Oki B 4100 Maintenance Manual page 449

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 depending 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 deter-
mined 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 discon-
nects 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.
40055101TH Rev.4
449 /