Line Interface PCB
This PCB connects the modem to the telephone line. It contains the isoating transformer, a circuit to pass the line hold current and 3 relays which are basically equivalent to the gravity switch (hook switch), dial off-normal, and dial impulse contacts of a rotary dial
telephone.
The green LED is labelled 'Carrier' on the front panel. It is nothing of the sort. It simply indicates when the gravity switch relay is energised and the unit is thus conneted to the telephone line.
The telephone line cable plugs into the 7 pin header in the front middle of the board. Only 4 pins are used. 2 for the line, 2 for a relay contact to disconnect the associated telephone. This is the standard (for the time) Viewdata set wiring.
Line Interface PCB
This PCB connects the modem to the telephone line. It contains the isoating transformer, a circuit to pass the line hold current and 3 relays which are basically equivalent to the gravity switch (hook switch), dial off-normal, and dial impulse contacts of a rotary dial
telephone.
The green LED is labelled 'Carrier' on the front panel. It is nothing of the sort. It simply indicates when the gravity switch relay is energised and the unit is thus conneted to the telephone line.
The telephone line cable plugs into the 7 pin header in the front middle of the board. Only 4 pins are used. 2 for the line, 2 for a relay contact to disconnect the associated telephone. This is the standard (for the time) Viewdata set wiring.