Oki OKIOFFICE 84 Service Manual page 425

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.
17 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)
18 DC resistance switch (SW3)
This switch sets the DC resistance according to the line requirement.
19 Ring impedance switches (S1-3 to S1-6)
These switches set the ring impedance according to the line requirement.
20 Ring sensitivity switch (S4)
This switch sets the ring sensitivity according to the line requirement.
21 Telephone cascade/parallel switches (S1-1 to S1-2)
To connect the telephone connected to the TEL1 terminal and an external telephone in parallel, set the switches to
ON.
4.3 FN5 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