Oki OKIFAX4550, Maintenance Manual

Page: 361 / 592

41309401TH Rev.4
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8.2 INU 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.
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 (Q1, R506, R507, C4, R602)
These circuits provide DC characteristics according to the line requirements.
5
Impedance matching network (R544, C513, R545, R510, C502, R512, R511, C503, R513)
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 CN35).
6 Receiving sensitivity (R516, R515, R543, R519, R520, R546)
The receiving sensitivity at line hunting is determined by R519, R520, R546 depending on the
line impedance. Similarly, the MF tone receiving sensitivity at parallel pickup is determined by
R516, R515, R543, R519, R520, R546. The receiving sensitivity is set using connector keys
(CN15 to CN35).
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 (IC2)
This circuit generates pulse dial signals.
0 MUTE (IC3)
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 C7. If it
detects MF or CNG tones without seizuring a line, it opens to increase the impedance.
C Pickup RC (R505, C5)
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 of RI having 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.