Oki OKIFAX 5400 Maintenance Manual page 325

UNC/WN5/FN5/DN5
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40838301TH Rev.1
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.
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.
Off-hook detectors (IC2, RL7)
These circuits detect the off-hook state of the telephone connected to the TEL1, TEL2,
through LINE terminals. IC2 uses a high detection sensitivity than of RL7. In TEL/FAX
mode, the higher sensitive IC2 is used to detect the off-hook state of the telephone
while the main equipment is hunting a line.
Usually, IC2 is short-circuited by the CML relay (7) in the standby state and RL7 is
used for off-hook detection.
Impedance switches (S4-3 to S4-4)
These circuits set the impedance according to the line requirement.
S4-3: 220 ohm + 820 ohm//115 nF
S4-4: 600 ohm
Ring impedance switches (S1-4)
These switches set the ring impedance according to the line requirement.
Ring sensitivity switch (S4-4, S4-2)
This switch sets the ring sensitivity according to the line requirement.
Telephone cascade/parallel switches (S1-1 to S1-2)
To connect the telephone connected to the TEL1 terminal and an external trephone
in parallel, set the switches to ON.
16 kHz LPF (L7, L8, C7, C507, C9)
This low-pass filter removes 16 kHz metering pulses.
Transmitter amplifier (IC501 1/2)
This transmitter buffer amplifier amplifies DTMF signals and FAX send signals.
Receiver amplifier (IC501 2/2)
This amplifier amplifies MF tones, dial tones, and FAX receive signals.
16 kHz LPF (IC502)
This active low-pass filter removes 16 kHz metering pulses.
PBXE (RL4)
This circuits connects one end of the LINE terminal to the PBXE terminal when
requested from the PBX line.
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