Oki OKIFAX4550 Maintenance Manual page 359

F Off-hook detectors (IC8, RL7)
These circuits detect the off-hook state of the telephone connected to the TEL1, TEL2, through
LINE terminals. IC8 uses a high detection sensitivity than of RL7. In TEL/FAX mode, the higher
sensitive IC8 is used to detect the off-hook state of the telephone while the main equipment is
hunting a line.
Usually, IC8 is short-circuited by the CML relay (7) in the standby state and RL7 is used for off-
hook detection.
Q FICC (IC4)
This circuits reduces the DC resistance to increase the loop current momentarily to assure
operation of the switch at line seizuring.
R
Constant current circuits (Q502 and Q503)
These circuits provide DC characteristics according to the TBR-21 requirement.
S
Shunt (RL9)
This circuit prevents bell resonances in the telephone sets connected in parallel during pulse
dialing and also reduces distortions of the pulse waveform.
41309401TH Rev.4
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