Special Circuit On The Analog Board - Panasonic KX-FM330GR Service Manual

KX-FP320G / KX-FM330G

6.12. SPECIAL CIRCUIT ON THE ANALOG BOARD

6.12.1. CURRENT DETECTION CIRCUIT
1. Function
This circuit detects whether the circuit current is flowing or not. It is also used for CPC detection and Ext. Tel Hook detection.
2. Circuit Operation
If a circuit current of 10 mA or more flows in the IC1 coil when the unit or Ext. Tel is OFF-hook, the IC1 internal sensor detects
this current. Then, depending on the direction of the current, the IC1-5 pin or 6 pin switches to a low level. Then, Q1 or Q2 is
turns off, Q18 turns on, and the Gate Array IC4-43 pin on the digital board switches to a low level. If the line is cut off, the IC4-
43 pin switches to a high level.
6.12.2. LOW PASS FILTER
1. Function
This circuit is only incorporated into the products designed for the German market. Products for other markets are shorted by
J33. This low pass filter attenuates the 16-kHz account signal from the commutator to eliminate influence on the conversation
and communications.
2. Circuit Operation
This low pass filter is an eighth-order active filter, and the cutoff frequency is approximately 4 kHz.
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