Line Monitor Circuit - Panasonic UF-585 Service Manual

6.2.6

Line Monitor Circuit

The Line Monitor Circuit consists of an operational amplifier (IC14, 2), analog switch (IC13), speaker amplifier (Q18, 19) and its
peripheral circuits. Its function is to monitor the dial tone, DTMF tone, response signals, etc. over the speaker. It also sounds the
output of the key touch tones, alarm tones, etc. from the panel CPU over the speaker. The received signal from the LCU PCB
passese through an AGC circuit (IC14, 1, Q7, Q6) and is then input to the analog switch for volume control. It passes through the
operational amplifier (IC14, 2) and is then input to the speaker amplifier (Q18, 19), where it is amplified to a level sufficient to drive
the speaker. The volume can be set in 9 steps (including OFF) from the panel.
Key touch tone, etc. from the panel are mixed by the operational amplifier (IC14, 2) and input to the speaker amplifier. The key
touch tones and alarm tones can be set to one of three levels, High, Low, or Off, with analog switch Q17.
Volume
Line Monitor Signal
Control
-
(from AGC Circuit)
Circuit Speaker
Amplifier
(IC14, 2)
(IC13)
(Q18,19)
+
Buzzer Clock
Speaker
(from Control Panel Unit)
AGD
(+2.5VDC)
Level Control
Buzzer Tone Switch
Circuit
(from Output Port)
(Q17)
Line Monitor Circuit
Block Diagram
200