C451: no saturation in blacks

[fotojohan]

We are having problems with washed out, faded prints on our Konica Minolta C451, and it's specifically K that is grey rather than black.

As you can see on the image, black doesn't go all the way to 100%, it also makes a weird shadow/line around the darkest parts. After taking out the black imaging unit (not sure it's the correct name for the part) and vacuuming behind it, the black strangely enough behaved slightly better, and printed one more stripe towards 100% black.

Any ideas on what might be the problem...?

Skärmavbild 2019-09-18 kl. 17.20.49.jpg

[tsbservice]

Re: C451: no saturation in blacks

Clean laser slit, post parts life span, looks it's time for changing K drum/developing unit.

[allan]

Re: C451: no saturation in blacks

Also did you done gradation adjustment?

[fotojohan]

Re: C451: no saturation in blacks

Clean laser slit, post parts life span, looks it's time for changing K drum/developing unit.

Hmm, what's laser slit? You're talking to an amateur here...

[fotojohan]

Re: C451: no saturation in blacks

Also did you done gradation adjustment?

No I haven't, I think I found it in the service menu, but it was just columns with numbers that I didn't spend time trying to understand. Is there a guide for doing it or so...?

[tsbservice]

Re: C451: no saturation in blacks

Hmm, what's laser slit? You're talking to an amateur here...

I know...but I'm in good mood right now
Laser slit=PH window, use cleaning jig.

[fotojohan]

Re: C451: no saturation in blacks

I know...but I'm in good mood right now
Laser slit=PH window, use cleaning jig.

Is this the little hole beneath the drum? Where the plastic stick with the felt tip (cleaning jig?) goes in?

[tsbservice]

Re: C451: no saturation in blacks

Is this the little hole beneath the drum? Where the plastic stick with the felt tip (cleaning jig?) goes in?

Hey here isn't tech support chat. We don't get paid for answering questions at CTN.
What about parts life? Post it here if you want more information.

[raplma]

Re: C451: no saturation in blacks

Back in the day we had 6 of these machines - and we loved them - some of which were doing 90k plus per month, and one even reached over 6M before it finally died, so for us they were good machines.
It was very rare for the black IU to go to life and rather common especially on the early models to dump the black dev all over the write unit/print head lazor.
IIRC there was a very slight modification to the blue clamp which reduced the chance of this failure.
We could get double life out of a fuser and if careful a TB, but IU's rarely went much over life and for image quality and machine longevity replace them when EOL.
Our machines suffered from the effects of dust, tonor dusting, and so we regularly cleaned them out, especially the IDC sensor, as well as using the pad on the long grey stick to clean the lazor glass.
If you are new to these machines, may I suggest using Google and search for "Konica Minolta c451 Field Service Manual", all the time spent familiarising yourself with this will be well worth it.
Also search for the "theory of operation" manual as this will give you a start in how these machines are able to print, which comes in handy when something goes wrong you have a better idea of what part of the process is faulty and so you have an idea where to start.
As already said the more info you give the better it is for someone to give more specific help.
I would clean the IDC sensor, if that doesn't help, replace the black IU.

[pozar]

Re: C451: no saturation in blacks

Hiyall, thanks for the replies.

I'll pipe up since I'm poking this machine as well.

Consumable status print shows:

• Imaging unit C: 1963
• Imaging unit M: 1510
• Imaging unit Y: 1491
• Imaging unit K: 2749
• Fusing unit: 141546
• Transfer roller: 141781
• Image transfer: 171748
• Ozone: 141781

Abnormally low toner density detected black TCR sensorC451_K_IU_gears.jpg

Troubleshooting C2557:
We've done the first two steps below to the best of our abilities, but I haven't looked into getting to the toner supply motor onwards.

1. Perform image troubleshooting procedure if image density is low.
2. Clean the TCR sensor window on the underside of the imaging unit if dirty
3. M12 operation check
   1. (At this time, IU must be non-installation.)
   2. PRCB CN16PRCB-13 to 16
   3. C-22
   
   
4. M14 operation check
   1. PRCB CN17PRCB-9 to 12
   2. K-1
   
   
5. Reinstall imaging unit
6. Reinstall toner cartridge
7. If the toner empty sensor and its surround- ings inside the sub hopper are dirtied with toner, clean them.
8. Change imaging unit /K
9. Change PRCB

[allan]

Re: C451: no saturation in blacks

Take a big old spoon full of toner and chuck it down the Dev tank shoot and print 5 test pages. Keep an eye on the TCR K value under <state confirmation> <level history 1> and see if the TCR value goes up.
If it does the TCR sensor is fine. Your C-2557 will go away for a short run of print but will return. Normal value is at 6.5% yours should be at 4% to get the code.
Meaning that the sub hopper thinks its full and supplying toner but its actually not, or it is but no way for the toner to escape. Check if there is toner in the sub hopper. That would be point 7 in the trouble shooting describing toner stuck to the toner detecting sensor.
Strip an clean sub hopper.

For your noise hardened toner in the sub hopper could be the issue.
But then again on these machines it could be the transfer belt cleaning unit.

If the TCR value is like at 0% them it could be the IU.

[pozar]

Re: C451: no saturation in blacks

Take a big old spoon full of toner and chuck it down the Dev tank shoot and print 5 test pages. Keep an eye on the TCR K value under <state confirmation> <level history 1> and see if the TCR value goes up.
If it does the TCR sensor is fine. Your C-2557 will go away for a short run of print but will return. Normal value is at 6.5% yours should be at 4% to get the code.
Meaning that the sub hopper thinks its full and supplying toner but its actually not, or it is but no way for the toner to escape. Check if there is toner in the sub hopper. That would be point 7 in the trouble shooting describing toner stuck to the toner detecting sensor.
Strip an clean sub hopper.

For your noise hardened toner in the sub hopper could be the issue.
But then again on these machines it could be the transfer belt cleaning unit.

If the TCR value is like at 0% them it could be the IU.

Thanks for the help all, but we solved the problem by leasing a new machine with service included - yay all around! (thread about that here