Oki OKIOFFICE44 Service Manual page 294

4. Description of 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 by-
passes 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.
11 PP (RL6)
If this circuits detects MF or CNG tones without seizuring a line, it sets a proper receiving
sensitivity.
12 DP (RL3)
This circuit generates pulse dials.
If the circuit detects MF or CNG tones without seizuring a line, it opens to increase the imped-
ance.
13 Pickup RC (R5, C31)
These circuits insert a high-impedance resistor and capacitor serially to prevent the line imped-
ance from dropping by the line transformer T1.
14
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.
15 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 sepa-
rates 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.
16 Off-hook detector (IC2)
This circuit detects the off-hook state of the telephone connected to the TEL1, TEL2 through
LINE terminals.
Board Descriptions A - 52 OKIOFFICE 44 Serv. Man., P/N 59276801