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These cartridges are basically a rectangular shaped cartridge that comes with a toner seal and a snap-on drum cover across the bottom to protect the drum. See Figure 1. These printers also have a separate waste bottle to collect the waste toner from the ITB belt.

These cartridges use chips that need to be replaced each cycle.

The printers based on the CP4520 engine are the:
HP Color LaserJet CP 4025n
HP Color LaserJet CP 4025dn
HP Color LaserJet CP 4525n
HP Color LaserJet CP 4525dn
HP Color LaserJet CP 4525xh

The cartridges used in these machines are the:
CE260A (Black) 8,500 pages $220.48 List*
CE260X (Black HY) 17,000pages $348.74 List* (4525 models only)
CE261A (Cyan) 11,000 pages $399.62 List*
CE263A (Magenta) 11,000 pages $399.62 List*
CE262A (Yellow) 11,000 pages $399.62 List*
CE265A (Toner collection unit) $18.00 List*
* Pricing current as of March 2010.

HP-CP4520 Color Printing Theory

The color toner cartridge printing process happens in a series of stages or steps. For the purpose of this article, we will call them stages. Figure 2 shows the basic layout of the cartridges and how they relate to one another and the printer. Note that while this is still a single pass system, the layout is completely different from any previous Canon/HP machines. The laser units are on the bottom, the cartridges are at an angle, and the ITB is on top. Figure 3 shows the complete image formation process.

In the first stage, light from the pre-exposure LED strikes the drum to remove any residual charges from the drums surface. See Figure 4. Then the primary charge roller (PCR) places a uniform negative DC voltage on the OPC drum surface. The amount of the negative DC voltage placed on the drum is controlled by the printer’s intensity setting. See Figure 5.

In the second stage, a dual laser beam is fired onto a rotating mirror (called the scann er). As the mirror rotates, the beams are reflected into a set of focusing lenses. The beams then strike the drum’s surface, reducing the negative charge and leaving a latent electrostatic image on the drum. The areas where the lasers did not strike the drum will retain the higher negative charge. While some previous printers had one scanner unit with four lasers, these machines have two separate laser/scanner units — one for black and cyan, and one for magenta and yellow. Dual lasers are used to allow faster print speeds. See Figures 6 and 7.

The third or developing stage is where the toner is developed on the drum by the developing section (or supply chamber), which contains the toner particles. The development stage is actually made up of two steps: toner charging and the actual development. In the toner charging stage, the toner stirring blade turns inside the hopper. As it turns, friction causes a negative potential to develop on the toner. In addition, a foam feed roller brings the toner to the developer roller and also places a negative charge on the toner. These two charges help ensure a uniform charge on the toner. Once the toner is properly charged, the toner will coat the developer roller. The toner is also held onto and attracted to the developer roller by another negative DC bias voltage. This voltage is controlled by the printer’s intensity setting and causes either more or less toner to be attracted by the developer roller. This in turn will either increase or decrease the print density. The amount of toner on the developer roller is controlled by the doctor blade, which uses pressure to keep the amount of toner on the roller constant.

As the laser exposed areas of the OPC drum approach the developer roller, the toner particles are attracted to the drum’s surface due to the opposite voltage potentials of the toner and laser exposed areas of the OPC drum. See Figure 8.

The fourth stage is the transfer stage. This is where there are some large differences from monochrome printers and also from other color lasers. In the primary transfer stage the transfer roller which is located directly opposite each OPC drum, places a positive DC bias charge on the back of the ITB or image transfer belt. Each toner cartridge has a separate transfer charge roller. The image is transferred from the drum directly to the ITB. This process is repeated for each color cartridge in the following order: yellow, magenta, cyan and black. At the same time, the paper is moving between the secondary transfer roller and the ITB. As the ITB passes the secondary transfer roller, the positive charge is picked up, and draws the negatively charged toner off the belt and onto the paper. Note that this entire process is upside down from most previous HP engines. The ITB and transfer rollers are on top of the OPC drum, not underneath it. See Figure 9.

The paper separates from the ITB belt as the belt turns back down to start the process again. The static charge on the back of the paper is decreased with static charge eliminator. This helps stabilize the paper feed, and also prevents toner flares (spots) under low temperature and low humidity conditions. See Figures 10 and 11.

In the fifth stage, the image is then fused onto the paper by the fuser assembly. The fuser assembly is comprised of the upper heating assembly and lower pressure roller. The lower pressure roller presses the page up into the upper heating assembly which then melts the toner into the paper. This heating assembly consists of a flexible sleeve with a ceramic heating coil inside. This type of fuser affords "instant on” fusing with little to no wait time, and low power consumption. See Figure 12.

ITB cleaning:

The ITB is cleaned by the ITB cleaning blade. The ITB wiper blade scrapes off the residual toner and an auger moves the toner to the toner collection box. See Figures 13 and 14.

OPC Drum Cleaning:

The drum is cleaned after the image is transferred to the paper by the wiper blade. This part is fairly standard; the wiper blade scrapes the toner off the drum, and the recovery blade guides it into the waste chamber. See Figure 15.

These printers can print in full color or in black only modes. To print in the black only mode, the printer disengages the developer rollers in the cyan, magenta, and yellow cartridges. This process also takes place with the primary transfer rollers and the ITB belt. See Figures 16 and 17.

Printer calibration:

At the start of all this is the cartridge detection process, toner level detection, and then the calibration cycle. The printer will calibrate itself whenever the printer is turned on (within 15 minutes), when a new toner cartridge is installed and after 48 hours of run time. Calibration consists of a solid block and halftone of each color being printed to the ITB. As the printed areas get to the top of the belt, a sensor will detect them, measure the density, and adjust the printer accordingly. See Figure 18. All of the calibration time settings are user controllable.

Taking test prints, cartridge troubleshooting as well as minor printer troubleshooting will be covered at the end of this article.

Required Tools

1. Toner approved vacuum
2. A small common screwdriver
3. A Phillips head screwdriver
4. Needle nose pliers

Required Supplies

1. CP4520 Dedicated Color Toner
2. New replacement chip
3. New Long Life CP4520 Drum
4. New wiper blade
5. New toner feed roller [optional]
6. New PCR [optional]
7. New doctor blade [optional]
8. Drum cover
9. Lint free cloths
10. Conductive grease

The pins in these cartridges are stepped. In other words the outside is thicker than the inside. To remove the pins, you must carefully shave the plastic away from the pins. The procedure is described below.

1) Remove the spring from the label side of the cartridge. See Figure 19.

2) With a razor knife, carefully shave the plastic from the heads of the hinge pins on both sides of the cartridge. See Figures 20, 21, 22 and 23.

3) On the label side only, drill a shallow hole on each side of the pin as shown in Figures 24 and 25.

4) Remove the pins with flush cutting wire cutters. The smaller pin fits on the contact side of the cartridge, the long pin on the label or gear side. See Figures 26 and 27.

5) On the gear side, press in on the plastic locking mechanism. See Figure 28.

6) On the opposite side lift up on the black lever. Lift the two halves apart. See Figure 29.

7) On the waste chamber, remove the two screws from the drum gear end cap. Press in on the tab as shown and remove the end cap. There is no need to remove the opposite side end cap. See Figures 30 and 31.

8) Remove the drum. See Figure 32.

9) Remove the PCR by lifting up on the black and white PCR locking arms. Remove the PCR assembly. See Figure 33.

11) Remove the two screws from the wiper blade. Slide the razor knife along the back edge of the blade to release it from the glue. Remove the wiper blade. See Figures 36, 37 and 38.

12) Clean out all the waste toner from the chamber. Try not to get any toner on the WB seal if possible.

13) Clean the felt seals on each end of the wiper blade. If the WB glue has toner on it, clean it off with alcohol and a foam swab. If it does not become sticky again, it needs to be removed and a good silicone caulk used to seal the blade off. GE 100% Silicone and Phenoseal are two good brands for this purpose. See Figures 39 and 40.

14) Install the new wiper blade and two screws. If you removed the WB glue, seal the back edge of the blade with the silicone now. See Figure 41 and 42.

15) The amber film assembly is held in place with double sided tape. If this is not sticking or a new wiper blade is being used, replace the tape. Replace the film assembly. See Figure 43.

16) Clean the PCR with your preferred cleaner and install in the cartridge with the PCR holders. Make sure you lock the locking arms in place. See Figures 44 and 45.

17) Install the drum. Short hub side onto the long drum ground pin. See Figure 46.

18) Install the end cap and two screws. See Figure 47.

19) Place the waste chamber aside.

20) On the supply chamber, remove the screw from the gear side end cap. See Figure 48.

21) Press in on the tab and remove the end cap. See Figure 49.

22) On the center gear, press on the locking tab to release the gear. Remove all the gears as shown except for the mixing blade gear and the sealing strip gear. The mixing blade gear is attached to the mixing blade inside the hopper and is very difficult to re-attach properly. See Figure 50.

23) On the contact side, remove the two screws, press in on the tab and remove the end cap. See Figures 51 and 52.

24) Remove the three developer roller drive gears. See Figures 53 and 54.

25) On the gear side inner end cap, remove the two screws and end cap. See Figure 55.

26) Remove the developer roller. See Figure 56.

27) Remove single screw and contact side inner end cap. See Figure 57.

28) Remove the two screws from the doctor blade and start to lift the blade up. There is glue on either end of the blade. As you lift the blade up, slice the glue away from the blade with the razor knife. See Figures 58, 59 and 60.

29) On the right side of the chamber lift up the felt developer roller seal. Lift it from the front side and lay it over the back. See Figure 61.

30) Remove the white felt washers from both sides of the feed roller. See Figure 62.

31) Pry out the rubber feed roller bushing from the right side. See Figure 63.

32) Remove the feed roller. See Figure 64.

33) Clean out the remaining toner and fill with the correct color of dedicated CP4520 toner. See Figure 65.

34) When a seal is available, install the seal onto the seal rails. Pull the release tape off one inch at a time and press the seal in place as you go. See Figure 66.

35) Remove the seal port and slide the seal pull tab through the slot. Install the seal port. See Figures 67 and 68.

36) Install the feed roller and rubber bushing. See Figure 69.

37) Install the feed roller felt washers. See Figure 70.

38) Press the developer roller felt seal back in place. Make sure it fits under the retaining blade. If needed, clean the adhesive with alcohol and a foam swab. See Figures 71 and 72.

39) Use the appropriate shims to gap the blade and install the doctor blade and two screws. Make sure the sticky seals on either end of the blade seal correctly. If the material is no longer sticky clean it with alcohol or replace it with a small amount of silicon. See Figure 73.

40) Clean the contacts and replace the conductive grease on the inner contact end cap. Install the inner contact end cap and screw. See Figure 74.

41) Install the cleaned developer roller. (Do not use any chemicals to clean this. A lint free cloth works fine.) See Figure 75.

42) Install the inner gear end cap and two screws. See Figure 76.

43) Install the gears in the order shown. If you installed a seal, slide the seal end through the take up gear and wrap the loose tail tight on the roller. See Figure 77.

44) Install the remaining gears in the order shown. See Figure 78.

45) Install the outer gear end cap and screw. See Figure 79.

46) Place the triple gear on the developer roller shaft and fit into the spring assembly on the end cap. Install the opposite side end cap and install the screw. See Figures 80, 81 and 82.

47) Place the two halves together contact side first. On the gear side, press the lever in place. On the contact side snap the lock up into the end cap. See Figures 83 and 84.

48) Install the two pins. Large pin to the label or gear side of the cartridge. See Figure 85.

49) Install the spring. See Figure 86.

50) Remove the chip by cutting the plastic off the edges of both sides of the chip. See Figure 87.

51) Remove and replace the chip. See Figure 88.

52) If the new replacement chip is loose in the slot, close off the top edges with small amounts of hot glue.

53) Install the drum cover on to the cartridge. See Figure 89.

Taking Test Prints

Configuration page:
Press the Home button
Press the down arrow until INFORMATION appears on the display
Press OK
Press the down arrow until PRINT CONFIGURATION appears on the display
Press OK

Color band test pages:
Press the Home button
Press the down arrow until DIAGNOSTICS appears on the display
Press OK
Press the down arrow until COLOR BAND TEST appears on the display
Press OK
Press the down arrow until PRINT TEST PAGE appears on the display
Press OK
A page of color bands pages will print out allowing you to see that all cartridges are printing correctly