OKI MC561 black stripes

[skelband]

Hi,
I have an OKI MC561 colour LED printer. CYM are all printing fine. Black has vertical stripes.

There are 4 separate imaging units mounted in a cage. The cage is intended to be replaced as a unit, but they're pretty dear and I would like to learn more about this machine and perhaps rebuild the black unit. The counters are all low so it should be good for thousands of clicks yet.

In the black unit, I have replaced:
- OPC drum
- mag roller

I also emptied the toner from the black unit. The density was poor in the non-stripy area and new toner really improved this.
Still stripy though.

This leaves the PCR roller, which I exchanged with the Cyan one.
Still have the stripes on black.

This is an LED printer so I swapped the LED array units between CYAN and BLACK and still have the black stripes.

I've run out ideas. There's nothing much left in the black imaging unit to swap.
Can anyone suggest what I'm missing?

Edit to add: when I take the black unit apart, the mag roller has the stripes on it which is why I changed the mag roller first, although if I rotate the mag roller, it has even coverage. It didn't make any difference. There is a metal strip which distributes the toner. I wonder if that is the culprit. Perhaps tomorrow I will swap it between cyan and black units. It's really puzzling.

Cheers,
skelband

[skelband]

I also wondered if there is a way if I can check the LED unit output. It's a bit of a long shot but perhaps there is some weird comms error between the black LED unit and the main board causing a drop out where the stripes are. Seems a little unlikely though.

Couldn't find anything in the service manual to allow me to visually inspect the LED array illumination.

[slimslob]

What I am seeing is normally a problem with developer, not the toner which you replaced unless it is a single element toner/developer.

Could also be paper dust blocking the gap between the development roller and the doctor blade. If it is dust from crap paper you will eventually also have the same problem with CMY.

[tsbservice]

If samples are LEF those lines/voids don't look like developer to me. This black led same as color? Are you sure image processing is same?

[Blizzoo]

Yes swap the units and see if the defect moves with the unit. Fro the pictures it seems that the dr blade is the issue here. Use original toner as well.

Normally these units are not serviceable units, must be replaced as a whole unit

[skelband]

Yes swap the units and see if the defect moves with the unit. Fro the pictures it seems that the dr blade is the issue here. Use original toner as well.

Normally these units are not serviceable units, must be replaced as a whole unit

Yeah, the whole unit is usually replaced as a block. Thing is, the counts are super low and all the colours are printing splendidly.

I think the previous owner probably had some really rubbish black toner in there, evidenced by the terrible density.
From the appearance of the toner cartridges, I think they had used bargain basement supplies which is always a mistake.
I vacuumed it all out and put in good quality toner and the difference was obvious. I worried that the crap toner had damaged the rollers and/or drum but that doesn't seem to be the case.

Just looking now, I thought the black unit was different because it also accommodated the waste toner hopper, but I see that is only the toner cartridge. I will swap the black with a colour one to just rule out anything else external. If it is in the black unit, then it really has to be the wiper blade: there is nothing else. Perhaps the black toner damaged it somehow? (which would be sucky since I haven't seen them anywhere separately). AliExpress is the only place to get rollers and OPCs, which seem to be fairly good quality as it happens.

Thanks for the views and comments. Will report back.

[skelband]

If samples are LEF those lines/voids don't look like developer to me. This black led same as color? Are you sure image processing is same?

The LED units are the same part and there is one each for CYMK. They are interchangeable. If I swap black and one of the others, the output is exactly the same.

[richs]

Worked on many OKI machines for many years.I would just replace the drum and make sure you are using OEM toner.You can swap around the leds to check them but I have not had many problems with them.

[blackcat4866]

What I am seeing is normally a problem with developer, not the toner which you replaced unless it is a single element toner/developer.

Could also be paper dust blocking the gap between the development roller and the doctor blade. If it is dust from crap paper you will eventually also have the same problem with CMY.

Like slim, I suspect this is a mono-component machine like the Samsung's I used to work on. The Samsung's had a soft developing roller and a flexible S-blade to meter the mono-component toner into an even layer. Paper dust contamination collects in the S-blade, drawing void lines in the toner on the developing roller.

On these same Samsung's I had changed a few of these toner/developer cartridges, and just out of curiosity disassembled a few. All attempts to clean out that contamination were a failure. The contamination will move around a bit and even diminish if you counter-rotate the developing roller a little, but it always comes back. Even vacuuming the developing housing out completely did not catch the contamination. Replacement is the only effective option. =^..^=

[skelband]

Like slim, I suspect this is a mono-component machine like the Samsung's I used to work on. The Samsung's had a soft developing roller and a flexible S-blade to meter the mono-component toner into an even layer. Paper dust contamination collects in the S-blade, drawing void lines in the toner on the developing roller.

On these same Samsung's I had changed a few of these toner/developer cartridges, and just out of curiosity disassembled a few. All attempts to clean out that contamination were a failure. The contamination will move around a bit and even diminish if you counter-rotate the developing roller a little, but it always comes back. Even vacuuming the developing housing out completely did not catch the contamination. Replacement is the only effective option. =^..^=

OK, that sounds plausible and you're right the construction does sound very similar. It has a one part toner, soft rollers and a doctor blade although the blade seems to be fairly rigid.

I will do some further investigation this weekend bearing in mind your advice.
Before I give up on it totally, I will take the black unit apart and spotlessly clean it all and try again with fresh toner, after I swap the black and cyan unit just to be absolutely certain about the origin of the fault.
I did empty out the toner before but only vacuuming it out from the top. I have not completely cleaned it when disassembled.
Like I said above, I do have evidence that the previous user's toner was very poor: perhaps it was also contaminated with other debris. :(

If that doesn't fix it, I guess I need to splash out on a new unit. I do have some backed up art work waiting for this machine so my patience is running out. :D

[skelband]

Well I tried to strip down the black unit but the hopper section is *really* not intended to be taken apart. Lots of sticky strips and a couple of tabs broken off.
Even a cheapskate like myself knows when to call it a day.

I could try to clean everything and put it back together but there's no guarantee that it would fix the problem and still seal in all the toner.
I have sprung for a new drum unit. They're pretty dear but even with the cost of that, I'm still up. You can't win 'em all.