Xerox 700 faded black print

2 days ago this machine started printing a very faded black (maybe 20%).
Have replaced the drum with no difference.
Replaced both black toner cartridges and no difference.
Put in a new black developer housing, with developer, and it printed 100% black.
Now, it has started printing the 20% black again. I took out the developer housing and put into another machine and it prints 20% black on there as well.
I think the developer housing has run out of developer or something - it's brand new. I don't have any more developer here.

Has anyone else had this problem and maybe a suggestion to fix the problem please ?

 

I found the following on another website ...

"Biggest flaw is with the toner delivery system/developer housings. Here's the issue in a nutshell: toner is what the little metal developer balls in the housing use for lubricant, and if you run too much heavy coverage, the developer housings will require a constant stream of toner from the toner cartridges to stay lubricated and deliver toner to the sheet. The toner cartridges have a little tiny door that opens and dispenses toner to the developer housings, so when the housings need lots of toner due to heavy coverage, they have a hard time getting enough through the little tiny door and have to continue to make repeated requests for toner. Each one of these requests works the developer housing gears hard and the toner delivery motors hard, wearing them out much more quickly than they should, and they still don't wind up getting enough toner, wearing out the coating on the metal developer balls, necessitating the replacement of the housings."

Wondering if there is a patch or something to fix this problem?

 

When putting in a new dev unit it does keep coming up with an error 092-317 ... changing the NVM 762-315 from 3 to 0 does clear the error.

This error comes up for maybe the first 200 or 300 sheets .. after that it seems to not happen anymore.

Changing the toner cartridges or drum doesn't produce any result. Seems to be around the developer housing unit

 

Replacing the K Dev bias board should solve the problem.
Have replaced just about everything else besides the dispensing motor, which I don't think it is.

 

I would clean the laser ros from black, black toner dust on a glass