Samsung MAX-557 - Page 35

3-2. CD section
1) RF Amp(KA9220) : NIC9220
RF {-V Amp(1) and RF !-V Amp (2) are converted to voltage via
internal resistance of 58kQ from the current of PD1(A+C) and PD2
(B+D) ; then, this voltage is added to RF summing amplifier.
The signal (A+B+C+D) is applied to RFO (No.2 terminal).
RF output voltage can be calculated as follows:
R1 RF SUMMING
V1 AMP
VRF = -R3 x (iPD1 + iPD2)
=-R3 x (V1/R1 + V2/R2)
=-R3 x (V1/10K + V2/10K)
=-R3/10K x (V1 + V2)
2) FOCUS ERROR Amp(KA9220) : NIC9220 FOCUS ERROR Amp is the circuit which amplifies the
difference between RF I-V Amp(1) output(A+C) and RF I-V
RO 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 depending on { (A+C) - (B+D)
}.
VFE can be obtained as follows.
VFE = (R2/R1) x (V2-V1) = 5.4(V2-V1)
FE Bias
This FOCUS ERROR voltage is sent to FOCUS SERVO
MAO Sac circuit to maintain optimum focusing.
3) FOCUS SERVO SYSTEM(KA9220) : NIC9220
The diagram of Focus Servo System is shown in the following.
When FS3 is ON, high frequency gain decreases in the form of low frequency time constant by pin 17, pin 19, and
capacitor connected to internal resistance.
The capacitor between pin18 and GND has the time constant picking up the low frequency operated in PLAY mode.
PHASE
COMPENSATION
The maximum frequency of focus phase compensation is inversely proportional to the resistance connected to pin7.
Focus search peak is about 1.1 Vp-p, and is inversely proportional to the resistance connected to pin22,23 ; however,
if this resistance changes, the peak of track jump and sled kick changes.
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 pin 7 changes, the phase compensation peak of focus, tracking, sled servo
changes. At the same time, ‘op-amp’ dynamic range and offset voltage also change.
Ley.
MAX-550