Oki OKIFAX 5400 Maintenance Manual page 318

4.2 WN5 circuit diagram
1
Lightning arresters (AR1, 2)
The nominal operating voltage is 500 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.
2
Loop current detector (IC4) — Optional
When a line is seizured, this circuit detects a DC loop current to notify the fact.
For detection (OH1), it outputs the low level to the nominal input current of 10 mA or
more.
3
Diode bridge (DB1)
This circuit rectifies the loop current so that the DC circuit characteristics are not
affected by a polarity change over the line.
4 DC circuits (Q3, R540, R541, C13, R9, R209, and R309)
These circuits provide DC characteristics according to the line requirements depend-
ing on the DIP SW (S3) position.
5 Impedance matching network (R523, R536, C503 ... R823, R836, C803)
This circuit matches the impedance between the line and equipment to reduce
reflection of transmitted signals.
It provides impedance (return loss) characteristics to meet the line requirement using
the connector keys (CN15 to CN45).
6
Receiving sensitivity (R537, R539...R837, R839)
The receiving sensitivity at line hunting is determined by R539 to R839 depending on
the line impedance. Similarly, the MF tone receiving sensitivity at parallel pickup is
determined by R537 to R837. The receiving sensitivity is set using connector keys
(CN15 to CN45).
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.
9
DP (IC5)
This circuit generates pulse dial signals.
0
MUTE (IC7)
During pulse dialing, this circuit closes to reduce the DC loop resistance.
A PP (RL6)
If this circuits detects MF or CNG tones without seizuring a line, it disconnects
Impedance matching Net work (5) to increase the input impedance and also sets the
receiving sensitivity.
B
MUTE (RL3)
During pulse dialing, this circuit opens to prevent pulse distortion caused by capacitor
C11. If it detects MF or CNG tones without seizuring a line, it opens to increase the
impedance.
C
Pickup RC (R590, C31)
These circuits insert a high-impedance resistor and capacitor serially to prevent the
line impedance from dropping by the line transformer T1.
40838301TH Rev.1 A3 - 37
UNC/WN5/FN5/DN5