Positron Teleline 751221, Description And Installation

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Standalone Telephone Unit 7
751221
Main Isolator Bias Circuit
The Main Isolator Bias Circuit generates the off-hook and ring trip signals, and
feeds a -24 V dc (on-hook potential) bias to the Station side telephones.
Power Supply PCB
The Power Supply PCB accepts either 120 V ac or -24 to 130V dc, and provides
-24 V dc to the Station side circuitry. It also keeps the onboard battery backup
charged.
Fuse F1 and F2
Fuse F1 limits the power supply’s input current in case of input power
overvoltage or power supply circuit failure. Fuse F2 protects the power supply
circuitry if the battery is reversed when connected. For the location of F2, refer to
Figure 2.