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07-26-2011, 11:21 AM
Machine = C451
Fault = Banding lines on black/grey print.

I have a dealer with a 3 year old C451 that has only 187,000 prints on the meter but has a fault when printing Grey images.

test output image plus internal black test print at 125 halftone attached.

As you can see from the attached there are banding lines in the output.

Parts tried to date are:

Black IU
Transfer belt plus transfer roller
Secondary transfer/sync unit complete (from a working machine)
Black IU motor
Transfer belt motor
Fuser drive motor
Fuser unit
Laser Unit11020

We have tried all settings in the machine including changing the productivity to image quality, transfer voltages (ALL), background etc.

None of these made much difference only to make the image lighter or darker but this also effected the banding so was still clear to see.

I need an urgent solution on this if possible please.

07-26-2011, 11:51 AM
Is it just with blk or can you see it on other colours aswell (probably cyan would be the easiest to see it on)?

07-26-2011, 04:49 PM
Is it just with blk or can you see it on other colours aswell (probably cyan would be the easiest to see it on)?

C,M,Y are all ok no banding

07-26-2011, 10:01 PM
Ok, this is a simple (maybe considered stupid) thing to ask... did you run the Gradation Adjust after changing those parts, especially the Black IU?

07-26-2011, 10:41 PM
This is a good one ( so to speak) i would have said blk IU or laser but as you've tried those I guess my next step would be the HV boards or MFP board. Good Luck
Also found this in a release from KM
:)13. Low Image Density
By the pattern on which blue color is lapped over, transfer is bad and image density is low. (There are image lightness and image unevenness.)
[Presumed Cause]
(A) The 2nd transfer voltage is low.
(B) Effect of the usage paper
(The paper currently used in Japan has trend for electrical resistance to be high, and it is disadvantageous for transfer.)
[Basic Action]
The 2nd transfer voltage is increased.
(The reference adjustment value of each paper is indicated to the following page.)
[Service Mode] �� [Imaging Process Adjustment] �� [Transfer Output Fine Adjustment] �� [2 Transfer Fine Adjust] + 1 to 2 steps (It changes a little with papers to be used.)
Reference: 1 step: 100V
*Notice: If +6 steps are adjusted uniformly, there is risk that 2nd transfer voltage will become overmuch depending on the paper to be used, and an image failure, such as an image memory, will occur, please do not carry out that adjustment.
*Notice: If 2nd transfer voltage is lower than the proper value, 10. Toner is sprinkled may also be generated in addition to low image density.

07-27-2011, 01:13 PM
Hi Spratt/Empiru,

in answer to the first question, Yes all grads and stabalize were done and re-done but made no difference.

I am going to try the main drive as it does look mechanical/electrical to me but after that i will start with the HVT.

thanks all for the advice, Why do we do this job again??

10-20-2011, 11:06 AM
so some closure on this one, the files and test copies were sent to the KM product expert in germany who concluded that the machine was within specification and that this is a phenomina with this range of machine, told customer whos not happy but time to walk away.

big jase
10-20-2011, 01:30 PM
strange but true

I did have a same type of fault, went down the same alleys as you replacing everything, and fault turn out to be the customers paper (they were using HP paper) .It had a coating that was coming off to cause the fault. Tried Mondi paper all has been fine ever since.

10-20-2011, 11:07 PM
A long time ago i had the same issue in 2 machines..... i changed all......and......grrrrr.....still having that banding only in black.....one friend told me about replace the toner with a Katun brand , he do that and solved black banding , well....i tryed this and for my surprise it works!!!!! Since that in those machines iīm using Katun toner , and they are running ok........coul be some calibration or charges working near the limit.....donīt know why!!!!!!!

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