[CQ] MP C3500 Strange image defect

[sandmanmac]

I've been asked to help out a colleague who's away for the week.
This problem has been showing up randomly for a week or 10 days.
According to my information, it's very intermittent. It had been at least 2 business days, and a few hundred pages since the last time it happened. The only samples I have are from B&W print jobs, but I was told it happened on B&W copying as well
No parts have been changed as yet.
I can't say for sure what the PM counts are, but the fact that it's so random, has me doubting it has anything to do specifically with Drum life (for example), and otherwise the quality is really good.
I was in the area today and dropped in for a quick look, and of course, couldn't duplicate the problem, and was a bit short on time.
I'm leaning towards something strange happening with the drum unit, but it seems that the shading would be darker
The 3 sample pages were fed LEF and show the progression of the defect.
It's got me stumped, but I thought I'd post it for some input before I just start randomly replacing parts
Image Quality.pdf

[blackcat4866]

Re: MP C3500 Strange image defect

Let me guess: Is the primary charge roller ~12.69mm diameter?

That's about the only part that's going to have a 39.866mm circumference. =^..^=

[NeoMatrix]

Re: MP C3500 Strange image defect

The remains of a label stuck on the a drum.... ?
Could be a drum blade flip just where the label glue is located.

[Counsel]

Re: MP C3500 Strange image defect

Those look like copy defects from a bubble under the white bar, but its hard to tell because you scanned them in, the left side looks like a copy because of the registration being off the dark spot starts almost 2mm into the page while the traling edge goes completely to the edge but that could have happened when you scanned them in to show us, also there is a line at the bottom of the page that looks like dust which also could be from you scanning them in. If this for sure is happening on "printed" images and only on black then I would suggest to inspect the PCU or developer unit. The dev units usually run a pretty long time on that model we only replace them when they go bad but you could have crap on the mag roller, but the PCU's last anywhere from 70k to 100k+ depending on use, if replaced properly each time using the 3902 manual new unit set the meters should be accurate if its over 80k replace the PCU and see if the problem is gone.

If it happens on all colors when running color then check your cleaning unit i try to replace them about 160k or so.

[sandmanmac]

Re: MP C3500 Strange image defect

Let me guess: Is the primary charge roller ~12.69mm diameter?

That's about the only part that's going to have a 39.866mm circumference. =^..^=

This is what I was thinking as I drove away. At a quick glance, there didn't seem to be any defects in the roller, but you're right about the repetition.

The remains of a label stuck on the a drum.... ?
Could be a drum blade flip just where the label glue is located.

Drum looks perfect, and that would cause a constant issue. This issue disappears for hundreds of pages at a time , and then returns for maybe 15-20 pages, then perfect copies again

[sandmanmac]

Re: MP C3500 Strange image defect

Those look like copy defects from a bubble under the white bar, but its hard to tell because you scanned them in, the left side looks like a copy because of the registration being off the dark spot starts almost 2mm into the page while the traling edge goes completely to the edge but that could have happened when you scanned them in to show us, also there is a line at the bottom of the page that looks like dust which also could be from you scanning them in. If this for sure is happening on "printed" images and only on black then I would suggest to inspect the PCU or developer unit. The dev units usually run a pretty long time on that model we only replace them when they go bad but you could have crap on the mag roller, but the PCU's last anywhere from 70k to 100k+ depending on use, if replaced properly each time using the 3902 manual new unit set the meters should be accurate if its over 80k replace the PCU and see if the problem is gone.

If it happens on all colors when running color then check your cleaning unit i try to replace them about 160k or so.

The defect on my original has no lead or trail edge void, and the single line at the bottom was on the pages I received, and I'm not concerned about that.
I'm not sure if its only in B&W, but they do very little colour, and they have not seen it happen with colour prints, and it's so random that it's been impossible to duplicate on site so far.
I'm replacing the entire PCDU tomorrow, and we'll go from there.
Thanks for the input

[slimslob]

Re: MP C3500 Strange image defect

Considering the length of time the MP C3500 has been on the market, I would say that if the black drum unit has not been replaced, it is time to do so. One thing, clean the charge roller then you can try setting SP 3041-001 to 0 and lower the development DC bias by 50 volts, SP2229 for all. This will lengthen the time it takes for the roller to get dirty. It will also reduce the amount of toner on the drum surface that the cleaning blade has to remove. The other thing you can do is adjust the SP settings according the the attached. Service Program (SP) Settings.pdf

[sandmanmac]

Re: MP C3500 Strange image defect

Considering the length of time the MP C3500 has been on the market, I would say that if the black drum unit has not been replaced, it is time to do so. One thing, clean the charge roller then you can try setting SP 3041-001 to 0 and lower the development DC bias by 50 volts, SP2229 for all. This will lengthen the time it takes for the roller to get dirty. It will also reduce the amount of toner on the drum surface that the cleaning blade has to remove. The other thing you can do is adjust the SP settings according the the attached. [ATTACH]32364[/ATTACH]

Thanks Tim.
Very interesting settings. I'll be sure to experiment with them.
The machine has over 1/2 million Black pages, so it's had a few drums units, but with the feedback I've gotten, I'm fairly certain that it needs another one. It was just a bit of strange looking defect, and being so intermittent, it was a bit of a head scratcher, so I thought I'd put it out to the consortium.

[slimslob]

Re: MP C3500 Strange image defect

The spots on the first page could be any one of a number of things. The band on page two and gets wider on page three looks like what I have seen on 6501s when the lube bar is almost completely worn down. Insufficient lubricant on the drum surface causes toner to stick, bypass the cleaning blade, get removed by the apply brush and stack up against the drum on the back side of the cleaning blade.