Oki OKIFAX OF5900, Maintenance Manual

Page: 394 / 472

UNC/WN5/FN5/DN5
OKIFAX 5700/5900 A3 - 44
4. Description on the NCU Block Diagram
4.1 UNC circuit diagram
1
Lightning arresters (AR1, 2)
The nominal operating voltage is 350 V.
When connecting the ground of the arrestor to the chassis, tighten ARG on the
PCB with a screw. At this time, the PCB is grounded through the power cable.
The TB1 arrestor ground terminal can also be used to connect to the earth
directly.
4
DC circuits (R10, R11, C4)
These circuits provide DC characteristics according to the line requirements
using the primary DC resistor in the line transformer T1 and the R10 and R11
resistors . The capacitor C4 bypasses AC signals.
5
Impedance matching network (R523, R536, C503)
This circuit matches the impedance between the line and equipment to reduce
reflection of transmitted signals.
6
Receiving sensitivity (R574, R504)
The receiving sensitivity at line seizuring is determined by R574 and the MF
tone receiving sensitivity at parallel pickup is determined by R504.
7
CML (RL1)
This circuit selectively switches the line between the telephone or facsimile.
8
SR (RL2)
This circuit connects the line with the telephone. During facsimile transmis-
sion, it disconnects the telephone.
A
PP (RL6)
If this circuits detects MF or CNG tones without seizuring a line, it sets a
proper receiving sensitivity.
B
DP (RL3)
This circuit generates pulse dials.
If the circuit detects MF or CNG tones without seizuring a line, it opens to
increase the impedance.
C
Pickup RC (R5, C31)
These circuits insert a high-impedance resistor and capacitor serially to
prevent the line impedance from dropping by the line transformer T1.
D
Ring detectors (IC1)
These circuits detect a ring signal arriving to the line. If the input ring signal
exceeds a specific voltage, the circuits output a signal having of RI the same
frequency as incoming RI.
E
Line transformer (T1)
This circuit processes send/receive signals required for facsimile transmission,
dial tone receive signals required for automatic dialing, and MF tone send and
remote receive signals. It separates between the line and equipment in terms
of DC and also keeps a balance between the line and the ground. The
transformer on the UNC board for OKIFAX 5600 is covered with the shield
case for the low-level receiving countermeasure.
F
Off-hook detector (IC2)
This circuit detects the off-hook state of the telephone connected to the TEL1,
TEL2 through LINE terminals.