Samsung MAX-485 - Page 26

6-4. CD section
1) RF Amp (KA9220) : WICO1
RF I-V Amp (1) and RF I-V Amp (2) are converted to voltage via
internal resistance of 58k 2 from the current of PD1 (A+C) and PD2
(B+D); then, this voltage is added to RFsumming amplifier.
The signal (A+B+C+D) is applied to RFO ( No.2 terminal).
RF output voltage can be calculated as follows:
VBF = -R3 x (iPD1 + iPD2)
= -R3 x (V1/R1 + V2/R2)
= -R3 x (V1/10K + V2/10K)
= -R3/10K x (V1 + V2)
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 voitage 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)
This FOCUS ERROR voltage is sent to FOCUS SERVO circuit to
maintain optimum focusing.
3) FOCUS SERVO SYSTEM (KA9220) : WICO1
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 pin 18 and GND has the time constant picking up the low frequency operated in PLAY mode.
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 pin 22, 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(pin 69) (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.
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