2804 on a C6501

[jrf]

Hello all
We are getting a 2804 code
I have replaced the black dev unit, hv1 and 2 and IDC sensors and charge corona.
Test print for black is very weak or totally blank.

Colour registration will set up but always fails on gamma

Any ideas please.

[seniortech]

I have seen this problem many times with very poor black density or black coming out grey, it is impossible to run gamma adjustments as the patches on the transfer belt will be grey, not black and the test will therefore fail.

In service mode go to Process Adjust/Drum Peculiarity Adjust and recall factory settings. you should then find that your black test prints are black, not grey. You will have to do your color registration and gamma adjustments again after.

Best of luck

[jrf]

Thanks for this info seniortech,

It certainly helped

[dljorg]

I too have seen this 2804 code multiple times and the fix you mention (reset to standard data) works well.

Question is why is this happening?

Using the Sensor Output Check you generally find that the black channel drum potential Vo and Vi is out of range. If I understand the system it gets that way because the Max Density sensor looks at at target on the transfer belt and changes the drum charge to make the target what it thinks is correct.

Possible a dirty potential sensor can do this but you can check for a dirty sensor in sensor output check, potential sensor readings at rest should be -002 or so, dirty the number gets way bigger 50 to 60. I have seen dirty sensors cause 2804 codes but not all the time. Generally swapping sensors (and sensor circuit boards) between channels then using sensor output check for surface potential shows that the sensor is OK.

Possible the machine got a bit undertoned and did not call for a new bottle (frequently in these situations you will find the black toner bottle empty - but not all the time). Forcing the machine to tone up (again in sensor output check) can fix that. You still need the reset to standard data to get the machine back to running normally.

Possible that the color reg sensor (that's where the max density sensor lives) is flaky but I have replaced that only to have the problem come back. You can also not replace it and do the reset to standard data and the machine goes on to work fine.

I have replaced the HV1 charge supply (nasty job) but never got a sure fix from that.

If you run test pattern 62, 8 copies, and can see that black is a problem then the black dev unit becomes suspect. Dump the black developer and or replace the developer unit. That has fixed a couple but not all the time.

Of course a machine way overdue for a PM or if the counters at PM time were not correctly reset can be a potential reason but again not all the time.

Have I missed an possible reasons for 2804?

Seniortech in this string has the fix, just wish I knew an ounce of prevention if one exists.