Samsung DVD-V5450, Service Manual

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Circuit Operating Descriptions
13-23
Samsung Electronics
91
IC301 LA71750/30M
96
91 92
91 93
91 90
87
70
71
61
CH1
AMP
AMP
AMP
AMP
CH2
S P
H'D
SLP
H'D
CH2
CH1
H'D S/W
H'D AMP S/W
VIDEO OUT
FM AGC
NL
DEEMPHA
YNR Y/C
COMB
PB
FM-EQ
PB EQ
PHASE
DOUBLE
LIMIT
FM
DEMOD
6dB AMP QV/QH
F.B
CLAMP
Y/C MIX
PICTURE
CTL
MA2N
DE-EMPHA
SUB
LPF
CLAMP
CCD
3.5MHZ
LPF
91 43
91 46
NOISE
CANCELL
(2) Luminance Signal Playback System
Fig. 13-22 Luminance Playback Process
1) Outline
The video signal recorded on the tape is picked up by CH1, CH2 head and is supplied to pre-amp block via
rotary trans. During playback, as per the speed, SP and SLP head is determined by Pin70 of respectively.
CH1 signal inputs to Pins 87 and 96 while CH2 signal inputs to Pins 90 and 93 of video IC. The pick up operation
is controlled by the head switching pulse inputted to pin 70. During the high portion of the switching pulse, CH2
is picked-up and just the opposite is true for CH1. In the pre amp IC, the FM signal is amplified 60dB and this
signal is applied to FM AGC.
2) FM AGC AMP
At the FM AGC Amp (FM), signals are automatically balanced. One of the AGC circuit outputs is fed to AGC
detector circuit which detects signal level fluctuations. The detector output signal is applied to the FM AGC Amp
to keep the output constant.This output is applied to the PB FM EQ block. FM EQ is correct the phase distortion
and level. The signal through PB EQ circuit is applied to the double limiter.
3) Double Limiter Circuit
A FM signal on the tape which contains AM components will be read during playback. If there is a severe AM
component, a drastic drop in FM carrier can occur. This lack of FM carrier can be called a noise region. Double
limiting is used for improving the S/N ratio and carrier loss. The playback FM signal is split into two paths, one
goes to high pass filler and sub-limiter. The other goes to the main-limiter after passing through a LPF. ONE path
of the FM signal goes to the high pass filter, so that the low frequency(AM) component can be removed, and the
other carrier is supplied to the sub-limiter. The output signal of sub-limiter is mixed with the signal from the
low-pass filter and sent to the FM demodulation circuit.