Line Monitor Circuit - Panasonic UF-585 Service Manual

Panasonic UF-585 / 595
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.
Line Monitor Signal
(from AGC Circuit)
Buzzer Clock
(from Control Panel Unit)
Buzzer Tone Switch
(from Output Port)
206
Volume
Control
Circuit
(IC13)
Level Control
Circuit
(Q17)
Line Monitor Circuit
Block Diagram
-
(IC14, 2)
+
AGD
(+2.5VDC)
Speaker
Amplifier
(Q18,19)
Speaker