at the begining we have bead carryout and light background on yellow, i thought about aged developer and changed it-didnt help (after half k prints the problem returns) i had before this problem on other colors and resolved it after drum have been changed. this time it didnt help. also having vh/vm fault (9-624) after performing dc933 (LDs judge NG). when adding new developer- all fine but after 500 prints developer goes to trash. also note the TC value felling down from 140 (after adding new material) to 0.

changed:
esv sensor
drum module
developer assy
developer material

swaped:
ros
halftone pwb
developer bias hvps
charge/preaclean hvps

cleaned every sensors
did dc301 after it vh/vm dissapered but after max setup and some prints returned

and still without any changes
any ideas?

it is on yellow
the esv was changed with new one, before i tried to swap it with other color - nothing.
even tried disconnect esv pwb at all and got extra fault-thats mean esv is good working.

without any changes

There were seven hits in SearchLite for this fault.  This one seemed the most relevant (developer expelled to waste container).

This hit came from one of David's countrymen,  a M. Balamurugan

didnt help. pob is ok. discovered that humidity rising (had 10 points by env sensor~5% rised up to 30 points) resolved the problem with background but vh/vm fail is still there.

Hi there
 
I had exactly the same symptoms and problems. And still I not sure about the solution. I've replaced like you did everything listed from you.
The "TC Value" in DC922  point to bad bias connection the value must not bellow 80. For good bias I use a spring from pen that I cut and I'm putting it between the shaft and contact plate , you can try with this.
Second and for now this fixed the problem, is try changing (with new ones) the Halftone Pwb Flat Cables.
I hope this helps.