPC drum kit
four color toner cartridges (cyan, magenta, yellow and black)
fuser kit
transfer kit.

The OPC drum kit and four color toner cartridges are the five core replacement items. The black toner is magnetic and manufactured through a conventional milling process, which is familiar technology to the remanufacturing industry. All seven consumables are designed for replacement by the enduser. Aftermarket supplies opportunities for the HP 4500 will most likely begin with remanufacturing the drum unit, then the black toner cartridge, followed by the color toner cartridges. As the market matures, remanufactured transfer and fuser kits will probably emerge.

For more information regarding the market background, supplies and imaging process of the HP 4500 printer, refer to "Color LaserJet 4500: Seizing the Top Color Market Position" in the July 1999 issue of RECHARGER Magazine.

About the OPC Drum Kit

The OPC drum, wiper blade and PCR are housed in the OPC Drum Kit. The unit also contains a reservoir to collect waste toner from the drum and intermediate transfer belt. An electronic memory chip can be found on the side of the drum kit. The chip's function is to collect and store information to estimate the end of the drum life in order to maintain good print quality. According to Canon's patent information, the chip records the amount of drum revolutions, the accumulated time the drum has been charged by the PCR, and the amount of toner in the waste bin. When the estimated end of drum life is reached, the chip shuts down the unit to prevent a decline in print quality. The user is also alerted to replace the drum unit. Successful remanufacturing of the drum unit requires either resetting the memory chip or replacing it.

About the HP 4500

Toner Cartridges

A series of electrical contacts and electronic components in both the black and color cartridge are located in the end plates near the doctor blade. These serve to help control toner migration by maintaining specific voltages for the developer roller and doctor blade.

The electrical contact pin on all the cartridges serves as the contact for the end plate and the pivot point for the shutter. Because of this dual function, it is especially important to exercise care when removing the electrical contact pin during disassembly. The locking tab on the contact pin is easily worn and may not function properly after several disassemblies if it is not properly released during removal of the contact pin.

The hoppers for both the black and color cartridges can be split and sealed. The hopper cap is located beneath the mag roller end plate and can be accessed for filling toner whether or not the hopper is split.

The black toner is magnetic and manufactured through a conventional milling process. The color toners are chemically manufactured to achieve a more uniform shape, composition and size. Development in the black cartridge is achieved through a magnetic process, whereas the color cartridges use an electrostatic development process. The internal design and components between the black and color cartridges for the HP 4500 vary slightly due to this difference in process. As a result of design differences, the disassembly instructions for the black and color cartridges are not completely the same.

The most notable component difference between the black and color cartridges is the doctor blade configuration. The black cartridge has a silicone blade attached to a typical metal stamping and has the same dimensions as the HP 4000 doctor blade. The configuration of the doctor blade in the color cartridges resembles that of the Lexmark Optra C, a urethane material attached to a thin, flexible copper-alloy blade. The color cartridges also incorporate an additional roller assembly attached to the doctor blade that is not present in the black toner cartridge. The roller assembly must be removed to get to the doctor blade. The extremely small screws that secure the assembly are easily lost and require a jeweler's screwdriver or other small tool for removal.

As an external design note, all the color cartridges have a removable tab for cartridge identification by the printer. Each color has a specific position. Although the cartridges are interchangeable by repositioning the tab, it is not recommended to do so. First, even an extremely thorough cleaning of the cartridge would not completely prevent cross-contamination of the color toners. Second, the cartridge would need to be relabeled with the proper color label.

Click to view enlarged photo.

OPC Drum Unit Disassembly

1. Remove the drum shutter actuator screw.

2. Remove the drum shutter.

3. Remove the screws from the end plate (electronic chip side).

4. Remove the screws from the drive coupler end plate.

5. Remove the drive coupler end plate.

6. Remove the bearing

7. Remove the end plate (electronic chip side).

8. Remove the OPC drum.

9. Remove the PCR cover.

10. Remove the PCR.

11. Remove the wiper blade screws.

12. Remove the wiper blade.

13. Remove the electronic chip assembly.

14. Pull out the electronic chip assembly.

15. Remove the five agitator axles. Not the notch in the lower axle (above) and the square hole in the upper axle(below). The other three axles are identical.

16a. Remove the agitator dirve gears as illustrated in 16a-16e.

16b.

16c.

16d.

16e.

Black Toner Cartridge Disassembly

NOTE: For disassembly of the Color Toner Cartridges, after completing steps 1-9, go to the Color Toner Cartridge Dissassembly Instructions.

1. Remove electrical contact pin. Insert a small flathead screwdriver to release the locking tab and simultaneously pry up to remove the electrical contact pin (above). A close-up view of the contact pin is shown below.

2. Release the shutter latch with a small flathead screwdriver.

3. Pull the shutter over the drive end plate.

4. Remove the screws from the seal exit end plate.

5. Remove the seal exit end plate.

6. Remove the screws from the drive gear end plate.

7. Remove the drive gear end plate.

8. Remove the electrical contact and drive gear from the mage roller.

9. Remove the main drive gear from the cartridge.

10. Remove the agitator drive gear.

11. Remove the mag roller and mag roller bushings.

12. Remove the doctor blade tabs by removing screws.

13. Remove the doctor blade screws.

14. Remove the doctor blade.

Color Toner Cartridge Disassembly

NOTE: For disassembly of the Color Toner Cartridges, first follow steps 1-9 of the Black Toner Cartridge Disassembly Instructions, and then proceed with the following steps.