HP Color LaserJet MFP E78323 - Developer Units

[CHRISD2]

Hello, I have had issues with deveoper units failing after 50% usage.  2 x HP Color LaserJet MFP E78323 machines, cyan and Magenta on each.  The latest machine has printed around 150k pages. Is there a way to get them working again, is this a known issue.  When printing these colours do not print.  Toner is full, Drums have been changed.  Seeems its the deloper units again.  Can anyone give me some advice on this. Its funy that its the same 2 colours as the last machine, Cyan and Magenta, is there a known issue ?? There are no error codes or anything on the printer -  Many thanks, Chris.

[Samrit26]

Hello,

Chris, before I walk you through any structured troubleshooting, I need a bit more detail so I fully understand the failure pattern. The E78323 series can have developer-unit degradation issues depending on environment, duty cycle, and toner type, but I don’t want to assume it’s the same root cause without confirming a few specifics.

Can you clarify the following for me:

1. Print quality symptoms

   • On Cyan and Magenta, do you see completely missing planes, or is it faded/banded?

   • Does an internal Color Calibration Page show the same missing CM plane sections?

2. Supplies used

   • Are you using HP original W907-series toner and original drums/dev units, or are any reman/3rd-party parts involved?

   • Were the developer units replaced recently, or are these the original ones that failed around 50% life?

3. Environment & duty cycle

   • What is the average monthly print volume on this device?

   • Are these mostly heavy color coverage jobs (e.g., solid fills), or mixed office prints?

4. Service diagnostics

   • When you go into Diagnostics → Print Quality → CMYK Test Patterns, do Cyan and Magenta still fail?

   • Does the Developer/ETB (transfer belt) test pattern show any contamination or missing developer?

5. History

   • When the previous machine failed on Cyan and Magenta, did HP replace the developer drive assembly or only the developer units?

This model doesn't usually have a widespread, documented failure on just C/M developer units, so when you see the same 2 colors repeatedly, it often points to:

• Developer drive torque issues,

• Humidity-related developer collapse, or

• Supply consistency problems.

But I need the details above to narrow it down properly.

Once you provide that, I’ll guide you through the right next steps and determine if you’re looking at a mechanical failure requiring a depot repair.