C-2557 caused by a filter

I had a worrying call about a Bizhub 362 that was getting C-2557 errors. A C-2557 error on a Konica Minolta copier is caused by the Toner Concentration Ratio (TCR) sensor in the black developer developer unit reading too high. The TCR sensor reads how much toner is in the developing unit and allows the machine to control the toner level by adding toner. But if the level is too high the copier can't easily remove the toner from the developer mix and so an error is generated. Sometimes the high reading is actually caused by too much toner in the developing unit but usually by old developer mix or a faulty sensor causing a bad reading.
However the machine I am looking at doesn't have any of those things wrong with it. How do I know? Because I changed the developing unit only a month ago. Also the error only occurs during longish print runs (50 pages) and if the machine is allowed to sit for a few minutes and turned off and on again it will work fine until another long print run is started.
I went into the service menu and had a look at the TCR sensor values and they seemed normal and then did an F8 just to be sure. No good.
While waiting for the F8 to finish I went and had a look at the Konica tech bulletins for this model and found an interesting bulletin all about this very problem. The Konica boffins mention that if the ozone filter is blocked it can cause the error. So I pulled the back off the machine and pulled the filter out and sure enough it was full of dust. I vacuumed it out and the other filters while I was in there and put the machine back together. I gave it a test and no more errors!
It seems that the restricted air flow through the filter was causing the imaging unit to overheat during longer prints and then the TCR sensor would start giving higher readings until it failed.
So just because the filters are hard to get to doesn't mean that you should ignore them. Clean your filters!

C-2255 after IU replacememt

I had a slight problem after changing the colour imaging units (IU) in a Bizhub C754e. The 3 IU had reached the end of their lives so I pulled them out and put a new set in. The machine then displayed that an internal error had occurred and rebooted itself twice. Still failing the machine displayed a C-2255 error and gave up. I pulled up my list of trouble codes for these machines on my phone and had a look but this code was not on this list!

Don't panic yet.

I have a list of trouble codes for the C364e on my phone as well and the code is there. Developing unit motor failing to turn. Obviously one of the new imaging units had a problem with its developing unit that was causing the drive to lock up. Not the first time I had seen this so still no need to panic.

I started from the left and pulled the yellow IU and used my pliers to give the developing drive coupling a turn clockwise on the back of the IU. It was jammed.

Sometimes the developing powder in the unit can settle in transport and jam the augers inside the unit. Giving the unit a few taps on the side while turning the coupling quickly freed it up and I stuck the unit back in. I pulled the other two out but they felt ok and went straight back into the machine. I then went through the gradation adjustments without any more problems.

I will point out though that if you have this problem you need to be careful not to shake up or spill any developer out of the new unit as you will not be able to use it and it will need to be replaced. Also be careful not to turn the coupling to hard or it can break. But don't worry if you do as you have a spare on the old imaging unit that you just took out. And always turn the dev unit drive in the correct direction.

Also someone had played around with the date on this copier so now it shows the image unit life counter start dates as being in 2012. Not a problem but may confuse the next tech who comes to look at it and will wonder why the image units were changed 3 years before the machine was even manufactured.