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Color 8500: Repeating Color Image Problem

17 Feb, 2002 By: Steve Geishirt imageSource

Color 8500: Repeating Color Image Problem

One of our account
reps, Dan Cassidy, stopped by my office a little while ago with an image defect
problem that a customer of his was boggled over. He was getting a repeating
image across the page and had replaced the image drum and transfer kit to no
avail. Seeking more information, the customer faxed us a copy of the problem.
The repeating image was a little over two inches to the right of the color print
on the page, (figure 1). The strangest part about the image defects was that the
customer said the repetitive print was only in color - there was no repetition
in black. Because of this, the customer was thinking it might be a laser scanner
problem or DC controller failure. However, the solution was a lot simpler and
less expensive than what the customer first suspected.


In order to trouble-shoot this, we had to remember the image the customer faxed
us was a letter size page, which meant the paper physically went through the
printer long edge, or sideways. Thus, seeing a repeating image trailing about
two inches to the right of the print actually meant it was repeating about 2
inches down the normal image path or paper path. Turning the page a quarter turn
clockwise, produced the image as it was made in the printer. The next step in
trouble-shooting this was using the repetitive defect ruler - a good tool found
in the service manual. The distance between the repeating image on the fax was
the same as on the customers print, and measured 56mm or 2 and 3/16 inches. The
measurement pointed to the cleaning roller as the cause of the repetitive
images. The next closest measurement to the cleaning rollers was the black
developing roller, 52mm or 2 and 1/16 inches. Since black was not repeating at
all, the roller was ruled out.

Ruling Out

Since we suspected a possible cleaning roller problem, we started by looking at
its specific purpose. After four layers of toner are placed on the transfer
drum, paper moves through the transfer section, pulling toner off the drum and
down onto the paper. As this is happening, not all the toner leaves the transfer
drum. The cleaning roller is engaged with the transfer drum at this time and
changes the charge of the residue toner so it will be attracted back to the
image drum. Once the residue toner is on the image drum, a scraper removes it
from the image drum sending it to a waste toner collection area, (figure 2). At
the completion of the cleaning process, the cleaning roller is pulled away from
the transfer drum and allows the new image to be created for the next print.

Replacing the
cleaning roller in this case did not fixed the customer’s problem when they
installed a transfer kit, but the customer was in the right area. As noted
above, the cleaning roller engages with the transfer drum when cleaning and
disengages from it when it is finished. This is controlled by a solenoid, SL 1.
If by chance the cleaning roller stays engaged with the transfer drum when it is
not supposed to be, the cleaning roller will pickup whatever toner is on the
transfer drum, and by rotating around, paste it back onto the transfer drum.
This would create a repeating image across a letter size page with a distance of
2 and 3/16 inches, but if this is the case, why isn’t the black toner
repeating too? 

A Look Into The
Transfer Process

To understand this, lets focus in on the transfer process where the image is
being transferred to the paper. Lets assume the cleaning roller has been in
contact with the transfer drum through the whole image formation process. As
each layer of toner is placed on the drum one at a time (yellow, magenta, cyan
and black), the cleaning roller is creating repetitive prints of it on the
transfer drum. As the third color, cyan is placed on the transfer drum, the
image rotates around, and the cleaning roller creates a repetitive print of the
three colors. Then, the black image is placed on the transfer drum by the image
drum. As black is being put on the transfer drum, the paper feeds through the
machine and the image is transferred to the paper. The transfer happens before
the black toner gets to the cleaning roller, so the only colors that repeat
across the page are the yellow, magenta, and cyan. 

The Stopper Arms
And Tension Spring

The problem here is obviously the physical contact of the cleaning roller when
it is not supposed to be, but why is it doing this? There have been problems
with what is called a stopper arm, which works with SL 1 to engage and disengage
the cleaning roller. If the stopper arm breaks or the tension spring that keeps
the arm in place is missing, the roller stays engaged. To locate these two
parts, you need to remove the transfer drum. Open the front door and unlock the
transfer drum via the large green handle. Next, open the right door and remove
the transfer drum by grabbing hold of two green handles. Looking back inside the
machine on the side that the transfer drum was removed, the black cleaning
roller sits above and parallel to a yellow sticker, see (figure 3). To the right
of the cleaning roller, you should see a white plastic arm with a tension spring
attached to it, see (figure 4). If the spring or part of the white stopper arm
is missing, you’ve found the problem. You may be able to push against the
cleaning roller and notice it moves in and out about a half inch or more (if it
is working correctly it should not do this). This is not a sure-fire test to see
if the cleaning roller is functional, but when these parts are missing or
broken, it is often a good clue.

The replacement
parts numbers are not listed in the service manual, but it might be a good place
to write them down for future reference. The stopper arm is RB1-9891-000 and
tension spring is RS5-2699-000.

The rest of this
article will be dedicated to the procedures to remove and replace the stopper
arm and tension spring.

Turn off the printer and unplug it. Remove the transfer drum by unlocking it via
the large green handle inside the front door and then removing the unit from the
right side door.

2. Remove the cleaning roller by pulling on the shaft from the right hand side,
(figure 5). Do not pull the roller out more than one inch as this may break the
bushings on the other side. Slide the roller to the right and remove it from the

3. Next, release the coil springs from each side of the cleaning roller holder
by taking the spring tip and sliding it toward the center of the printer,
(figure 6).

4. Rotate the white bushings next to the coil springs until the flat spot on the
inside part of the bushings is facing down. The bushings are keyed and when
rotated into this position, they will allow the cleaning roller holder to slide
toward you, (figure 7).

5. Locate the tension spring attached to the white stopper arm (figure 4), if
still attached, and remove it.

6. Remove the stopper arm by first removing the E-clip to the right of it.
Carefully, unclip if from the shaft being careful of where it may land. Next,
slide the shaft that holds the white stopper arm toward the center of the
machine, slide the stopper arm to your right and remove it, (figure 8). If you
damage the e-clip, it is a standard size and part number XD2-1100-502.

7. Installation is the reverse of the procedure.

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