Read Panasonic KX-FP300E Service Manual Simplified online
12
(Model KX-FP300E)
KX-FP300E
6.8. SPECIAL CIRCUIT ON THE ANALOG BOARD (Change from original page 158.)
6.8.2. HANDSET ALC (Auto level control) DETECTION
1. Function
In some cases, it is a standard requirement that the sound level of the handset should be low when the circuit current
is large (small line loss) and high when the circuit current is small (large line loss). This circuit detects whether the circuit
current is large or small. Changes in the level are performed by the electronic volume in the analog G/A IC5.
2. Circuit Operation
The circuit current flows to R51 when in OFF-hook states. If the current at both ends of R51 exceeds approximately
1V, Q9 turns on and PC7 also turns on. As a result, the comparator IC14-6 pin switches to a low level, and the
IC14-7 pin and IC5-6 pin switch to a high level.
In some cases, it is a standard requirement that the sound level of the handset should be low when the circuit current
is large (small line loss) and high when the circuit current is small (large line loss). This circuit detects whether the circuit
current is large or small. Changes in the level are performed by the electronic volume in the analog G/A IC5.
2. Circuit Operation
The circuit current flows to R51 when in OFF-hook states. If the current at both ends of R51 exceeds approximately
1V, Q9 turns on and PC7 also turns on. As a result, the comparator IC14-6 pin switches to a low level, and the
IC14-7 pin and IC5-6 pin switch to a high level.
Circuit Diagram
+ ~
~
_
IC5
R76
R38
C24
PC7
R36
R42
C32
R50
R51
+
_
C25
Q10
R46
R43
C29
R17
+
_
_
Q3
D6
Q9
R45
6
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