Oki OKIOFFICE84 Maintenance Manual page 303

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.
F Off-hook detectors (IC2, RL7)
These circuits detect the off-hook state of the telephone connected to the TEL1,
TEL2, through LINE terminal. 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.
G
Impedance switches (CN15 to CN45)
These circuits set the impedance according to the line requirement.
220: 220 ohm + 820 ohm//115 nF (CN15)
275: 275 ohm + 850 ohm//150 nF (CN25)
370: 370 ohm + 620 ohm//310 nF (CN35)
600: 600 ohm (CN35)
H
DC resistance switch (SW3)
This switch sets the DC resistance according to the line requirement.
I
Ring impedance switches (S1-3 to S1-6)
These switches set the ring impedance according to the line requirement.
J Ring sensitivity switch (S4)
This switch sets the ring sensitivity according to the line requirement.
K Telephone cascade/parallel switches (S1-1 to S1-2)
To connect the telephone connected to the TEL1 terminal and an external tele-
phone in parallel, set the switches to ON.
A3 - 33
UNC/WN5/FN5/DN5
40672201TH Rev. 4