Panasonic KX-FLM652CX, Service Manual

Page: 173 / 286

2. Circuit Operation
The caller ID signal input from TEL LINE is received by DTMF receiver (IC608).
Refer to ANALOG SECTION (P.169).
7.4.6. LINE AMPLIFIER AND SIDE TONE CIRCUIT
1. Circuit Operation
The reception signal output from the line transformer T200 is input to pin (2) of IC204 via C244, R237 and then the signal is
amplified at pin (1) of IC204 and sent to the reception system.
The transmission signal goes through C240, R238 and enters IC204-pin (6), where the signal is amplified. Then, it is output
from pin (7) of IC204 and transmitted to T200 via, C248, R245. Without a side tone circuit, the transmission signal will return
to the reception amplifier via C234, R229. When the side tone circuit is active, the signal output from IC204 pin (7) passes
through C236, R241, R233, C234, and R229 and goes into the amplifier IC204 pin (3). This circuit is used to cancel the
transmission return signal.
The TX signal is output to the circuit analog the route from the IC204 7 pin
→
C248
→
R245
→
T200
→
TEL LINE.
However, if balance is lost in the bridge, a voltage occurs between the IC204 2 pin and 3 pin and a side tone results, because
the balance cannot be maintained completely at all frequencies in the audio range some side tone always occur.
7.4.7. REMOTE FAX ACTIVATION CIRCUIT
1. Function
Another telephone connected to same line activates the unit to the FAX mode by using a DTMF signal.
2. Signal Path
Refer to CHECK SHEET (P.136).
7.4.8. TAM INTERFACE CIRCUIT
This circuit is to switch between FAX receiving and the external TAM’s message recording automatically. This circuit consists of an
EXT.TAM OFF-HOOK detect circuit, transformer, amplifier, Analog ASIC and MODEM.
For details, please refer to TAM INTERFACE SECTION (P.174).
7.5. ITS (Integrated telephone System) and MONITOR SECTION
7.5.1. GENERAL
The general ITS operation is performed by the special IC209 which has a handset circuit. The alarm tone, the key tone, and
the beep are output from the ASIC IC604 (digital board).
7.5.1.1. TELEPHONE MONITOR
1. Function
This is the function when you are not holding the handset and can hear the caller’s voice from the line.
2. Circuit Operation
(Telephone Monitor Signal Path)
Signals received from the telephone line are output through at the speaker via the following path.
3. Signal Path
Refer to CHECK SHEET.
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