Oki OKIFAX 5400 Maintenance Manual page 316

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 transmission, 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 5400 is covered with the shield case for the low-level receiving counter-
measure.
F Off-hook detector (IC2)
This circuit detects the off-hook state of the telephone connected to the TEL1, TEL2
through LINE terminals.
40838301TH Rev.1 A3 - 35
UNC/WN5/FN5/DN5