View Full Version : Error Code Konica Minolta Bizhub Pro C6501 Error Code C2804

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01-13-2011, 07:05 AM
Hi Frens,

I have encountered error code C2804 with my Konica Minolta Bizhub Pro C6501. It's happening again n again so how to fix it properly.

01-13-2011, 08:22 AM
Have you done any PM lately? what happened before it displayed the error code.

01-13-2011, 01:58 PM
I just had this same code on a 6501, how do your test prints look? If your test prints look good check the color Reg. sensor, cln or replace. Mine ended up being the color Reg Sensor unit. The 2804 refers to black patch error in gamma correction.

01-13-2011, 02:30 PM
Yep, colour reg sensor assembly probably needs a clean.

Also, check that the transfer belt hasn't wandered beacuse this can cause the reg sensors to get pretty filthy.

01-17-2011, 02:39 PM
Thank u all for your kind response after i cln sensors code is not showing now but black print quality is down. It's not like before i mean black color print quality is not good.

01-17-2011, 04:06 PM
Run the colour registration adjustment from the adjustment screen.

01-17-2011, 04:59 PM
Also you can run the recall standard data under process and run all adj. again

08-05-2014, 01:07 AM
i have same problem with C5501,error c-2804.
Week ago it start showing daily c-2804 on startup but simply off/on reslove problem.
Print quality was ok.
Now it can not be turned on anymore, c-2804
I tryied clean sensors first,no affect,then i pull out complete color registration unit,developing unit k and transfer belt and try in other machine and it works ok.
One more thing i see is that on transfer belt after pulling out you can see yellow,magenta and cyan tone line but black is missing.
Anybody can help with possible solutions?
Hv board?...


08-05-2014, 03:37 AM
Hi all,

i also have this code on my C6500, please help

02-28-2015, 09:33 AM
Did this problem ever get resolved? I had a machine this week show the same code. I have been unable to nail it down even after I have replaced everything along the black line although it makes no sense to do. I've replaced the HV board, the reg / gamma sensor unit, charger, drum, dev unit and dev itself. Black is grey(ish). It's dev related problem it seems, but what's the missing link here? Any answers?

03-01-2015, 12:18 PM
check your transfer roller in your belt unit...

usually its the roller worn out of place. Happens when you don't do PM on schedule as you should.

Sometimes I have had to replace the contact which is a pain for all but black. Other times the spring has just gotten stuck preventing contact.

here is the info from Konica...

CAUSE: The transfer roller in the transfer belt assembly has become dislodged.

SOLUTION: Inspect transfer belt assembly and re-position transfer roller as needed.

03-01-2015, 02:50 PM
Thx for your suggestion. I had replaced the transfer unit already with sane result. I can share with you my findings from yesterday as this problem was very frustrating. There was a suggestion to restore to process settings back to factory from another member. Given the limits I had gone to to try and solve this I gave it ago. It worked. It made no sense other then a settings that must have gone corrupt. I was able to calibrate and get the machine back in operation. My concern is the cause is still unknown. I've seen Canon's internal setting go but never a Konica. That was a first.

03-02-2015, 11:38 AM
You need to install a new drum and charging
corona, do in the service mode in Process
Adjustment function Recall standard date [Factory Default Data], then turn off and turn on the machine and make the setting Auto gamma adjustment, I think it will work.

12-07-2015, 04:58 PM
Complicated problem with multiple possible causes and solutions:
Error Code C-2804 - Gamma Correction in Black Failed. Black is the most common color for this to happen. Black gets too light for some reason and the gamma adjustment patch on the transfer belt becomes too light to be read by the color registration sensor. After the machine attempts to adjust charge values for the light black condition for so long, it gets far enough out of adjustment that it cannot recover. C-2804 cannot be fixed without a service call. If the machine is way overdue for a PM with drum and developer numbers above 150% that is the first thing to do.

What might be wrong:

1. Why is the gamma sensor patch too light? or perceived as too light?
a. Run eight copies of test pattern 62 to see what colors are having trouble - might be more than just black.
b. Check the black toner bottle - is it totally empty?
**If it is there may be something wrong with the sub-hopper sensor that detects the out of toner situation. Easiest first step is to bang on the subhopper gently but firmly 5 times with a driver handle. This tends to remove toner caked on the subhopper sensor.
**Put in a new bottle and let the machine tone itself up.
**Run Autogamma0 and see if the code will clear. You might get lucky.
c. Go to Service Mode / Process Adjust / Sensor Output Check and select the toner density sensor readings. Higher number is undertoned. Normal reading is between 125 and 135. Is a dev unit undertoned?
***if black is undertoned with a big number, there must be a reason toner is not being added.
- Is there toner in the sub-hopper? Run I/O check main code 54 sub code 9 to operate the black add toner motor and read the output of the density sensor. Does the number go down? if so toner is being added.
- Does the black toner bottle spin to add toner to the sub hopper? Run I/O check main code 1 and sub code 9 to see if the bottle rotates. Defeat the door interlock. Can be done with the front cover toner section swung out so you can see the bottle.
***Bring any color dev unit back into the correct tone balance by running Toner Recovery Mode
- Service Mode / Process Adjust / Sensor Output Check then Toner Recovery Mode
- Select ALL ON and the machine will run until all dev units are OK - color channels adding toner can be seen by the motor ON indication
- Use the Toner Density Sensor check above to mix the tanks for 2 to 3 minutes after running the toner recovery mode
d. Check operation of the Drum Surface Potential sensor with the machine stopped
***Go to Service Mode / Process Adjust / Sensor Output Check / Surface Potential Sensor - reading for a totally discharged drum should be -002, if larger they should be going down as you watch.
***A BIG number (40 or above) means either the sensor is dirty or something is wrong with it. This sensor does not get dirty, it has a self cleaning charge system. If there is toner around find and correct the problem.
- Clean the sensor (small square hole) with a gray blower bulb or by blowing thru a bent drinking straw (you don't want to spit on the sensor) then I/O check again as above. If you swap the surface potential sensor to diagnose, move the circuit board and sensor as a set.
e. Check operation of the Drum Surface Potential sensor with the machine in motion
***Go to Service Mode / Process Adjust / Sensor Output Check / Drum Surface Potential - with new drums V0 should be 200 and Vi should be 20 to 30.
***These numbers are the result of machine self adjustment. If the drums are the same age the VO and Vi numbers for all colors should be about the same. 25 to 30 points is significant and this number being out of range too far will cause 2804 for sure. Process below will put the machine back in a range where it can self adjust.
f. Is the output of the Max Density (PGC) sensor OK?
***Go to Service Mode / Process Adjust / Sensor Output Check / Max density sensor and same location for the Gamma sensor. Readings are of the sensors looking at the transfer belt. All three outputs should be about the same - 110 to 120 is normal with a reg sensor stamped with a letter N.

2. All is well with the toner system and sensors - First thing to try to get away from the C-2804 code.
a. If the VO and Vi for black in the Drum Surface Potential readings are not too far out of specification you might get lucky and correct the problem by running a standard Autogamma0 adjustment from the Drum Peculiarity button.
***Success will be completion of the Autogamma0 without an error code and Drum Surface Potential readings for VO and Vi in black again very close to the other colors.
b. Maybe you need to run the Gamma Sensor Adjustment if it has not been done for a time.
***Remove the object glass and clean the three mirrors and the back of the glass. They may not look dirty but cleaning makes a difference.
***Run the Gamma Sensor Adjustment procedure - Service Mode / Machine Adjust / Quality Adjust / Printer Gamma Adjust. Print the target for the glass and back it up with 10 sheets of paper.
***Sometimes pressing the Remove Adjustment Data button before doing the adjustment will help
***Run the Autogamma0 adjustment again as the sensor has changed due to the sensor adjustment
c. If the code comes back during the Autogamma0 then go to step 3.

3. Code C-2804 came back and now we know the machine is so far out of adjustment that it needs help to adjust itself.
a. Before doing this step BE SURE the drum surface potential sensors are clean and the toner densities in each dev unit are correct. If they are not and you do these steps the machine may become unfixable.
b. WRITE DOWN all of the settings in the Drum Peculiarity section of service mode ESPECIALLY the LD Bias numbers. You will have to put all these back after you do the factory reset.

c. Go to Service Mode / Process Adjust / Recall Standard Data and choose Factory Initial. Follow the prompts.
d. IMMEDIATELY after recalling factory data, go to Service Mode / Process Adjust / Drum Peculiarity / Autogamma Adjustment and do Autogamma0
***Success will be completion of the Autogamma0 without an error code and Drum Surface Potential readings for VO and Vi in black again very close to the other colors.
e. Recalling Factory data deleted the settings for Drum Peculiarity. Go to Service Mode / Process Adjust / Drum Peculiarity and put the numbers back that you wrote down earlier. I have seen times when the toner density settings create error codes after this is done. If that happens replacing the developer and doing adjustment for that as at PM time is the way to go.

4. Recommend doing the Gamma Offset and Fiery Calibration procedures for best color after this is complete.

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