Panasonic KX-FC268RU-T Service Manual ▷ View online
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KX-FC268RU-T
b. Redundancy Compression Process Coding Mode
This unit uses one-dimensional MH format.
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KX-FC268RU-T
6.6.2.
Modem Circuit Operation
The modem (IC3) has all the hardware satisfying the CCITT standards mentioned previously.
When the ASIC IC10 (61) is brought to a low level, the modem (IC3) is chip-selected and the resistors inside IC are selected by the
select signals from ASIC (IC10) ADR0-ADR4. The commands are written through the data bus, and all the processing is controlled
by the ASIC (IC10) according to CCITT procedures. The INT signal dispatched from IRQ (pins 100 of IC3) to ASIC (IC10) when the
transmission data is accepted and the received data is demodulated, the ASIC (IC10) implements post processing. This modem
(IC3) has an automatic application equalizer.
With training signal 1 or 2 during G3 reception, it can automatically establish the optimum equalizer. The modem (IC3) operates
using the 32.256 MHz clock (X1).
When the ASIC IC10 (61) is brought to a low level, the modem (IC3) is chip-selected and the resistors inside IC are selected by the
select signals from ASIC (IC10) ADR0-ADR4. The commands are written through the data bus, and all the processing is controlled
by the ASIC (IC10) according to CCITT procedures. The INT signal dispatched from IRQ (pins 100 of IC3) to ASIC (IC10) when the
transmission data is accepted and the received data is demodulated, the ASIC (IC10) implements post processing. This modem
(IC3) has an automatic application equalizer.
With training signal 1 or 2 during G3 reception, it can automatically establish the optimum equalizer. The modem (IC3) operates
using the 32.256 MHz clock (X1).
1. Facsimile Transmission
The digital image data on the data bus is modulated in the modem (IC3), and sent from pin 56 via, amplifier IC102 and the NCU
section to the telephone line.
Refer to Check Sheet for Signal Route (P.127).
section to the telephone line.
Refer to Check Sheet for Signal Route (P.127).
2. Facsimile Reception
The analog image data which is received from the telephone line passes through the NCU section and enters pin 47 of the
modem (IC3). The signals that enter pin 47 of the modem (IC3) are demodulated in the board to digital image signals, then
placed on the data bus.
placed on the data bus.
In this case, the image signals from the telephone line are transmitted serially. Hence, they are placed on the bus in 8 bit 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 for Signal Route (P.127).
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 for Signal Route (P.127).
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KX-FC268RU-T
6.7.
NCU Section
6.7.1.
General
It is composed of bell detection circuit, pulse dial circuit, line amplifier, sidetone circuits.
6.7.2.
Bell Detection Circuit
1. Circuit Operation
The signal waveform for each point is indicated below. The signal (low level section) input to pin 10 of BBIC IC4 on the digital
board.
TEL LINE
board.
TEL LINE
→ PC101 (1, 2 → 4) → IC4 (10)
6.7.3.
On/Off Hook Circuit
Normally (ON-HOOK condition), LINE RELAY (RL101) and Opt Isorator (PC102) is OFF. While OFF-HOOK, RL101 and PC102
turns ON. This LINE RELAY is controlled by pin 83 of IC4 through the Q101. PC102 is controlled by pin 12 of IC4 through the
Q104.
ON-HOOK:
IC4 (83) Low Level
turns ON. This LINE RELAY is controlled by pin 83 of IC4 through the Q101. PC102 is controlled by pin 12 of IC4 through the
Q104.
ON-HOOK:
IC4 (83) Low Level
→ Q101 OFF → RL101 OFF
IC4 (12) Low Level
→ Q104 OFF → PC102 OFF
OFF-HOOK:
IC4 (83) High Level
IC4 (83) High Level
→ Q101 ON → RL101 ON
IC4 (12) High Level
→ Q104 ON → PC102 ON
6.7.4.
Pulse Dial Circuit
The pulse dial is generated by operating the transistor PC102 while OFF-HOOK (RL101 ON) condition.
Make state:
IC4 (12) High Level
Make state:
IC4 (12) High Level
→ Q104 ON → PC102 ON
Break state:
IC4 (12) Low Level
IC4 (12) Low Level
→ Q104 OFF → PC102 OFF
6.7.5.
Line Amplifier and Side Tone Circuit
1. Circuit Operation
The reception signal output from the line transformer T101 is input to pin (2) of IC101 via C130, R138 and then the signal is
amplified at pin (1) of IC101 and sent to the reception system at through the LPF.
amplified at pin (1) of IC101 and sent to the reception system at through the LPF.
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KX-FC268RU-T
6.7.6.
CPC (Calling Party Control) Detection Circuit
1. Function
This circuit detects the signal (cuts the current) output from the converter when the other party finishes ICM recording and
goes into the ON-HOOK status.
TAD detects this signal and disconnects the line. When the TAD is operating, pin (4) of PC105 becomes a low level.
While detecting the CPC signal, pin (4) of PC105 becomes a high level. When the CPC signal is detected, the TAD opreation
stops and the line is disconnected.
goes into the ON-HOOK status.
TAD detects this signal and disconnects the line. When the TAD is operating, pin (4) of PC105 becomes a low level.
While detecting the CPC signal, pin (4) of PC105 becomes a high level. When the CPC signal is detected, the TAD opreation
stops and the line is disconnected.
6.7.7.
Auto Disconnect Circuit
1. Function
This circuit is used to detect that the telephone connected in parallel to the same line is OFF-hook while the unit picks up the
line. If this detection circuit is activated when TAM is being delivered, the delivery stops and the circuit is automatically
released.
line. If this detection circuit is activated when TAM is being delivered, the delivery stops and the circuit is automatically
released.
2. Circuit Operation
If the line is picked up, C107 is charged by following the path shown below.
D105 (+)
D105 (+)
→ R109 → D106 → C107
When the electric potential difference between the base and emitter of Q105 becomes less than about 0.3V, Q105 and Q106
and PC103 turn off, then the IC4 pin 14 becomes a high level.
In this condition, if a telephone connected in parallel goes into OFF-hook status, the base of Q105 becomes low.
On the other hand, the emitter of Q105 goes down slowly because the capacitor (C107) is charged. Q105 turns on when the
electric potential difference between the base and emitter of Q105 becomes more than 0.6 V while being charged.
When Q105 turns on, Q106 and PC103 also turn on, then the IC4 pin 14 becomes a low level.
and PC103 turn off, then the IC4 pin 14 becomes a high level.
In this condition, if a telephone connected in parallel goes into OFF-hook status, the base of Q105 becomes low.
On the other hand, the emitter of Q105 goes down slowly because the capacitor (C107) is charged. Q105 turns on when the
electric potential difference between the base and emitter of Q105 becomes more than 0.6 V while being charged.
When Q105 turns on, Q106 and PC103 also turn on, then the IC4 pin 14 becomes a low level.
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