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Extracted text from pioneer cx 958 service manual (Ocr-read)
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C X-95 8
1. CIRCUIT DESCRIPTIONS
The LSI (UPD63711GC) used on this unit comprises six main blocks ; the pre-amp section, servo, signal processor,
DAC, CD text decoder (not used on this model) and LPF. 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
UPD63711GC (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
3p
3p 150k100k 100k
16k
1k
Fig.1 : BLOCK DIAGRAM OF BUILT-IN RF AMPLIFIER
Fig.2 : APC CIRCUIT
Page 2
C X-95 8
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.
R207 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) RFOK 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 6
1383 8210k
10k
85FOK
CIRCUIT A/D
4 A+C
16k
B+D10k
16k
10kR207
12kC216 3pF
R205
10k
R206
1.8k C217
27pFR204
10k
80 79 74 75 76 77
D/A
12k
66
10kRFO AGCI RFIC215
0.1mFC213
3900pF
FOK TO EFM
CIRCUIT
Fig.3 : RFAMP, RFAGC AND FOK CIRCUIT