White Horizontal Chaotic Strips-gaps (Bizhub C227)

[staraseko]

Dear comrades! Absolutely incredible things are happening on my Konica Minolta C227 printer, I can't even make sense of it.
Horizontal (across the paper direction) chaotic WHITE stripes have little-by-little appeared. But what a kind of stripes!
1) There are NO chaotic stripes in black-and-white printing. They appear only when printing in color, and then they affect the black color as well (!).
2) These stripes (gaps) appear on each color separately AND sometimes on all colors simultaneously (this is not random coincidences, but exactly “global” all-color brightenings).
3) Even more incomprehensible are the results of the Stop-test: the image looks perfect on the drums, but it is already stripped on the transfer belt. My first thought was that the toners are mixed inappropriately. But I tried colors in all combinations, tried separate colors C, M, Y, K, and without any mixing colors everything is the same: everything is fine on the drum, but striped on the belt. Let's assume that the transfer belt makes a skip in these places; but there are also the gaps of only one color! So, the belt is normal…

Test page on A4 along:
IMG_20240326_191111000.jpg

Interrupted printing on an A3 sheet (most of it is unfused, so there is not much black there):
IMG_20240326_191202000.jpg

(You can see on the black color a vertical pale stripe and even horizontal rhythmic gaps with the circumference of the charge roller, but I think it is not related to the topic: these small noticeable gaps appears even in the black-and-white printing, they are understandable, they are also manifested on the drum, and it does not bother me yet - it can't be the cause of unexpected chaotic stripes in pure blue or pure yellow areas where there is no black toner at all).

Just in case: toner, developers and transfer belt are compatible, but the same problem can not appear simultaneously in all colors!
If the belt is bad, why are there the stripes individual for each color? And if all the developers are bad, - why there are the stripes global for all colors at the same time?
For a test I put a bad drum for black color (together with another drum-unit and chip) – so, all-color gaps appeared even in the places where the drum terribly smears and never prints light. But these gaps are - white! How so?!

The gaps appeared little by little and became more and more frequent and wider, in about 500 or 1000 prints.

[kingarthur]

it looks to me like you have dirty printheads, all of the colour ones need cleaning. the reason why the "black" has strips when printing in colour, is because it's using all the colours to make the black

[Gift]

Looks like HV fluctuations / issues - might be caused by worn out/defective consumables or bad contacts.
It's not unusual that one issue can sort of backfire over multiple colors since some HV voltage generators provide multiple units.

[staraseko]

it looks to me like you have dirty printheads, all of the colour ones need cleaning. the reason why the "black" has strips when printing in colour, is because it's using all the colours to make the black

Do you mean laser glass? Of course, it is first that I did: cleaned up all laser glass. But dirty laser makes white strips ALONG paper path, and we have ACROSS.

Black uses all colors, INCLUDE BLACK toner. My black has gaps, in which I see yellow or magenta color, that's why black toner has his own gaps. (which are absent in B&W printing)
And! Black colors are generally white in "general gaps" (which also are absent in B&W printring).
Gaps are along ALL 4 colors (!)
I can't understand it.

[staraseko]

Looks like HV fluctuations / issues - might be caused by worn out/defective consumables or bad contacts.
It's not unusual that one issue can sort of backfire over multiple colors since some HV voltage generators provide multiple units.

This is very similar to the truth. I've noticed that one bad contact in drum-unit of ONE color can affect ALL colors in unpredictable ways. It's because of HV fluctations.
Firstly I will disassemble all drum-units to clean all contacts and write down result. And then will go to HV contacts. Thanks! It is good idea.