Samsung MAX-870, Service Manual

Page: 23 / 92

Special Circuit Descriptions
5-4 Samsung Electronics
5-1-7 Defect Circuit
5-1-8 APC Circuit
The RFO signal bottom, after being inverted, is held with two time constant of long and short.
The short time-constant bottom hold is done for a disc mirror defect more than 0.1msec, the long
time-constant bottom hold is done with the mirror level prior to the defect. By differentiating this with a
capacitor coupling and shifting the level, both signals are compared to generate the mirror defect detection
signal.
As the laser diode has large negative temperature characteristic in its optical output when driven with a
constant current on laser diode. Therefore, the output on processing monitor photo diode, must be a
controlled current for getting regularly output power, thus the APC (Auto Power Control) circuit is composed.
75K
43K
28K
75K
VC
37.5K
75
2
5 4
41
RFO
DCB
SSTOP/DFCT
DFCT
DCC2 DCC1
+
-
+
-
BOTTOM
HOLD
BOTTOM
HOLD
43.5K LD
5.15K
150K
150K
150K
300K
0.75K
69
70
PD
LDON
PN
From Micom
+
-
+
-