HP LaserJet 1100 Service Manual - Page 43

Power system on ECU The AC, DC, and high-voltage power supply circuits are all contained within the ECU. AC power distribution The AC power circuitry supplies AC voltage whenever the power cord is connected to the AC power source. AC voltage is distributed to the DC power supply circuitry and to the AC driver circuitry, which controls AC voltage to the fusing assembly's heating element. DC power distribution The DC power distribution circuitry, located on the ECU, distributes +3.3 V DC, +5 V DC and +24 V DC as follows: Table 3-1. DC power distribution +3.3 V DC Formatter Laser/Beam Detect Circuitry ECU +5 V DC: Formatter Photosensors ECU Laser/Beam Detect Circuitry +24 V DC: Motor Laser Scanner Motor Document Scanner Motor Solenoid Formatter +24VA DC: High Voltage Power Supply Overcurrent/overvoltage There are two overvoltage devices in this printer: • Fuse F101 provides overcurrent protection for the fusing system circuitry. To check or replace the fuse requires the removal of the ECU. Fuse F102 (found only on 110V units) provides overcurrent protection to the printer DC power supply circuitry. • In addition, the +24V DC, +3.3 V DC, and +5V DC power circuitry contains an overcurrent protection circuit which automatically shuts off the output voltage when an overcurrent condition occurs due to a short or abnormal voltage on the load side. 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 roller according to the instructions from the ECU. 46 Functional Overview C4224-90962