Special Circuit Descriptions; Cd; Rf Amp (Ka9220); Focus Error Amp(Ka9220) - Samsung MAX-670 Service Manual

5. Special Circuit Descriptions

5-1 CD

5-1-1 RF Amp (KA9220) : WIC01
58K
65
B
PD1
A C
RF I-V AMP(1)
58K
PD2
D
66
Photo Detector
RF I-V AMP(2)
5-1-2 FOCUS ERROR Amp(KA9220) : WIC01
R1
V1 32K
-(B+D)
-(A+C)
32K
C2 25P
5-1-3 FOCUS SERVO SYSTEM (KA9220) : WIC01
When FS3 is ON, high frequency gain decreases (time constant set by pin17, pin19, and capacitor connected
to internal resistance).
The capacitor between pin 18 and GND sets the time constant to pass the low frequency operated in PLAY mode.
FE1
20K
0.1UF
The maximum frequency of 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 inversion 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 focus, tracking, sled servo changes.
At the same time, 'op-amp' dynamic range and offset voltage also change.
Samsung Electronics
RF SUMMING
R1
V1 AMP
10K
RFO
66
74
R3
10K
73
R2 V2
RF
FOCUS ERROR Amp is the circuit which amplifies the difference
R2 between RF I-V Amp(1) output (A+C) and RF I-V Amp(2)
174K
output(B+D).
C1 25P
These two signals are supplied to (-) and (+) input terminals of
FOCUS ERROR Amp. The FOCUS ERROR signal resulting from this
FE
difference voltage is applied to FE (Terminal No.57).
59
The FE output voltage of this low frequency component varies
FOCUS
according to {(A+C) - (B+D)}.
ERROR
AMP
164K
VFE is calculated as follows :
V
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) are converted to voltage via
internal resistance of 58k½ from the current of PD1(A+C) and PD2(B+D):
This voltage is added to RF summing amplifier.
The signal (A+B+C+D) is applied to RFO (No. 66 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