Bizhub C350 - Printing quality problem - Gaussian blur and fade out

[Le Wins]

Hi there!

I just bought a used/older laser printer - Konica Minolta Bizhub C350.
Its working but I got some printing quality problems.:
In places where the lines, pictures or text are thick, dark, dense or crossing each other the printer make some… gaussian blur like spots/smudges. And also on the opposite, where the printed elements are thinner or pale, some parts are faded out completely. Printing a file or scan/copying something yield the same result.
I got a guess what causing it but for sure, I ask you opinion.

 

[PeterBJ]

Do you have the service manual? You find one here, maybe it will be useful? See page 243 and on for troubleshooting.

 

[The Hat]

I just bought a used/older laser printer - Konica Minolta Bizhub C350.
Its working but I got some printing quality problems.:

Often when these office laser printers has issues they tend to be mothballed and removed from service because their near the end of useful life or the owners can’t afford the down time getting them serviced.

You could be luck and it may have only some small issues, but if that’s not the case then the costs of servicing will mount up rapidly, so your either in for a quick and easy result or you’ve just fallen into a money pit.

I’ll PM you with a PDF of mono laser diagnosing image issues, if might not help but it may give you an insight into where to start looking with your colour laser.. of try @PeterBJ advice..

 

[Le Wins]

Thank you for your reply.
Here are more samples.
Meantime I managed to set up the scanner, printed a Printer Test Page, scanned/copied a picture and also I made a custom test page with different line thicknesses/sizes, with different transparency and with the primary colors, just as suggested. It seems to me that the objects size and transparency has to be very specific, otherwise the quality is poor. It applies to all colors in same way.
The printer started his “career” 04.04.2006, accordingly the service log book. By the way the log book is pretty plain. The only useful information (at least for me) is the list of changed/repaired parts, but there is no dates listed.
The last part was HD-501, an hard disk, according the service manual.
As a start I watched a video from an Italian YT channel (viandant5) about common print quality issues. It was very helpful but sadly none of the examples are similar to my issue.

Thank you for the manual, I will get trough the troubleshooting.

Thank you The Hat for the PDF. That is exactly the thing what I searched before. But also none of these examples apply to my problem.
Actually I bought the whole thing for 20euros and also get some free original toner with it. If I wouldn’t be able to repair it in the end, reselling the toners should cover the cost.

 

[The Hat]

But also none of these examples apply to my problem.

I’d hazard a guess that the colour units are out of registration with one and another or the transfer belt is loose or very worn leading to bad timing, so I would concentrate my effort on that to start with..

 

[Le Wins]

Thank you The Hat

unfortunately this example doesn’t apply (in my opinion) to the symptoms my printer has.
But anyway I recommend checking it out if you have printing quality issues. It could be very helpful.



Edit:

 

[Le Wins]

Some news
I got some denatured ethyl alcohol so I attended to the cleaning of the transfer belt… but I got another issue. I can’t get out the transfer belt unit because replacing procedure for the transfer belt does not make any sense. The manual is showing something else on the picture compared to what I see in the unit.
Also I found two versions (so far) of this manual but neither of them make sense.
1. I removed the imagine units, as written – no problem.
2. Removed the waste toner bottle – also no problem.
3. Removed the two screws on the sides of the belt unit – also no problem
But as the next step there should be some release lock which I don’t see anywhere. (Compare the pictures)
Other things:
I checked the Unit life indicator (see the picture). I don’t know how seriously I should take indicator, in simpler machineries this kind of statistics can be fooled/resented/altered but I don’t know does it works in this devices.
Accordingly to the service manuals I found 3 “typical faulty image” examples which are similar to my case, on pages 4-60, 4-80 and 4-97.
The 4-60 mentions scanner/copier parts/issues, and because my problem affects printing also I exclude those solutions.
The 4-80 mentions LED assy and imaging unit.
The 4-97 mentions fusing unit relates problems. Fiddled with the fuse speed, either increasing or decreasing it but made no difference.

By the way, changing the transfer belt unit would be a costly operation. In our country it goes around 450-400 euros, from china around 200 and if I want to change just the belt maybe around 70 euros. Which opens questions for me: Are the OPC inside the printer interchangeable? (Cyan with magenta or black for example…) Which parameters should I check for compatibility at transfer belts and OPC drums? Dimension of course matter but for example, is this belt spare part compatible with my C350? According to this page C350, C351 and C450 uses the same unit with the same belt I guess.
In a matter of laser printer I am a newbie, but I got some experience in repairing other electronic and mechanical things. Based on my experiences and the basic understanding about how the laser printers work I got some conjecture.
I got no references to this blur issue but it resembles something which I imagine that can happen with magnetic fields and electric charges. The blur either appears between dense/thick/intense objects (like between letters) or around thick/dense/intense object which haves no white spaces inside. Because that, I guess whatever causes it, it is related to electrical charges/magnetic fields and the ability to hold them. It is like the problematic parts ability of holding the charge is decreased and because of that the charge flows/jumps away of the basic area, pulling some toner particles along with them.
Is there any option where the voltage/charge level can be adjusted of some parts? I would like to fiddle with it.

 

[Le Wins]

I didn’t find any primary or secondary transfer voltage options in the service manual, but found other three promising options PRT Max Density, PRT Highlight, Background Voltage Margin (The words Text gradation and foggy background catch my eyes) I tried either increasing or decreasing the values and run stabilizer in one case along with them. It didn’t help. I tried different gsm paper types, adjusting ATDC Levels, in Color Balance Settings the Saturation, Brightness Contrast, Sharpness. Neither of these options made significant/recognizable changes to the problem.

 

[The Hat]

By the way, changing the transfer belt unit would be a costly operation.

I reckon you’re going to need a new printer.. And move on, that’s what the previous owners did…

 

[Le Wins]

I don’t give up such easily

The unit is working. Even though it has quality issues we cans till use it for probably half of the things it was intended for. It still worth me to sped 100-200 euros for parts, but I need more information which ones to order.