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 around 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 the NCU section to the telephone line the same as
facsimile transmission signals.
(DTMF Monitor Tone)
Refer to CHECK SHEET ().
4. 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 ASIC (IC501).
7.8. ANALOG SECTION
1. Function
The analog section serves as an interface between the telephone
line. The digital board (IC505) for transmission and reception of
FAX signals, switches between the digital board (IC505) and other
sections by means of a multiplexer in the NCU section.The control
signals to the individual analog sections are output mainly from
ASIC IC501, and the status information for the various sections is
also held in ASIC IC501.
Simple explanations for the various sections are given below.
2. Circuit Operation
[NCU Section]
This is the interface between the telephone line and external telephone. This is composed of a
bell detection circuit, pulse dial generation circuit, EXT. TAM OFF-HOOK detect circuit, vox
circuit, amplifier circuit for line transmission and reception, sidetonecircuit, etc.
[Modem (IC505)]
This is used for FAX signal tone modulation, DTMF signal transmission. The DTMF signal is
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