Samsung SCH-1500 series Service Manual

Also see for SCH-1500 series: User guide

6-4 Samsung ElectronicsCircuit Description6-1-4 Audio PartTX AUDIO PATHThe voice signal output from microphone is filteredand amplified by the internal OP-AMP and isconverted to PCM data by the CODEC (U310). Thissignal is then applied to the MSM (U100)'s internalvocoder.RX AUDIO PATHThe PCM data out from the MSM is converted toaudio signal by ADC of CODEC (U310), is thenamplified by the speaker amplifier (U330) to be sentto the speaker unit.FM TX PATHPre-Emphasis CircuitThe circuit features +6dB/oct to reduce signal lossand noise in Tx path.CompressorThe compressor features 2:1 level to reduce signalloss and noise in Tx path. The zero crossing level ofthe compressor is ±2.9 kHz/dev, attack time is 3 mS,and release time is 13.5 mS.LimiterThe limiter performs to cut ±0.53 Vp-p or higheraudio signal level so that the FM frequencydeviation is not over ±12kHz/dev. The function isused to avoid confusion over phone line. LPF isused to reduce a specific high frequency of limitedsignal.RX AUDIO PATHDe-Emphasis CircuitThis circuit is 1st LPF featuring -6dB/oct to reducesignal loss and noise in Rx path.ExpanderThe expander features 1:2 level to reduce signal lossand noise in Rx path. The zero crossing level of theexpander is ±2.9 kHz/dev, attack time is 3 mS, andrelease time is 13.5 mS.Volume AdjustVolume can be adjusted up to 6 steps for the user toobtain a proper loudness of received signal.6-1-5 TX WBD, ST, And SATThese signals are generated from MSM. Themodulation level of TX WBD and ST is±8kHz/dev, and SAT is ±2kHz/dev.6-1-6 Buzzer Driving CircuitryBuzzer generates alert tone. When the buzzerreceives the timer signal from the MSM, it generatesalert tone. The buzzer level is adjusted by the alertsignal's period generated from the MSM timer.6-1-7 Key Tone GeneratorRinger signal (pin 49) out from MSM (U100) ispassed through 2 serial LPF consisting of R341,C342, R340, and C341, amplified at the speaker amp(U330), and comes out to speaker. In hands-freemode, the key tone is applied to RX audio linethrough the LPF and C338, R335.