Developer, what is it and what are the symptoms when it goes bad?
Developer consists of small iron particles (dual component). The developer is mixed with augers churning all the time to keep the toner mixed evenly in the developer unit. The Magnetic roller (mag roller) holds the toner and evenly distributes the toner. Think of the developer as golf balls and inside the dimples of the golf ball the toner is carried (Developer is sometimes called Carrier) and evenly distributes it onto the drum or photoconductor. When the developer material wears down the machine will dust with toner and cause backgrounding because it is unable to carry the toner as good as it did when it was new. To help confirm that you need to replace the developer, there is a yield associated with it. This yield could be 80,000 prints or 200,000 it all depends on the make and model of the equipment. This is why a good service company utilizes a service record. Then you can look to see when it was replaced last.
When changing the developer you must dump the old developer material out, vacuum and replace it with new material.
CAUTION: Some developer unit sensors are very sensitive and could pop by using a vacuum. Better to just brush out the remainder of the developer than take a chance. You must always set the toner sensor before making copies and this takes knowing the simulation codes and how to set them. It’s really not that hard you will just need the information.