Oki OKIOFFICE 84, Service Manual

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Note 1:
This procedure may be omitted depending on the dial parameters.
Note 2:
MF (Multi-frequency) tone is generated by the modem and transferred to the telephone line via the NCU
board.
3. Explanation of CN3 Terminals
CN3 pin No. Terminal name Explanation UNC
(US, CA)
1 REV2 Detection and output of the direction of DC line
current. *
2 OH2 Detection of off-book of terminal connected to
TEL-1 or TEL-2.
3 OH1 Output upon circuit current detection after fax line
seizure. *
4 RI 0 - 5 V signal output synchronized with the ringing
signal frequency.
5 NC Unused terminal. *
6 PP Relay control signal for special service code
detection at parallel pickup or remote reception
7, 8 E GNC
9, 10 sub +5 V Sub power supply for OH2 and RI detection
11, 12 + 5 V Power supply for relays and logic circuits
13, 14 + 5 V A =% V power supply for analog circuit *
15, 16 S TX Signal
17, 18 - 5 VA - 5 V power supply for analog circuit *
19, 20 R RX Signal
21, 22 SG Signal ground
23, 24 Rp Receiving sensitivity determination terminal
25 DP Pulse dial control signal
26 CML Line seizure control signal
27 F, ICC Loop current control signal upon line seizure *
28 SR Control signal for connection between LINE and
TEL terminals.
29 PBXE Control signal for connecting one of LINE terminal
to the PBXE terminal *
30 MUTE Control signal for pulse dial improvement and bell
shunt relay. *
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.