HP LaserJet 4v/mv Service Manual - Page 68

High Voltage Power Distribution The High Voltage Power Supply PCA applies an overlap of DC and AC voltage to the primary charging roller and the developing roller. This circuit also applies a positive or negative DC voltage to the transfer charging roller according to the instructions from the CPU on the Formatter PCA. This circuit also controls the image density by changing the primary AC voltage and the developing AC bias according to the setting of the print density dial. Refer to Figure 5-15 for High Voltage Power Supply timing information. Toner Cartridge Microswitch (SW501) Microswitch SW501, located on the High Voltage Power Supply PCA , is activated by the toner cartridge. If the toner cartridge is not installed, the switch opens and an error is issued by the Formatter causing the display panel message 14 NO TONER CART to be displayed. A toner cartridge must be installed and the front door must be closed before the printer can resume printing. Print Density Adjustment Adjusting print density affects the line width (boldness) of the print image. This is accomplished by varying the developer DC bias, which controls the amount of toner applied to the photosensitive drum. The Print Density control is accessible behind the front door. The point of the dark arrow is the most reduced density setting and the thick end of the dark arrow is the most increased density setting. The default setting is at center range. 5-6 Functional Overview