HP Pro 4300 C9H70UT C9H70UT#ABA manual Low-voltage circuit block diagram

The developing voltage (bias) causes the toner to adhere to the electrostatic image that the laser/scanner assembly created on the photosensitive drum. There are two types of developing biases. The developing dc negative bias and the developing ac bias. Both biases are generated by the high-voltage circuit on the power supply. These biases are superimposed on one another and then applied to the primary charging roller which will transfer the biases to the drum. The biased developing cylinder picks up toner particles and deposits them onto the electrostatic image on the photosensitive drum. The image is now visible on the drum.

The transfer voltage (bias) allows the toner image on the photosensitive drum to transfer to the media. There are two types of developing biases. The transfer dc positive bias and the dc negative bias. Both biases are generated by the high-voltage circuit on the power supply. Transfer dc positive bias is applied to the transfer roller during the toner transfer process. Transfer dc positive bias is applied to the transfer roller during the transfer roller cleaning process. The dc positive bias attracts the toner to the media (this transfers the toner image on the photosensitive drum to the media). The dc negative bias is used to clean residual toner off of the transfer roller.

The fuser voltage (bias) prevents toner on the media from sticking to the fuser’s pressure roller.

For the HP LaserJet 4200 there is one type of fuser bias. A dc positive bias is generated by the sub high-voltage circuit on the power supply. The dc positive bias is applied to the pressure roller in the fuser.

For the HP LaserJet 4300 there are two types of fuser biases. The fuser dc positive bias and a dc negative bias. Both biases are generated by the sub high-voltage circuit on the power supply. The dc positive bias is applied to the pressure roller in the fuser. The dc negative bias is applied to the fixing film in the fuser.

Low-voltage circuit

The low-voltage circuit converts the ac power from the power source (the wall receptacle the printer’s power cord is plugged into) into the direct current voltage (vdc) used by printer components (like the motors and fans). The ac voltage is converted into +24 vdc, +5 vdc, and +3.3 vdc. The +24 vdc voltage is supplied to printer components like the main motor, laser/ scanner assembly motor, solenoids and clutches. The +5 vdc voltage is supplied to the laser/ scanner assembly. The +3.3 vdc is supplied to the sensors and the DC controller PCA.

Figure 11. Low-voltage circuit block diagram

74 Theory of operation Q2431-90912