Oki OF5600, Service Manual

Page: 333 / 448

Board Descriptions A - 49 OF 5300/5600 Serv Man, P/N 59278301
5. General functional description
5-1 General
The power supply unit consists mainly of AC transformer and a power PCB (1VP board
for AC120V/2VP board for AC230V). A block diagram of the power supply unit is shown
in Figure A3.6.1 The power PCB is composed of five main circuits: AC input section,
heater control section, low-voltage section, high-voltage section and protection circuit.
The low-voltage section provides a +5V output by a DC-DC converter and other output
voltages (+30V, +8V and -8V) simply by rectifying and smoothing the respective outputs
of the AC transformer. The high-voltage section (TR1, TR2, DB1, DB2, SB1, SB2, CB
and CH) produces a flyback voltage from 5V by using a drum coil and a high-voltage
transformer.
5-2 Circuit description
5-2-1 AC input section
1) AC commercial power is supplied to line filter circuit through the AC inlet, power
switch (SW1) and the fuse (F1). Fuse F1 is used for protecting the heater circuit.
2) The filter circuit consists of L101,R1, C1, C2, C3 and L1. Capacitors C1 and C2 are
not mounted in the power unit for 120VAC input.
3) Fuse F2 is used for protection for the double voltage input in the power supply unit
for 120VAC input and will not blow by shorting or opening the secondary circuit.
This fuse F2 is not mounted in the power supply unit for 230VAC input.
5-2-2 Heater control circuit
1) The AC power divided from the AC input section passes through L2 for noise
elimination and is fed to the heater via D1 (operating as a switch) from the power
PCB.
2) The on/off operation of D1 is controlled by the operation of photocoupler PC1
whose operation is controlled by the HEAT-N signal applied to CN3-B7 pin from the
control PCB (M17 board).
3) Resistors R2 and R3 connected on the AC side of PC1 are fuse resistors to protect
themselves from firing when PC1 turns on in the event of D1 open failure.