[Dead] Bizhub C652ds white dots in blacks

[mntech]

Hey guys,
Black developer unit and drum unit were just replaced, the machine ran great for a few thousand clicks, now i have white dots showing up in just the blacks. CMY looks fine. There is no repetative pattern to the dots, and i dont see anything wrong with the drum or dev.

Mag roller doesnt look like it has an contamination, and the problem doesnt change after running sky shots.

I'm leaning towards dev unit as culprit, but i dont know why a brand new unit would cause such a problem.

See examples.\

Thanks,
-MNTECH

bizhub_c652ds.pdf

[allan]

Re: Bizhub C652ds white dots in blacks

Check if the primary transfer current is set to default.
Try switching on DEV AC BIAS.

[Flash]

Re: Bizhub C652ds white dots in blacks

Replace the transfer belt especially if you have been resetting the counter instead of replacing it.

[mntech]

Re: Bizhub C652ds white dots in blacks

I believe the transfer belt has only been reset once, and is only around 25% over life, and surface looks great, no lines/grooves. One would think transfer belt would cause problems with all colors...not just black.

I believe the primary transfer current is default but I will double check. what does the dev ac bias setting do?

[allan]

Re: Bizhub C652ds white dots in blacks

Don't know exactly. Was told in training to switch it on it i get white spots on solids.
could be developer unit or the drum. Check the K TCR value in state conformation level history 1.

[mntech]

Re: Bizhub C652ds white dots in blacks

I don't ever recall seeing a setting called dev ac bias, is the setting you are talking about the dev bias choice?

I never knew what that did, but I do know when that is turned on, the user no longer has the ability to do a calibration

[copier tech]

Re: Bizhub C652ds white dots in blacks

Have you got any P codes showing?
Dont rule out the ITB unit especially as you say it's way over life!
Also the PTR that replace that with ITB

[mntech]

Re: Bizhub C652ds white dots in blacks

Fixed!

Changed primary transfer setting from 0 to -6 for black and the white spots went away.

At first I increased the setting and spots got worse. Also the dev ac bias setting didn't make a difference so I left it off.

Do you think I should replace the transfer unit or just run it with at -6 until there are more problems?

Thanks for all the help

[Laserbeam]

Re: Bizhub C652ds white dots in blacks

Hi mntech,

yesterday I had exactly the same problem with a bizhub C552

First I replaced the drum without success, then the developing unit, but this phenomenon still occurs.
As you see in the attachments, one picture shows a halftone printout with a value 255, the other with value 70. On the halftone-printout (value 70) are much more white dots visible than in the other.
Tomorrow I will change the primary transfer setting value, as you described it.

Or is there in meantime already another solution?

[Laserbeam]

Re: Bizhub C652ds white dots in blacks

Today I cleaned at first the metal contacts of the transfer roller, then I replaced the roller with an new one. The white spots were no longer visible. Now the halftone image in black is perfect!!!!


When I increase the primary transfer setting from 0 to +1 for black, only a few spots are visible. Now I changed the value to -1