Toshiba DP120F, Service Manual

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DP120F/DP125F Circuit Description 7-88 March 2000 © TOSHIBA TEC
The line monitor circuit consists of the CML relay (US/CA/TW: RLY2, EU/AU/ASIA/HK: RLY3),
analog switch (US/CA/TW: IC51, EU/AU/ASIA/HK: IC3), the I/OP-1 GA (IC7) and analog switches
(IC8, IC14) on the Main PBA, and other peripheral devices. It switches the telephone line path
with the analog switch and monitors the line status, ringer signal, and tone signal in facsimile
transmission and reception with the speaker connected to CN5 on the Main PBA. It also switches
the analog switch to output a buzzer tone from the speaker.
The signal to be monitored is selected by switching the analog switch (IC8) according to the
MONISEL signal, TONESEL signal, and RING/TONE signal which are output from the I/OP-1
GA.
To monitor the line during transmission and reception, the I/OP-1 GA causes the CML1 signal
to be HIGH to switch the analog switch and connect the line to the MODEM side.
For line path switching control, refer to "4. 1 Line Path Switching Control Circuit" in this chapter.
The correspondence between the respective signal levels and monitoring signals is shown in
the table below.
The monitoring signal selected by IC8 is input to the analog switch (IC14) to select an output
sound volume. The sound volume is selected by switching IC14 according to the SPVOL0-2
signals output from the I/OP-1 GA and selecting an input resistance for the monitoring signal.
The correspondence between the respective signals and sound volumes is shown in the table
below.
Monitoring signal MONISEL TONESEL RING/TONE
LINE Monitor Line 1 HIGH HIGH -
Line 2 LOW HIGH -
Ringer - LOW HIGH
Alarm/Key touch Tone - LOW LOW
Sound volume SPVOL2 SPVOL1 SPVOL0
Silent (0) LOW LOW LOW
Min. (1) LOW LOW HIGH
(2) LOW HIGH LOW
(3) LOW HIGH HIGH
(4) HIGH LOW LOW
(5) HIGH LOW HIGH
(6) HIGH HIGH LOW
Max. (7) HIGH HIGH HIGH