Sharp FO-2970M Service Manual - Page 58

FO-2970MU 5) Matching transformer The matching transformer performs electrical insulation from the telephone line and impedance matching for transmitting the TEL/FAX signal. 6) Hybrid circuit The hybrid circuit performs 2-wire-to-4-wire conversion using the IC1 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. 7) 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. [Control signals from output port] Signal Name Description CML Line connecting relay and DP generating relay H: Line make L: Line break SP MUTE Speaker tone mute control signal H: Muting (Power down mode) L: Muting cancel (Normal operation) TEL MUTE Handset reception mute control signal H: Muting L: Muting cancel RCVOL Handset receiver volume control signal Volume High Middle Low (The circuit is located in the control PWB.) RCVOL H L L Set the line driver of MODEM (FM336) to - 6 dBm VOL A VOL B VOL C (The circuit is located in the control PWB.) Speaker volume control signal VRSEL1 VRSEL2 matrix VOL A VOL B VOL C RING./ Buzzer DTMF Receiving H L L High - High L H L Middle - Middle L L H Low - Low L L L - Fixed - GAIN-C Reception gain switching signal (The circuit is located L: When connected to line, 1: 1 gain in the control PWB.) H: When not connected to line, HIGH gain BZCONT Speaker output signal switching (The circuit is located H: Buzzer signal output in the control PWB.) L: When monitoring line signal MIC MUTE Handset mic mute control signal H: Muting L: Muting cancel [Signals for status recognition according to input signals] Signal Name Function RHS H: The handset is in the on-hook state. (On the HOOK-SW PWB) L: The handset is in the off-hook state. CI Incoming call (CI) detection signal. H: The handset or external telephone is in the on-hook state. HS L: The handset or external telephone is in the off-hook state. [Other signals] Signal Name TEL IN TEL OUT TXOUT RXIN Function Receiving signal from line or modem Transfer signal to line Transmission (DTMF) analog signal output from modem Reception (DTMF, others) analog signal input into modem No. Signal Name (CNLIU) No. 1 +24V 7 2 DG 8 3 +5VA 9 4 CML 10 5 CI 11 6 HS 12 Signal Name (CNLIU) RHS TXOUT RXIN TELMUTE TELOUT TELIN No. Signal Name (CNHS 1 and 2) No. Signal Name (CNHS 1 and 2) 1 RHS 2 DG 8) CI 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 PC2 through the C3 (0.82 uF), R3 (22 K), and ZD3 when the ring signal is inputted from the telephone line. 9) Power supply and bias circuits The voltages of +5VA and +24V are supplied from the control PWB unit. 5 - 22