Oki OKIOFFICE84 Maintenance Manual page 308

UNC/WN5/FN5/DN5
4.4 DN5 circuit diagram
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40672201TH Rev. 4
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.
Loop current detector (IC4) - Optional
When a line is hunt, 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.
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.
DC circuits (Q3, R540, R541, C13, R9, R209)
These circuits provide DC characteristics according to the line requirements.
Impedance matching network (R523, R536, C503, ...)
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 S4-3 and S4-4.
Receiving sensitivity (R537, R539, R637, R639)
The receiving sensitivity at line hunting is determined by R539 to R639 depending
on the line impedance. Similarly, the MF tone receiving sensitivity at parallel
pickup is determined by R537 or R637.
The receiving sensitivity is set using the DIP switches S4-5 to S4-8.
CML (RL1)
This circuit selectively switches the line between the telephone or facsimile.
SR (RL2)
This circuit connects the line with the telephone. During facsimile transmission, it
disconnects the telephone.
DP (IC5)
This circuit generates pulse dial signals.
MUTE (IC7)
During pulse dialing, this circuit closes to reduce the DC loop resistance.
PP (RL6)
If this circuits detects MF or CNG tones without seizuring a line, it disconnects NT
(5) to increase the input impedance and also sets the receiving sensitivity.
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.
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.
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