SAMSUNG MAX670
Manual de Servicio

5. Special Circuit Descriptions
5-1 CD
5-1-1 RF Amp (KA9220) : WIC01
58K B A D Photo Detector C

65
PD1 PD2 RF I-V AMP(1) 58K

R1 10K

RF SUMMING V1 AMP

RFO

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 :

74 66
R3 10K R2 V2

VRF = -R3 x (iPD1 + iPD2) VRF = -R3 x (V1/R1 + V2/R2) VRF = -R3 x ( VRF = R3 10K V1 10K

66
RF I-V AMP(2)

73
RF

+

V2 10K

)

x (V1 + V2)

5-1-2 FOCUS ERROR Amp(KA9220) : WIC01
R2 174K C1 25P R1 V1 32K -(B+D) -(A+C) 32K C2 25P 164K FOCUS ERROR AMP FE

59

FOCUS ERROR Amp is the circuit which amplifies the difference between RF I-V Amp(1) output (A+C) and RF I-V Amp(2) output(B+D). These two signals are supplied to (-) and (+) input terminals of FOCUS ERROR Amp. The FOCUS ERROR signal resulting from this difference voltage is applied to FE (Terminal No.57). The FE output voltage of this low frequency component varies according to {(A+C) - (B+D)}. VFE is calculated as follows :
VFE = (R2/R1) x (V2-V1) = 5.4(V2-V1)

This FOCUS ERROR voltage is sent to FOCUS SERVO .

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.
3.6K

60K FE1 20K 0.0022

FZC 20K 48K FS4 130K FS2 470K 46K 580K FS3 FSW 0.1UF 40K FS1 PFSET FSCH 4.7UF 10K 50K 92K PHASE COMPENSATION 40K 5.5U 11U

58 60
0.1UF

FE2 470K

48

FSEO FOCUS COIL FCE

120K

DFCT FDFCT

47 20 ISET

62
0.1UF

HFGD EFR

61

180K

21
VREG

27

6

3

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 5-1