Oki OKIFAX 5750 Service Manual page 929

An illustration of activities at the contact point of the image drum surface and the developing roller (arrow marks denote the direction of the electric field).
Note:
The toner supply roller and the developing roller are supplied with bias voltages required during the developing process as shown below. -500 VDC is
supplied to the toner supply roller, -265 VDC to the developing roller.