Black Marks on Bizhub C450

[seniortech]

I have a Bizub C450 that is giving intermittant black marks on copies/prints. they are what I can only describe as large faint (1cm) irregular shaped spots appearing completely at random; they could appear anywhere on the print/copy, the spots are fused on the paper and do not flake away, it seems almost like background, the machine has only done 100K.

This very same fault appeared about two weeks ago but I was not involved; another collegue visited the machine, but the fault had disappered before he arrived.

I have removed all units, checked paper path/guides etc for toner contamination, I have tried various diagnostic tests and ran 600 prints/copies on various paper without problems; the fault then re-appeared for 50 or so copies then disappeared again. All test prints in diagnostics show ok.

I am going back tommorrow with another black I/U, transfer rollers/complete transfer unit for another crack at this one as the customer is now getting 'jumpy'.

Has anyone here had this sort of problem? I will try and get an example uploaded but won't be for a couple of days.

Thanks

[AusiTech]

Sound Weird.. I have had the blk LPH unit fail many a time causing all sorts of differnt issues. Maybe try that.

[Huminaboz]

I am receiving a similar problem on the c450 where I work. The specks look like this:



It occurs on -any- thickness of paper if the printer is set to print thick 1 or up. It is fine on normal paper, for the most part (sometimes it cuts off a section of a letter).

[just a tech]

maybe a possible transfer problem...not sure..

[CMB]

could it be the paper? i have a short list of paper types that will be garanteed by KM to run thru the c-450 without copy quality problems.. all other types are not garanteed. try changing paper. i'll try and post that memo soon.

[seniortech]

Eventually I replaced the complete transfer belt unit as I could find no obvious cause. I then fitted the old transfer unit to another machine and the fault then appeared on that machine.

[Huminaboz]

It appears that under the tech settings, someone set the
Image Process Adjustment
Background Voltage Margin
Black to 5+

Once it was set back down to 0 with the others it began printing fine.

It seems that setting the printer to Thick 1 or above increases the voltage naturally, so when any type of print setting above Thick 1 was chosen, it would overcharge the black and make it "explode" on to the paper. Or simply print improperly.