Toner Sensor; Drum Unit; Photosensitive Drum; Primary Charger - Brother HL 1240 - B/W Laser Printer Service Manual

2.3.2

Toner sensor

Detects if there is toner in the toner cartridge. The toner sensor at the left side emits light
through the window on the left side of the toner cartridge, then the toner sensor at the right
side receives it when the toner is low. They also detect whether or not the drum unit is
installed. (The toner cartridge is installed in the drum unit.)
Toner sensor
(light emission)
2.4

Drum Unit

2.4.1

Photosensitive drum

Generates the latent electrostatic image and develops the image on the drum surface.
2.4.2

Primary charger

Forms a uniform charge on the drum surface.
(1) Corona wire
Generates the ion charge on the drum.
(2) Grid
Spreads the ion charge evenly over the drum surface.
2.4.3

Transfer roller

Transfers the toner image to the paper from the drum surface.
2.4.4

Cleaner

Removes the paper dust or dirt on the surface of the photosensitive drum.
2.5

Toner Cartridge

Develops the electrostatic latent image on the photosensitive drum with toner and forms the
visible image.
Fig. 3-27
3-21
CHAPTER 3 THEORY OF OPERATION
Toner sensor
(light reception)