HP 3500 Series

ENWW Engine control system 123
The major recipients of the +24 V, +5 V, and +3.3 V DC power are listed below.
● +24 V: motors, solenoids, clutches, high-voltage power supply PCB, memory controller PCB,
and optional parts
● +5 V: laser driver PCB, high-voltage power supply PCB, formatter, and sensors (except for the
photo interrupter)
● +3.3 V: formatter, sensor (photo interrupter), ICs inside the control panel, DC controller, and
the memory controller
Protective function
The low-voltage power supply circuit has a protective function against overcurrent and overvoltage
to prevent failure in the power supply circuit. It automatically breaks the output voltage when
overcurrent or overvoltage occurs due to an issue, such as a short at the load side.
CAUTION Turn off the power switch (SW3001) to repair the load side, then turn the power back on after the
repair is complete, since the DC voltage from the low-voltage power supply circuit may be stopped
by this function.
There are two power supply fuses (FU3001, FU3002) in the circuit which have a protective
function. The power supply fuse opens and interrupts the current when an overcurrent occurs in
the AC line.
CAUTION To recover the low-voltage power supply after it has been broken for protection, turn the power off
(by switching off or unplugging) and leave the printer off for three minutes or longer before turning
the power back on.
Safety
For the safety of users and service technicians, the +24 V is divided into two: +24 VA and +24 VB.
The +24 VA is supplied from the DC controller all the time, whereas the power supply of the +24
VB stops when the door-open detection switch (SW1) is cut off. The high-voltage power supply
circuit, motors, and solenoids are supplied with the +24 VB. They stop when the front cover is
opened. This is to protect the users and the service technicians from an electric shock or injury to
their hands.
The +24 VB also functions as a DOOR-OPEN DETECTION signal (DOPEN). The CPU judges the
door open when the +24 VB supply stops.
Sleep mode
This function saves the power consumption of the printer. It is controlled by the DC controller and
goes through the following sequence:
1 The DC controller receives a sleep command from the formatter.
2 The DC controller then sends the SLEEP signal (/REM24) to the low-voltage power supply
circuit within the specified time from receipt of such command. (“L” to “H”).
3 When /REM24 signal (“H”) is sent, the low-voltage power supply circuit stops the power supply
of 24V to each load and puts the fuser temperature control, fans, and motors into the STOP
state.
The printer returns to the WAIT period when it receives the command to release the sleep mode
from the formatter.