BH-C-284e, offsetting, would love to have an explanation

**Hansoon** · 4 Weeks Ago

BH-C-284e, offsetting. When printing only one single color, but not black, the colored part of the image is visible as a black offset on the print. Replacing the K-drum unit solves the problem, so I'm happy, but what has the K-drum to do with it?

I know the K-drum is always in contact with the transfer belt and if not clean, there could be a smear on the print which I expect to be random and arbitrarily. Not an offset exactly according to the colored part of the processed image and exactly with a distance of 95 mm from the image, this corresponding to the 30 mm diameter of the drums.

20240323_175314.jpg

See this attachment, where I copied an original using the single color option of the machine. The green bar is at the leading edge.

Hans

**allan** · 4 Weeks Ago

Yea that is strange.

All I can think of is that there could be a latent charge form the yellow and cyan toner on the transfer belt. The black is always running against the TBU and could pick up some of the charge of of that patch causing some toner to pick up from the mag roller or even the toner from the waste just after the cleaning blade. The drum being old could struggle to discharge?

Was the drum well out of life? 15000M+.
You think to much

.

**Albonline** · 4 Weeks Ago

I've seen once where the transfer belt was slipping on the drive roller but only in color mode.

**blackcat4866** · 4 Weeks Ago

Here's my theory, tell me what you think:

The color toners are layered onto the transfer belt in this order: first K, then C, then M, then Y. Black is always the first layer onto the transfer belt on color images, and the last to transfer.

As the machine attempts to compensate for drum wear, during calibration it adjusts many charges: C/M/Y/K primary charge, C/M/Y/K primary transfer charge, secondary transfer charge, C/M/Y/K developer bias, on and on and on ...

I think what you are observing is a poorly compensated secondary transfer charge adjustment, that could easily be caused by any excessively worn drum.

=^..^=

**Hansoon** · 4 Weeks Ago

The color toners are layered onto the transfer belt in this order: first K, then C, then M, then Y.

I do not agree, Cat.

I think it's Y, M, C, and K being the last one before reaching the spot where the TB is meeting the paper and the 2nd transfer station.

Likely, a worn K-drum picks up part of a residual charge from the TB and cannot get rid of it fast enough, so this latent charge attracts toner from everywhere. Probably not black alone but a mixture of Y,M,C,K resulting in this offset image being "blackish" or grey similar to the color of the rest toner in the waste toner container.

Hans

**tsbservice** · 4 Weeks Ago

Originally Posted by Hansoon

I do not agree, Cat.

I think it's Y, M, C, and K being the last one before reaching the spot where the TB is meeting the paper and the 2nd transfer station.

Hans

You disagree but essentially said the same as BC and that's correct.

**Tech09** · 4 Weeks Ago

Originally Posted by tsbservice

You disagree but essentially said the same as BC and that's correct.

I believe he was just disagreeing with the order of toner being laid down on the transfer belt.

**copier tech** · 4 Weeks Ago

Originally Posted by Hansoon

BH-C-284e, offsetting. When printing only one single color, but not black, the colored part of the image is visible as a black offset on the print. Replacing the K-drum unit solves the problem, so I'm happy, but what has the K-drum to do with it?

I know the K-drum is always in contact with the transfer belt and if not clean, there could be a smear on the print which I expect to be random and arbitrarily. Not an offset exactly according to the colored part of the processed image and exactly with a distance of 95 mm from the image, this corresponding to the 30 mm diameter of the drums.

20240323_175314.jpg

See this attachment, where I copied an original using the single color option of the machine. The green bar is at the leading edge.

Hans

The black imaging unit is always being driven & has a charge even if only doing single colour. So if the drum is worn you will get black marks / lines.