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]

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

[allan]

Also did you done gradation adjustment?

[fotojohan]

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]

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]

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]

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]

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]

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]

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

As far as the IU:s goes, according to the service manual we're only halfway into the life span on all the units as far as I can tell (CMY= 3610 K=5415)

We've cleaned the PH window with no obvious change.

But I'm thinking that the problem goes beyond the K IU. We're getting intermittent C2557 error – Abnormally low toner density detected black TCR sensor - and the machine makes a terrible racket when printing (sounds like plastic gears grinding). Since this appeared over summer when the office was left unattended and our members had free access to the printer, I imagine that it might have been manhandled by someone causing somethiing more serious than a broken IU…

Image of K IU gears below – top of the teeth look uneavenly worn, but I can't get at the reciprical gear without dismantling the machine as far as I can tell, so can't speak to the state of that one.

C451_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

I'm looking into what a new printer would cost to lease (including service) compared with patching this one together – if getting a new IU would fix it it might be worth it, but the cost of getting a tech out here close to the same per hour as renting a new machine for one month, so we're getting into diminishing returns. Even so, I'd like to see if this is something we can fix or if it's a lost cause.

Any suggestions are greatly appreciated – thanks for your time.

Cheers
Mateusz