LG RH1777, Service Manual

Page: 96 / 110

4-34
DESCRIPTION OF CIRCUIT
1. ALPC (AUTOMATIC LASER POWER CONTROL) CIRCUIT
1-1. BLOCK DIAGRAM
1-2. ALPC (AUTOMATIC LASER POWER CONTROL) CIRCUIT OPERATION
THE ALPC BLOCK DETECTS THE LASER OUTPUT POWER OF THE FRONT MONITOR. THE POWER SIG-
NAL DETECTED WITH THE PD FOR FRONT MONITOR
DETECTION IS INPUT THE VOLTAGE FROM THE VPD PIN(123PIN) OR THE FPDM PIN(127PIN), THE REF-
ERENCE SIGNAL OF THE INPUT SIGNAL IS
INPUT FROM THE VREFPD PIN(124PIN). THE ALPC BLOCK GENERATES THE SINGALS FROM THE INPUT
LASER POWER SIGNALS IN THE
FOLLOWING DETECTION SYSTEMS. THIS BLOCK HAS FOUR DETECTION PATHS:ALL AVERAGE VALUE
PATH, MULTI PULSE AVERAGE/PEAK VALUE
DETECTION PATH, ERASE/BOTTOM VALUE DETECTION PATH, SPACE/PLAYBACK POWER VALUE
DETECTION PATH.
MN103SA6G
Write
Strategy
LIC 201
LPM 101
Optical
Pick-up
LPC-812R
LD PD
LDD
Serial
I/F
D/A
D/A
D/A
D/A
D/A
D/A
M
P
X
LIC 121
AN22113A
APC
19
A/D
ADSC
S/H
Signal
FM 123
VPD
127 FPDM
124
VREFPD
40 41 42
SH1 SH2 SH3
VGA
LPF
Ave
Erase
Space
VGA
S/H2
S/H3
S/H1