Circuit Descriptions - Pioneer CDX-MG6056ZH Service Manual

2. CIRCUIT DESCRIPTIONS

2.1 Preamplifier (UPC2572GS: IC101)
The preamplifier processes pickup output signals to
generate signals to be sent to the servo, demodulator,
and controller. The preamplifier with built-in photode-
tector converts signals from the pickup into intermedi-
ate voltage in the pickup. Then, addition is made in the
RF amplifier (IC101) to obtain RF, FE, TE, and TE zero
cross signals. The system consists of the UPC2572GS
and other components explained below. The system
uses a single power source (+5 V). Therefore, the refer-
ence voltage of IC101 and the reference voltage of the
power unit and servo circuit are REFOUT (+2.5 V). REFO
UT is obtained from REFOUT of servo LSI (IC201:
UPD63702GF) via a buffer, and is output from Pin 19 of
IC101. This REFOUT is used as reference for all mea-
surements.
Note:Do NOT short-circuit REFOUT and GND during
measurement.
1) Automatic Power Control (APC) circuit
Laser diode has negative temperature characteristics
with great optical output when the diode is driven with
constant current. Therefore, current must be controlled
by a monitor diode to ensure constant output. Thus
functions the APC circuit. LD current can be obtained by
measuring the voltage between LD1 and GND. The cur-
rent value is approximately 35 mA.
Voltage between LD1 and GND(mv)
LD current(mA) =
10 Ω + 12 Ω
EFM-IN
1
RF
envelope
AGC-OUT
2 AGC
C AGC 3
Detection
RF-IN
4
RF-OUT
5
DEFECT circuit
RF- 6
C1.3T
7
C2.3T
8
Vcc 9
Bottom
A
10
C
11
3T detection
B FE BAL
12
Control
D 13
F
14
Control
E
15
PD
16
Vcc
LD
17
APC
LDON
18
VREF-OUT
19
Fig. 1 Block Diagram of UPC2572GS
Pickup unit
Vcc (5V)
R112
Vr
2.2kΩ
5
LD MD
15
Q101
2SD1664
C124
0.1µF
C101
(100µF/6.3V)
LD1
R101
10Ω
R102
5V
12Ω
CONT
Q102 UMD2N
Fig. 2 APC Circuit
CX-890
FE
EFM comparator
FE-BAL
38
BAL
HPF
TE 37 TE-BAL
BAL
36 ASY
X12
Vcc
EFM-OUT
35
34 C.DEF
Peak
33 DEFECT
Bottom
DC shift
RFOK
32
31 MIRR
Peak
Mirror circuit
120kΩ
30 3T-OUT
C.FE
DC shift 29
28 FE-OUT
Phase detection X3
27 FE-
26 GND
TE-
25
FE BAL
24 TE-OUT1
TE-OUT2
23
X2
DET-IN
22
21 DET-OUT
VREF-IN
20
UPC2572GS
2.5V
16kΩ
PD
16
150kΩ
1kΩ
C104
1kΩ
0.33µF
17
LD
5V
18
5V
3