Oki OKIOFFICE 84 Service Manual page 427

27 FICC (IC6)
This circuits reduces the DC resistance to increase the loop current momentarily to assure operation of the switch at
line seizuring.
28 Constant current circuits (Q1 and Q2)
These circuits provide DC characteristics according to the French line requirement.
29 Shunt (RL5)
This circuit prevents bell resonances in the telephone sets connected in parallel during pulse dialing and also
reduces distortions of the pulse waveform.
30 Communication line terminal switches (CN26 and CN36)
Unlike other countries, pines 2 and 5 are connected to the line for the UK communication line. Set the switches to
"F" for France and "UK" for UK.
4.4 DN5 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.
2 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.
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.