Bizhub C450 "raster pattern", image quality?

[Kanini2k]

Hi! I'm curious about the image quality on the Bizhub C450, when compared to the older CF3102 the C450 got this very coarse pattern when printing grey colours. I'm not sure if this is a feature or a setting, since all other colours are very even - it's just the grey! The pattern looks like a lot of small "boxes" in the grey areas, like a raster pattern. The other colours are more like dots as it should be when printing for example pictures.
See the attached pics for a enlarged scanned detail of the pattern appeared on grey fields. It maybe looks worse on the scanned pics but the pattern shows more clearly.

I've tried a lot of different driver settings and the pattern appears more or less but never gets as even as on the other KM machines I'm comparing with...

Could somebody just tell me if this is a feature of the machine or a setting/adj. issue before I try to correct it since I don't have any other C450 to compare with. The machine has about 266 k on counter and much life left on consumables. Thank you in advance!!

[xcopy]

When you do half tone test patterns in diagnostics, for CMYK are they grainy

[Kanini2k]

Hi!
Thanks for the reply! Didn't take the halftone test pattern at the machine, but when running gradiation adj. on the calibration sheet all other colors (CMY) seems OK, but black showed the same problem as described with the boxes on the lighter shades... Could take a halftone to test and scan it in a day or so when I stop by the machine again.
The black IU is almost new, so I doubt it's the unit itself...

[Kanini2k]

Halftone test pattern

Hi! Took a halftone test pattern and yes, all other colors are great but the black is giving the same problem, e.g. the "boxes and lines" are clearly visible for example at 55 or 155 density. Enclosed is a pic of for example cyan at 155 and two black prints at 55 and 155 density, and when zooming in at the pic you can see the problem. When printing at full density 255 it's of course not visible and seems OK. It's almost as the "screen angle" is incorrect or something??

[DelawareJim]

You might want to try to reset user modes back to factory settings: Press the Utility button, Store, Reset Mode, highlight the Factory Default, Set.
Something else you may want to try: from the basic display screen press Photo/Density, Screen Pattern, make sure Text & Photo is highlighted, check out Gradation and Resolution......try a copy on each setting.

[Kanini2k]

Thanks DelawareJim, gonna try that to see if there's some setting that's messed up, it at least appears so. I'll get back with it...

[Kanini2k]

Did run a couple of adjustments and it got a bit better after several "reset&stabilize" and grad. adj. runs, but it's not perfect, still the "boxes" or "lines" appear, also on the test pages. The reset you suggested DelawareJim, is that the one that says what mode the copier should go into after copying?? Did set that one to factory defaults, but no change. Didn't find any other factory reset, wich I would be more than happy to try. Is it under service mode? Didn't find it there either...

[mrwho]

Someone please correct me if I'm wrong, but it seems to me that what you have is not a problem or malfunction, but a "feature".

That patterns seems to me to be caused by the fact that the machine doesn't use actual lasers, but a led array to draw the image onto the drums. And the fact that you only see it in black is (I think) either because the black color has much more contrast against the white paper (I believe that if you look closely onto the other colors, you'll see the same effect, only much more fainter).

[xcopy]

The K image is clear on our C450's mrwho.
It is smooth like the other colours.

[mrwho]

Well, it's odd then. It clearly seems like a problem with the Led unit.

The Black LED assembly is different from the YMC ones. Could it be that someone mistakenly swapped the K PH for a color one?

[Albonline]

looking at the output pattern, i'd have to agree with mrwho. the black led is the cause.

[Kanini2k]

Thanks for the replys, I'll better check the machine more troughly then if you suspect the LED unit is bad...

[Kanini2k]

Cloudy sky

I did clean out the LED:s that was quite filthy for some reason, and did run some gradiation adjustment and it kept on getting better and better for every adjustment procedure, so I did run it several times and the greyscale pattern is now quite even and I think I'll leave it like that.

But then I think the cyan IU went shot because it gives the "white clouds" on the middle of a page (see pic), just like it don't get enough toner. Could this be a reason of many gradiation adj. after each other? I've tried to check the drum, seems fine and also filled it up with toner (TCR level check), stabilization, but nothing seems to make the trick easily. This surprises me since the IU is almost new! Is it possible that the IU went shot only by doing the gradiation adj.?

[Albonline]

this does not look good . try sticking a magnitized screwdriver in the waste toner bottle, if you pull out iron, the hv2 power supply is shot.

[time2fly]

Add toner to the Cyan IU not from the service mode but buy putting some toner on a piece of paper and dump it into the IU. Do the same for the BLK. If that works then go through all of the settings (reset and stabilize, etc.). If you still have the same problem with the black swap LED array with another color, the LED's aren't color specific. Good Luck

Also make sure that you clean off the LED's the TDS and the erase lamp along with the charge wire.