Ricoh FW780 Service Manual - Page 55

4.5 DEVELOPMENT BIAS 4.5.1 Basic Concept When the drum is exposed, most of the negative charge is eliminated from the areas where light strikes the drum. This leaves a negative charge pattern corresponding to the dark areas of the original. After exposure, however, a small residual charge of about --100 volts (for white paper) remains in the exposed areas. This residual charge could attract positively charged toner from the development roller, resulting in dirty background on the copy. The development bias prevents dirty background. A negative bias that is a little larger than the residual charge is applied to the development roller. This prevents the positively charged toner from being attracted to the background areas of the latent image. Bias (Volts) Manual ID Bias Manual ID Setting 4.5.2 Manual Image Density Bias The development bias is applied as shown by the above chart. In addition to the development bias, the image density is also controlled by varying the exposure light intensity. (See the exposure section.) A163 2-19 SM