Focus Circuit - LG GSA-4163B Service Manual

2. Focus Circuit

2-1. Block Diagram
Disc
Optical
Motor unit
Pick-up
HOP-7532TS
FACT-
FACT+
FACT-
2-2. Focus Servo
The aim of Focus Servo is to maintain the distance between object lens of P/U and disc surface, so that the
detected RF signal(A, B, C, D, EF1, EF2, EF3, EF4) can be maximized.
Focus Error Signal(FE) generates from focus error detection block in RF IC(HD153724) using Conventional
Astigmatism Detection method, Differential Astigmatism Detection method.
Focus Gain and path can be changed at the RF IC(HD153724) according to the disc, and the resulting output
FE(HD153724 4pin) is input to DSP IC(HD153724 100pin).
The Focus Search operation is using FE, PE Signal, therefore check FE, PE signals when Focusing is failed.
The role of DSP IC(R8J32006FP) is Focus Digital Controller. The operation path is as follows;
FE Signal is input to DSP IC(R8J32006FP 100pin), and after A/D Conversion, Digital Equalizer Block and D/A
Conversion in R8J32006FP, the output signal FOD(R8J32006FP 116pin) is input to Drive IC(R2S30200FP
40pin).
The drive output signal FACT+/FACT- generated according FOIN(R2S30200FP 40pin), and drives focus
actuator in the P/U unit.
42
A+B+C+D
A,B,C,D
A,B,C,D
(EF1~EF4)
(A+C)-(B+D)
(A+C)-(B+D)+K[(EF1+EF3)-(EF2+EF4)]
FOD
FACT+
34
35
IC601
R2S30200FP
LPF
IC101
HD153724TF
LPF
Focusing
116
DAC
Compensator
IC301
R8J32006FP
FOIN
40
REF
42
EN1
20 CTL1
EN2
21 CTL2
HAVC
LS
G 5
to
0.8V
HAVC
LS
G 4
to
V14
ADC
C338
PE
FE
FE
R334
C325
FE
GND
100
101
PE
R346
FOD
1.65V