Brother FAX-270MC, Service Manual

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III – 23
Main PCB Circuit Diagram 4/4
1 Connector for the power supply PCB
1 -1: CR1, recording head on/off relay
2
3-terminal regulator which eliminates unstabilized components of the +8V source to
generate stabilized 5V source.
3 Connector for the NCU
3 -1: Power for the NCU
3 -2: Signals from the telephone
4 Analog signal selectors
4 -1: Selects either input signals from the handset or those from the MODEM.
4 -2: Selects either RL1 or RL2 signals inputted from the communications network.
4 -3: Selects either sound signals (e.g., alarm beeps, key clicks and ringer sounds) generated
by the FAX engine or signals selected by 4 -2.
5
Amplifier circuit for signals outputted from the MODEM.
6 Analog front end IC which processes the analog I/O signals from/to the MODEM.
7 Amplifier & shaper circuit for signals inputted from the communications network.
8
Telephone circuit for transmitting signals.
9 Speaker amplifier circuit which amplifies sounds issued from the above analog signal
selector
4 -3 and feeds them to the speaker.
:
Connector for the speaker
a Speaker volume control circuit
a -1: VOL1 OFF ON ON
a -2: VOL2 OFF OFF ON
Speaker volume High Medium Low (ON: Closed OFF: Opened)
1
1
-1
2
3
3
-2
3
-1
4 -1
4 -2
4
-3
5
6
7
8
9
:
a
a
-1
a -2