Samsung SV-DVD50 Service Manual page 125

(2) Luminance Signal Playback System
CH1 91 96 AMP
S P
91 92
H'D
91 93 AMP
CH2
91 90 AMP
CH2
SLP
H'D
CH1 87
AMP
H'D S/W
70
H'D AMP S/W 71
61
VIDEO OUT
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.
6dB AMP QV/QH
Fig. 7-22 Luminance Playback Process
PB EQ DOUBLE
PHASE LIMIT
PB
FM-EQ
FM AGC
NL
YNR Y/C
DEEMPHA
COMB
NOISE
CANCELL
F.B
Y/C MIX
CLAMP
IC301 LA71750/30M
Circuit Operating Descriptions
FM
DEMOD
SUB
MA2N
LPF
DE-EMPHA
3.5MHZ
CLAMP
LPF
CCD
PICTURE
CTL
91 43
91 46
7-23