Panasonic KX-FM89BX, Service Manual, Page: 205 / 276

units. Here, the internal equalizer circuit reduces the image
signals to a long-distance receiving level.
This is designed to correct the characteristics of the frequency
band centered about 3 kHz and maintain a constant receiving
sensitivity. It can be set in the service mode.
Refer to
CHECK SHEET ().
3. DTMF Transmission (Monitor tone)
The DTMF signal generated in the modem (IC505) is output from
pin 69, and is then sent to the circuit on the same route as used
for facsimile transmission.
Refer to
CHECK SHEET ().
(DTMF Monitor Tone)
Refer to
CHECK SHEET ().
4. Call Tone Transmission
This is the call signal which is generated in the ASIC (IC501) and
sent to the speaker.
Refer to
CHECK SHEET ().
5. Busy/Dial Tone Detection
The path is the same as FAX receiving. When it is detected, the
carrier detect bit of the resistor in the modem (IC505) becomes 1,
and this status is monitored by the ASIC (IC501).
6.7. DESCRIPTION OF BLOCK DIAGRAM IN ANALOG SECTION
1. Function
The analog section works as an interface between the telephone
line.
The analog gate array (IC551) on the digital board exchanges FAX
TX and RX signals between the MODEM (IC505) and the analog
section. / The control signals transmitted to the analog section are
output mainly from ASIC IC501, and the analog status is stored as
data in ASIC IC501.
2. Circuit Operation
[NCU]:Network Control Unit
The NCU comprises of the following; DC loop forming circuit to
connect with the telephone line; Switching circuit for other
interconnected telephones; Bell detection circuit; Pulse dial
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