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09-01-2013, 04:26 AM
I recently purchased a KM C451 machine and it worked fine until I did app. 200 prints on 160g/m2 mondi color copy paper.
Then it started leaving huge stains (of only black toner) on one half of the paper (pdf 21919))
I was printing with Thick2 settings from tray4 (but looking into service mode there are no differences for different kinds of paper - all settings are on 0).

I looked into the machine and since then there is black toner on the black IU. I cleaned it and at next test same thing happened again. See pictures bellow.

Machine has app. 350.000 prints, all info about consumables seems they are in good condition. It worked fine before using thick paper.
Can anybody, please, give some advice?
I am not a service expert but have been working with these machines for 2 years and know how to handle some basic stuff.

Thank you.


09-01-2013, 11:51 AM
Looks like you have someting stuck in the evacuation mouth between IU and toner rezidual transportation.Did you dissmember the IU and clean the whole unit under the cleaning blade?is the problem reapear in the same place after cleaning?

09-02-2013, 01:25 PM
You have compatible toner in the machine, i have seen this on numerous occassions.
It will be fine if you clean it a few times. After a while it settles down.

09-02-2013, 09:05 PM
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09-03-2013, 12:06 AM
oh dear, a c451 destroying black imaging units, how unusual, not.

not all that uncommon, if its an on going issue in the machines history and assuming the machine has the locking plate securing the black imaging unit in place and the transfer belt is perfect its probably time to change HV1.

You may of just been unlucky and the transportation of the machine (if you just got it) can cause this to happen too.

I'd be pissed either way with this happening on a recent purchase, I hope they sort it out for you as those black imaging units are close to a grand each.

that fault you pictured can be caused by a genuinely faulty imaging unit but more often than not, the machine itself.

09-15-2013, 08:23 PM
First, I would like to thank to some of you who shared and gave advice about this problem based on your experience, some trough private messages.
This is also the reason I would like to share the result of aou case.

After some cleaning, adjusting and couple of days without the problem repeating itselft, I can confirm that the reason was slightly unevenly adjusted cleaning plate (the distance from drum was uneven for couple of 10's of mm, but seen with base eye) that caused strange loading of developer's material. It is a used machine and obviously black IU was modified by former owner - when we tried to adjust it to be more even, it coused much bigger problems and we decideed to put it back. It produces slighlty lighter black on one side of the paper, but for our pusposes that is not critical so we decided not to change the IU.
It was some error in machines' adjustments after printing on thicker paper - combination of power supply and IU's cleaning blades' position.
Though the service guy said that printing on 160g paper with Thick2 option should not have caused this problem.

It s also possible that this job in a combination with this issue caused it:
"Date: 05/21/10From: SSD
Subject: Dirty Images, Black Developer Spew - MANDATORY CHANGE
bizhub C451: 073 bizhub C550: 082 bizhub C650: 066
Supersedes Bulletin #7370 dated 3/29/10. Revised to eliminate reference to customer instruction. For machines where end users
replace the IU, refer to Bulletin #7461.
In some cases, prints may be either partially or completely covered by excess toner, creating a dirty
appearance. At the same time, developer may have spewed into the machine.
Poor electrical contact of the charge terminal at the back of the IU results in improper operation of the drum
charge control. This causes too much charge to be applied to the drum, resulting in dirty images. Poor contact
can occur if the IU is not seated firmly and securely."

The plate is on the machine and holding the IU well, but it seems that this issue causes some similar results.
Worth checkin'.

To conclude:
- installed plate (Bulletin Number 7370) is mandatory if you have IU this old
- if plate is installed, check for settings and position of cleaning blade
- possibly power supply of IU

Thank you for helping resolving the problem.

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