Oki B 4100 Maintenance Manual page 453

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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 (S5-1 to 5-2)

These circuits set the impedance according to the line requirement.

S5-1: 370 ohm + 620 ohm//310 nF (UK)

S5-2: 600 ohm (F)

DC resistance switches (CN26 and CN36)

These switches set the DC resistance according to the line requirement.

This circuits reduces the DC resistance to increase the loop current momentarily to assure

operation of the switch at line seizuring.

Constant current circuits (Q1 and Q2)

These circuits provide DC characteristics according to the French line requirement.

This circuit prevents bell resonances in the telephone sets connected in parallel during pulse

dialing and also reduces distortions of the pulse waveform.

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.

40055101TH Rev.4

Troubleshooting