Recharger Magazine

Remanufacturing the Xerox Phaser 7400

• By Mike Josiah
• Sep 01, 2007

The Xerox Phaser 7400 printers are based on a 36-ppm color/40-ppm monochrome, 1,200-dpi engine. All versions are based on an 800 MHz PowerPC chip, and come standard with either 256MB or 512MB memory (depending on the model). In all models the maximum is 1GB of memory. This engine uses a two-cartridge system, a toner tube and a drum unit. The toner tube is very easy to remanufacture, the drum unit is a bit more complicated but also fairly easy to do. Both cartridges will be covered in these instructions.

These units have four toner tubes, four drum units, a separate waste toner cartridge, and transfer unit. With the exception of the black, the toner tubes come in both standard and high-yield (9,000 and 18,000) models. The black tube comes only in a 15,000-page yield. It is interesting to note that both the toner tube and the drum unit need to be reset. The toner tube uses a chip while the drum unit uses a fuse. Both need to be replaced each cycle. The toner tube chips are hidden under the cartridge identification label, while the drum unit’s fuse is in an end cap.

In addition to the drum unit, the fuser assembly and transfer belts both have a fuse installed on them. When a new unit (drum transfer or fuser) is detected, the printer resets that unit’s life counter and then blows the fuse. The counter will not show as reset until two pages have been printed. After the counter has been reset, it will count the pages printed until the maximum life has been reached for that unit.

It is also important to note that new OEM drum cartridges come filled with toner. When you rebuild a drum unit, it is important to include a rebuilt toner tube so that the customer gets the same value. It is possible to fill the drum unit without a tube, but it is extremely difficult, and the possibility of dumping the toner is very high. A filled tube is a much better way to go, plus if you give them a high-yield version, you can charge more and still give your customers better value.

Figures A and B show how the drum unit comes packaged.

Figures C and D show the tab system that keeps different color toner cartridges from accidentally being installed in the wrong drum units. The cartridges shown are for the black system.

Since this printing system is different from anything covered in the past, we will be covering the printer theory here. Cartridge and printer troubleshooting as well as how to print test pages will be covered at the end of this article.

Cartridge theory

As with most other theory sections we have done, the easiest way to follow the theory is to break it down into a series of steps or stages. But first, the first three diagrams show, in general, the physical layouts of some of the more important parts.

Figure 1 gives an overview of the printer, the toner and drum (imaging) units as they all relate to each other. Note that these machines are not laser printers. They are LED printers. Each color has a bank of LEDs that writes the image to the drum.

Figure 2 gives a nice side-view breakdown of both the drum unit and the toner tube.

Figure 3 shows the LED heads in the top cover of the printer and their covers.

In the first stage, the Primary Charge Roller (PCR) places a uniform negative DC voltage on the OPC drum surface. The amount of negative DC voltage placed on the drum is controlled by the printer’s intensity setting. See Figure 4. This process occurs simultaneously for all four of the color cartridges.

In the second stage, the LED head emits light directly to the negatively charged surface of the drum. LED printers do not use scanners or mirrors; the LED head spans the width of the entire page with hundreds of individual LED lamps. This light leaves a latent electrostatic image on the drum. The areas where the light did not strike the drum will retain the higher negative charge. Unlike lasers, LED heads also have the ability to change the power of the light that strikes the OPC drum. This process allows for better control of halftones. Each color cartridge has its own LED head. All four LED heads operate simultaneously. See Figure 4 again.

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 feed (sponge) roller turns inside the hopper. As the sponge feed roller brings the toner to the developer roller it also places a negative charge on the toner. This charge ensures 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 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 light-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 LED light-exposed areas of the OPC drum. See Figure 5.

The fourth stage is the transfer stage. In this stage, the transfer roller (which is located directly opposite each OPC drum) places a positive DC bias charge on the back of the transfer belt. Each toner cartridge has a separate transfer roller that is made from a conductive sponge material. At the same time, the paper is moving between the OPC drum and the transfer belt. As the paper/belt passes the transfer roller, the positive charge is picked up and draws the negatively charged toner off the drum onto the paper. This process is repeated for each color cartridge. As the toner piles onto the paper, the positive charge on the paper weakens as the paper runs through each cartridge. For this reason, the charge is increased slightly from the transfer-charging roller for each successive color. See Figure 6.

In the fifth stage, the image is then fused onto the paper by the fuser assembly. The fuser assembly is comprised of the heating assembly and pressure roller. The pressure roller presses the page up into the heating assembly, which then melts the toner into the paper. The heating assembly consists of a flexible sleeve with the pressure roller inside and a heat roller that sits on top of it. This system is very different from other HP or Lexmark systems. See Figure 7.

Drum and transfer belt cleaning

The drum and transfer belt are both cleaned after the image is transferred to the paper. Unlike most of the more complicated HP systems, these machines have just a simple wiper blade/auger system that removes the old toner and places it into the waste cartridge. Both the drum unit and the transfer belt have separate cleaning systems, but all the waste toner from both units goes to the same separate waste unit. See Figure 8.

Toner-level detection

Each drum unit contains an agitation gear and agitation bar. The agitation bar moves the toner to the area above the developer roller. Located at the end of the agitator bar is the toner-low sensor target. Located in the printer, the toner-low sensor is an optical sensor that monitors the amount of light reflected back from the target. As the toner level drops, the period of time that the agitation bar remains at its highest point is reduced. This time change signals toner-level changes. There are three levels of toner status: OK, low and empty. When the empty state has been reached, the printer terminates the current job (at the end of the current page), and will
not accept any new jobs. See Figure 9.

After checking the toner level three times, and the toner-level state remains low, the toner supply agitator rotates and brings more toner into the hopper. Once the toner level returns to high, the agitator stops rotating.

After the toner-low state is detected 20 times, the printer considers the toner tube empty. See Figure 10.

Remanufacturing the toner cartridge

1) Clean the exterior of the cartridge.

2) With a small jewelers screwdriver carefully pry out the fill plug. Vacuum the hopper clean. See Figure 11.

3) Carefully peel the part number label off the handle side of the tube. See Figure 12.

4) Remove the chip cover with a small jewelers screwdriver. See Figure 13.

5) Replace the chip (be careful to use the correct color chip), cover and label. See Figures 14 and 15.

6) Place a tape seal across the bottom of the tube. See Figure 16.

7) Fill the hopper with the correct color toner, and replace the fill plug. See Figures 17 and 18. The toner tube is finished.

Remanufacturing the drum unit

8) On the front edge of the cartridge, release the two large plastic tabs and two small tabs on either side of the cartridge. Remove the cover. See Figures 19, 20, 21 and 22.

9) On the right (label) side of the cartridge, remove the three screws from the end cap. See Figure 23.

10) Remove the drum cover arm from the left (non-label) side of the cartridge. See Figure 24.

Note that the rest of the drum cover assembly is built inside the right end cap. The end cap, drum axle and drum cover will all be removed as one unit. There is no reason for these assemblies to be taken apart further. Put a piece of tape across the drum cover arm so that it does not come loose and you should not have any problems with this assembly.

11) Slowly start to remove the right side end cap. Do not fully remove it yet as many parts will now come loose. See Figure 25.

12) Remove the PCR by sliding it over to the right and lifting out. Be careful not to lose the PCR holder and springs. They may come loose. See Figure 26.

13) Remove the side screw and waste chamber. This is done after the left side posts are free from the end cap. Turn the chamber up and lift out. See Figures 27, 28, 29 and 30.

14) Slide the right end cap completely off. The drum, drum axle and drum cover will come with it. See Figure 31.

15) Remove the drum from the axle. See Figure 32.

16) Remove the two screws from the inside of the toner hopper. See Figure 33.

17) On the left (non-label) side, remove the three remaining black screws. The single silver screw does not have to be removed. See Figure 34.

18) Lift up on the front edge of the toner hopper and release the three tabs from the back. Remove the hopper. See Figures 35 and 36.

19) Remove the end cap. Note the fuse and flat washer on the metal plate. The fuse needs to be replaced before the cartridge is reassembled (step No. 28). See Figure 37.

20) Remove the bearing from the developer roller shaft. See Figure 38.

21) Press in on the gear side of the developer roller shaft and lift the roller up and out of the cartridge. See Figures 39 and 40.

22) Remove the two screws on the doctor blade. Carefully remove the blade. See Figures 41 and 42.

23) Clean out all remaining toner from the auger and supply roller. See Figure 43.

24) There is no need to remove the gear end cap. Just make sure the gears are free from excess toner. See Figure 44.

25) Install the doctor blade and two screws. Make sure you don’t lose the side contact plate, as it can come loose. See Figures 45 and 46.

26) Slide the non-gear side of the developer roller into the slot on the right side. Pull out gently on the gear end cap and drop the developer roller in place. Figures 47 and 48.

27) Install the bearing onto the gear side of the developer roller shaft. See Figure 49.

28) Change the fuse in the left end cap. The fuse just snaps in and out, no soldering needed. Make sure the bushing and small gear are sitting properly. See Figure 50.

29) Install the left end cap and two black screws as shown. See Figure 51.

30) If the foam seal came loose, replace it now. You may have to condense the seal a little in order for it to fit properly. See Figure 52.

31) Install the toner hopper and two inside screws. Make sure the three tabs are locked in place. See Figure 53.

32) Install a black screw into the end cap/toner hopper. See Figure 54.

33) Slide a new drum on to the drum axle shaft. See Figure 55.

34) Partially install the right end cap/drum/drum cover assembly. See Figure 56.

35) Install the PCR into its holders. See Figure 57.

36) Take the waste chamber and remove the two screws from the wiper blade. Remove the blade. See Figure 58.

37) Clean out all toner. Be careful not to damage the spring auger and felt seal. See Figure 59.

38) Coat the new wiper blade with your preferred lubricant and install into the chamber. Install the two screws. See Figure 60.

39) Install the waste chamber. Install the left side tabs first. See Figure 61.

40) Install the right side end cap the rest of the way. Make sure it seats properly. See Figure 62.

41) Install the two black screws, one on each side, to hold the waste chamber in place. See Figures 63 and 64.

42) Install the left side of the drum cover bar. Test the cover with the arm on the right side to make sure it works. See Figures 65 and 66.

43) Install the three remaining black screws (two on one side, one on the other). See Figures 67 and 68.

44) Install the PCR cover by rolling the top of the cover so the back tab locks in place. Roll the cover down until the front two tabs lock. See Figure 69.

45) Install the toner and shipping locks. See Figure 70.

Remember that new drum units come complete with toner already installed inside the cartridge (thus the need for the toner hopper seal in the drum unit). Because of this, you must include a toner tube with every drum cartridge. Make sure it’s the correct color!

It is also possible that dirty drum unit contacts can cause an issue, see Figure 71 to see the location of the drum unit contacts.

Repetitive defect chart

• Transfer belt 706 mm
• Fuser belt 124 mm
• Supply roller 102 mm
• OPC drum 94 mm
• Heat fuser roller 87.3 mm
• Developer roller 49 mm
• PCR 37.4 mm

Printing test pages

• On the control panel, select INFORMATION, press OK
• Select INFORMATION PAGES, press OK
• Select CONFIGURATION PAGES or SUPPLIES USAGE PAGE, press OK

For sample pages

• On the control panel, select INFORMATION, press OK
• Select SAMPLE PAGES, press OK
• Select the color page and press OK

Common error codes

There are hundreds of different two- or three-digit error codes (too many to list here), but I have included some of the more common failures.

• T1 Upper fuser failure
• T2 Lower fuser failure
• T29 Temperature sensor bad
• T30 Humidity sensor bad
• U18 Yellow LED failure
• U19 Magenta LED failure
• U20 Cyan LED failure
• U21 Black LED failure
• U26 Yellow drum failure. Drum out of position (Up/Down)
• U27 Magenta drum failure. Drum out of position (Up/Down)
• U28 Cyan drum failure. Drum out of position (Up/Down)
• U29 Black drum failure. Drum out of position (Up/Down)
• W18 Cyan imaging unit fuse cut error. The printer detected a new fuse (drum unit) but the fuse did not blow (cut)
• W19 Magenta imaging unit fuse cut error. The printer detected a new fuse (drum unit) but the fuse did not blow (cut)
• W20 Yellow imaging unit fuse cut error. The printer detected a new fuse (drum unit) but the fuse did not blow (cut)
• W21 Black imaging unit fuse cut error. The printer detected a new fuse (drum unit) but the fuse did not blow (cut)
• 940 Waste toner auger rotation failure
• 941 CM toner supply failure: Toner sensor failure with cyan or magenta toner
• 942 YK toner supply failure: Toner sensor failure with yellow or black toner

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Mike Josiah is vice president of technical services at Summit Technologies, a division of Uninet Imaging Inc., and global distributor of toner, OPC drums, wiper blades and other supplies. Josiah has been with the company since 1987. He and his technical support team regularly contribute articles and teach seminars at association meetings and trade shows. Contact him at 631-218-8376 or mjosiah@uninetimaging.com.

This article originally appeared in the September 2007 issue of Recharger.