Special Circuit Descriptions; Cd; Rf Amp; Focus Error Amp - Samsung MAX-460V Service Manual

5. Special Circuit Descriptions

5-1 CD

5-1-1 RF Amp (KA9220) : NIC9220
58K
75
B
PD1
A C RF I-V AMP(1)
58K
PD2
D
74
Photo Detector
RF I-V AMP(2)
5-1-2 FOCUS ERROR Amp(KA9220) : NIC9220
R1
V1 32K
-(B+D)
-(A+C)
32K
164K
C2 25P
63
FE Bias
Vcc
20K
5-1-3 FOCUS SERVO SYSTEM (KA9220) : NIC9220
When FS3 is ON, high frequency gain decreases (time constant set by pin17, pin19 ; capacitor is connected
to internal resistance).
The capacitor between pin 18 and GND sets the time constant to pass the low frequencies in PLAY mode.
FE1
20K
0.1UF
The maximum frequency of the focus phase compensation is inversely proportional to the resistance connected to
pin 7. Focus search peak is about 1.1 Vp-p, and is inversely proportional to the resistance connected to pins 22,23
(if this resistance changes, the peak of track jump and sled kick change).
The inverted input of FZC comparator is set to 5.7% of the difference between Vcc and VC(pin69) {{5.7% x (Vcc-Vc)}.
Note : If the resistance connected to pin7 changes, the phase compensation peak of the focus tracking sled
servos change. (The 'op-amp' dynamic range and offset voltage also change.)
Samsung Electronics
RF SUMMING
R1
V1 AMP
10K
RFO
66
R3
10K
67
R2 V2
RF
FOCUS ERROR Amp amplifies the difference
R2
174K
between RF I-V Amp(1) output (A+C) and RF I-V Amp(2)
C1 25P
output(B+D).
These two signals are supplied to (-) and (+) input terminals of
FE
FOCUS ERROR Amp. The FOCUS ERROR output is applied to
57
FE (Terminal No.57).
FOCUS
ERROR
The FE output voltage of this low frequency component varies
AMP
according to {(A+C) - (B+D)}.
VFE is calculated as follows :
V
GND
This FOCUS ERROR voltage is sent to FOCUS SERVO .
3.6K
60K
FE2
58
20K
0.0022
470K
FS4
60
DFCT
FDFCT
62
HFGD
0.1UF
46K
EFR
61
580K
RF I-V Amp(1) and RF I-V Amp(2) currents are converted to voltage via
internal resistance of 58k½ from the current of PD1(A+C) and PD2(B+D):
These voltage are added by the RF summing amplifier.
The signal (A+B+C+D) is applied to RFO (No. 2 terminal).
RF output voltage is calculated as follows :
V = -R3 x (iPD1 + iPD2)
RF
V = -R3 x (V /R + V
RF 1 1
V V
V = -R3 x ( +
1 2
RF
10K 10K
R3
V = - x (V + V )
RF 1 2
10K
= (R2/R1) x (V2-V1) = 5.4(V2-V1)
FE
FZC
48K 92K
PHASE
COMPENSATION
40K
130K
FS2
10K
470K
FS3
40K
FSW PFSET
27
6
0.1UF
/R )
2 2
)
FSEO
48
FOCUS
120K
COIL
47
FCE
5.5U 11U
ISET
50K
20
180K
21
FS1
VREG
FSCH
3
4.7UF
5-1