Samsung MAX-805 Service Manual page 23

Special Circuit Descriptions
5-2 Servo Block
5-2-1 Focus Servo Block
When defect=ÒH (the defect signal is detected), the focus servo loop is muting in case of focus phase
compensation. At this time, the focus error signal is outputted through the low pass filter formed by
connecting a capacitor(0.1µF) and a built-in 470K½ resistor to the FDFCT pin (pin60). Accordingly, the focus
error output is held as the error value just before defect error during defect occuring. The peak frequency of
focus loop phase compensation is at about 1.2KHz when the resistor connected to FSET pin(pin6) is 510k½,
and it is inversely proportional to the resistor connected to the FSET pin. While the focus search is operating,
the FS4 switch is on and then focus error signal is isolated, accordingly the focus search signal is output by
FEO pin(pin48). When the FS2 switch is on(focus on), the focus servo loop is on and the focus error signal
from FE2 pin(pin58) is outputted through the focus servo loop.
58
FE2
60
FDFCT
28
FGD
FS3
27
5-2-2 Tracking Servo Block
During detection of defect, the tracking error signal is output through the tracking servo loop after through
the low pass filter formed by connecting a capacitor(0.1µF) and a built-in 470K½ resistor to the TDFCT
pin(pin57) in case of tracking phase compensation. The value of tracking gain up/down can be controlled by
TGU and TG2 pin. The peak frequency of tracking loop phase compensation, the dynamic range and offset of
op amp can be adjusted by changing the value of resistor connected to FSET pin same as focus loop. In case
of unstable status of actuator after jumping, the ON/OFF of tracking loop is controlled by TM7 switch of
break circuit.
After 10-track jumping, servo circuit gets out of the liner range and actuator,s tracking is unstable occasionally.
Accordingly, unnecessary jumping with many tracking error should be prevented.
5-6
3.6K
60K
-
FZCI
+
20K 48K
470K
FS4B
DFCTI
46K
580K
FS3
TE2 53
470K
680K
57
TDFCT
TG1
DFCTI
110K
TGU 61
82K
TG2
62
TG2
470K
92K
Focus Phase
Compensation
40K
130K FS2B
10K
50K
40K
-
+
26 6
FLB FSET
TM4
680K
TM3
TG1
10K
66PF
TRACKING
10K
PHASE
COMPENSATION
TM7
6
FSET
VC
- FSCMPO
+
-
48
+
-
+
47
3.6K
PS
FS1
4 3
X1 0 0
X2 0 1
X3 1 0
X4 1 1
3
FRCH
49 TE-
90K
-
50
TED
+
Samsung Electronics
FED
FE-