Oki OKIPAGE 14EX Service Manual page 45

(2) Charging
Charging is actuated by the application of the DC voltage to the charge roller that is in contact with the image drum surface.
The charge roller is composed of two layers, a conductive layer and a surface protective layer, both having elasticity to secure good contact with the image drum.
When the DC voltage applied by the power supply exceeds the threshold value, charging begins. The applied voltage is proportional to the charge potential, with
offset of approximately -550V.
(3) Exposure
Light emitted by the LED head irradiates the image drum surface with a negative charge. The surface potential of the irradiated portion of the image drum drops,