Pioneer AVIC-HD3, Service Manual

Page: 291 / 317

2
1
2 3 4
1 2
3 4
CX-3016
F
E
D
C
B
A
1.1.1 APC circuit
The light output of laser diodes (LD) has largely negative thermal characteristics. If they are driven with a constant
current, the laser power level will not be constant. The APC circuit is designed to control the current so that the laser
power becomes constant through the monitor diode (MD). The IC AN8703FH contains two APC circuits, one for DVDs
and the other for CDs. The LD current values for DVDs can be calculated by dividing the voltage between the DVDLD1
(or CDLD1 for CDs) and 5V line by 15.6 ohms (3.9 ohms x 4): approximately 26mA and 44mA for DVDs and CDs
respectively.
180mV
LPC01
LPC1
AN8703FH
For DVD
PU UNIT
2
1
+
+
+5V
DVDLD0
DVDLD1
26
DVD
LD
+5V
MD
65LD
65MD
7
3.9
Ω
3.9
Ω
3.9
Ω
3.9
Ω
–
+
170mV
LPC02
LPC2
For CD
4
3
+
+5V
CDLD0
CDLD1
24
CD
LD
78LD
CN1101
78MD
5
3.9
Ω
3.9
Ω
3.9
Ω
3.9
Ω
–
+
1.Circuit descriptions
1.1 Front-end processor (FEP) section (AN8703FH: IC1101)
The IC1101 generates servo signals for focus and tracking operations, processes the RF signal, and controls the laser
power of the pickup.
For servo signal processing, the IC contains a focus operational amplifier, a focus balance adjustment circuit, a three-
beam tracking operational amplifier, a phase-difference tracking detection circuit, a tracking balance adjustment circuit,
and an envelope detection circuit.
For the RF signal processing, the AGC and equalizer functions are contained in the IC.