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Circuit Operation:
The bell signal passes through C1 (R1)
pin 21 of IC1 detect the bell signal.
The ring signal is output from Pin 8 of IC1, and its volume is adjusted in 3 steps (H-L-OFF) by
SW3 then impressed on the ceramic sound generator, and so is generated.
R15, R16 . . . . . . . . . . . . . Bell sensitivity adjustment
Below content (inside ruled line) is information only for service correspondence.
Usually, the default setting is digit 6.
12.4. Power Circuit and Redial Back-up Circuit
Function:
This set is powered from the line. When it is an OFF-HOOK status, Tel Line
D17
Q1
R9
Pin 27 of IC1 (to become the power supply for IC1 speech network).
The voltage from the line is turned into a constant voltage by D2 and then supplied to the IC1,
reset circuit.
Through Tel Line
R1
R3
D17
R14 to become the power supply for IC1, and the
redial Back-up will be done.
12
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