Sony IT-A4000 Service Manual

| IT- A4000Dial : Tone DialPulse output of dialer IC maintains High and Q301 remains ON in tone type. If you press the dial key of thephone when the power supply is cut off, the tone signal is output from dialer IC (DTMF) output, input in thespeech network MF input and transmitted to the circuit.D922 is the protective diode to prevent inputting the irregular voltage to IC902.When the telephone is connected to a commercial use power supply:Dial : Pulse DialWhen you lift up the handset, you will hear the dial tone. If you press the dial keys of the phone S807, S808,$809, $813, $814, S815, S819, $820, S821, S825, S826 and S827 when the power supply is on, DP output signal ofASIC IC (IC802) outputs High, Low corresponding to the dial signal.Dial : Tone DialDP output signal of ASIC IC maintains Low and Q301 remains ON in tone type. DTMF signal is generated byconverting the digital signal from ASIC into the analog signal with CODEC IC (IC804). This signal is input intothe speech network MF input. .2-5. Dial : Speaker Phone CallWhen you press the speaker phone button, you will hear the dial tone. The same dial operation of the handsetcall when both the pulse dial and the tone dial are connected to a commercial use power supply, is conducted.2-6. HoldWhen you press the Hold button, IC806 and Hold output (12pin) becomes High, makes Q401, Q403 and Q420 ON,sets receiving and sending into Mute.2-7. Answering Machine2-7-1. Response message (OGM) recordingThe signal from the microphone is converted into the digital signal by CODEC IC (IC803) after being amplifieby IC501, and goes to ASIC IC (IC802).ACIC IC informs DSP.IC (C801) of this signal and returns the signal to ASIC after signal compressing procedurein DSP.This signal is recorded in DRAM.2-7-2. Ringer signal detection and circuit transmission of the response message (OGM)When you press the ANSWER button to set the answering machine, the button will light up. When the ringersignal is input from the circuit, the ringer signal reaches ringer IC and IC280 via S301 (1/2), RY301, LF301, R280and C280 to make the speaker ring.At the same time, photocoupler PH280 is driven. DSP IC (IC801) detects this output through buffer IC (IC805)ASIC IC (IC802). Relay RY301 and the circuit is closed after ringing for a fixed time.When the fixed record OGM is recorded, DSP receives the data recorded in DRAM through ASIC IC, the dataprocedure is conducted, and returns to ASIC.The digital data from ASIC is converted into the analog signal by CODEC IC (IC804).The analog signal converted by CODEC is amplified, input to the speech network IC, MF input, and transmitted=