Oki OKIFAX 5750 Service Manual page 884

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. The transformer
on the UNC board for OKIFAX 5600/5900/5950 is covered with the shield case for the low-level receiving countermeasure.
F Off-hook detector (IC2)
This circuit detects the off-hook state of the telephone connected to the TEL1, TEL2 through LINE terminals.