Sharp FACSIMILE FO-4500 Service Manual page 110

FO-4500H
3. Hook status detection circuit
The hook status detection circuit detects the Status of hook switch
(RHS) of Built-in telephone.
•
The status of on-hook switch (RHS) is determined from the
logical level of RHS signal.
RHS LOW: OFF HOOK
RHS HIGH: ON HOOK
4. Dial pulse generation circuit
The pulse dial generation circuit comprises the photo-coupler
PC2, polarity guard REC1, and transistor Q1, Q2.
The dial pulse turns on CML, controls the base current of transis-
tor Q2 by supplying the DP signal to the photo-coupler PC2, and
generates the DP signal by making the TEL circuit make and
break.
5. CML relay
The CML relay switches over connection to the matching trans-
former T1 while the FAX or built-in telephone is being used.
6. Matching transformer
The matching transformer performs electrical insulation from the
telephone line and impedance matching for transmitting the
TEL/FAX signal.
7. Hybrid circuit
The hybrid circuit performs 2-wire-to-4-wire conversion using the
IC105 and IC104 of operational amplifier, transmits the voice
transmission signal to the line, and feeds back the voice signal to
the voice reception circuit as the side tone. Also, this circuit is
operated with the analog switch IC104 as a half-duplex circuit
while the FAX is being used, and as a full-duplex circuit while the
telephone is being used.
The C11, C115, C120, C116 and C112 suppress the radio pickup
from the handset.
8. Speaker amplifier
The speaker amplifier monitors the line under the on-hook mode,
outputs the buzzer sound generated from the gate array (IC11:
control PWB), ringer sound, DTMF generated from the modem
(IC1: control PWB), and line sound.
9. Adjustment of voice volume
The voice volume can be adjusted by using the panel bottons "→"
and "←".
The reception level can be adjusted by pressing the →/← but-
•
ton when the handset is located in the off-hook state.
10. Signal selection
The following signals are used to control the transmission line of
TEL/FAX signal. For details, refer to the signal selector matrix
table. (See page 5-23)
•
TEL MUTE: Controls the mute of handset voice transmission
signal.
•
RCV MUTE: Controls the mute of handset voice reception sig-
nal.
•
SP MUTE: Controls the mute of speaker amplifier.
•
MPX B: Switches over the gain of reception amplifier.
H: Amplifier gain decreased
L: Amplifier gain increased
•
MPX A: Mutes the transmission drive amplifier.
H: Selected when the telephone is being used or
when the FAX signal is being transmitted
L: Selected when the FAX signal is being re-
ceived
11. Cl detection circuit
The CI detection circuit detects the CI signals of 15.3 Hz to 68 Hz.
A CI signal, which is provided to the photo-coupler PC1 through
the C15 (0.82 µF), R1 (22 K), R2 (13K) and ZD3 when the ring
signal is inputted from the telephone line, is filtered by the R137
and C9 and then transmitted to the control PWB through the Q110
(DTC114).
12. Power supply and bias circuits
The voltages of +12V and +5V are supplied from the control PWB
unit. The IC104 of operational amplifier generates 6V bias voltage
and supplies it to the IC104, 106, 105.
5 – 20