has been happening to me with my 2 6250 Phaser printers. All good except black as grey.
Have tried everything and no one has an answer. Very weird !
I think it may be a new driver instead of tghe olfer ones that were made for it.
Please report here if you get it working black and how.
forget that last post - gone back to printing grey (faded black)
sorted - changed toner to a different one and works fine - grey prints now gone.
Being trying all the suggested solutions to sort this problem but with no luck. I'm hoping someone can help.
I've tried adjusting the BTR and the Fusing Unit.
the 1st is what its printing now, the 2nd is what it use to print like not prefect but better.