Pioneer cx 938 a service manual
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Extracted text from pioneer cx 938 a service manual (Ocr-read)
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2 C X-938 1. CIRCUIT DESCRIPTIONS The LSI (UPD63710GC) used on this unit comprises five main blocks ; the pre-amp section, servo, signal processor, DAC and CD text decoder (not used on this model). It also equips with nine automatic adjustment functions. 1.1 PRE-AMP SECTION This section processes the pickup output signals to create the signals for the servo, demodulator and control. The pickup output signals are I-V converted by the pre- amp with the built-in photo-detector in the pickup, then added by the RF amp to obtain RF, FE, TE, TE zero cross and other signals. This pre-amp section is built in the servo LSI UPD63710GC (IC201). The following describes function of each section. Since this system has a single power supply ( +5V), the reference voltage for this LSI and pickup are set to REFO (2.5V). The REFO is obtained by passing the REFOUT from the LSI through the buffer amplifier. The REFO is output from Pin 89 of this LSI. All measurements are done using this REFO as reference. Note : During the measurement, do not try to short the REFO and GND. 1) APC Circuit (Automatic Power Control) When the laser diode is driven with constant current, the optical output has large negative temperature characteristics. Thus, the current must be controlled from the monitor diode so that the output may be constant. APC circuit is for it. The LD current is obtained by measuring the voltage between LD1 and V +5. The value of this current is about 35mA. 71 72 74 76 AGCI 77 RFO 75 78 79 80 73 91 90 93 92 C-3T FEO FE- TEO TE- 85 86 87 E 97 PD 99 PNF D 8283 84 B C A RF- EQ1 EQ2 AGCORFI ASY EFM PEAK DET. LPF BOTTOM DET. S/H D/A A/D D/A A/D 94 98TE2 LD VREG GND APN LDON EFM DEFECT FOK A3T MIRR To the following stage of the LSI Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref Vref ·····Vref(+2.5V) 97 PD 99 PN 98LD VREG GND AMP_PN (H:Nch L:Pch) LDON (H:LD MOVE L:STOP) Vref ·····Vref(+2.5V) 14 5 R102 10 R101 12 Q101 2SB1132 C102 0.1mF C103 100mF/6.3V PU UNIT R103 2.2kC105 0.33mF +5V 1k 110k 3pF 3pF 150k100k 100k 16k 1k Fig.1 : BLOCK DIAGRAM OF BUILT-IN RF AMPLIFIER Fig.2 : APC CIRCUIT
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C X-938 3 2) RF Amplifier and RFAGC Amplifier The photo-detector outputs (A +C) and (B +D) are added, amplified and equalized on this LSI and then output to the RFI terminal as the RF signal. (The eye pattern can be checked by this signal.) The RFI voltage low frequency component is : RFI = (A +B +C +D) ´3.2 RFI is used on the FOK generator circuit and RF offset adjusting circuit. R215 is an offset resistor for maintaining the bottom reference voltage of the RFI signal at 1.5 VDC. The D/A output used for the RF offset adjustment (to be described later) is entered via this resistor. After the RFI signal from Pin 77 is externally AC coupled, entered to Pin 76 again, then amplified on the RFAGC amplifier to obtain the RFO signal. The RFAGC adjustment function (to be described later) built-in the LSI is used for switching feedback gain of the RFAGC amplifier so that the RFO output may go to 1.5 ±0.3Vpp. The RFO signal is used for the EFM, DFCT, MIRR and RFAGC adjustment circuits. 3) FOK Circuit This circuit generates the signal that is used for indicating the timing of closing the focus or state of the focus close currently being played. This signal is output from Pin 4 as the FOK signal. It goes high when the focus close and in-play. The RFOK signal is generated by holding DC level of the RFI at its peak with the succeeding digital section, then comparing it at a specific threshold level. Thus, the RFOK signal goes high even if the pit is absent. It indicates that the focus close can take place on the disc mirror surface, too. This signal is also supplied to the micro computer via the low pass filter as the FOK signal and used for the protection and the RF amplifier gain switching. CN101 84 18 2583 8210k 10k 85FOK CIRCUIT A/D 4 A+C 16k B+D10k 16k 10kR215 12kC209 3pF R214 10k R207 1.8k C208 27pFR213 10k 80 79 74 75 76 77 D/A 12k 66 10kRFO AGCI RFIC207 0.22mFC206 3900pF FOK TO EFM CIRCUIT Fig.3 : RFAMP, RFAGC AND FOK CIRCUIT