Daewoo DV-K*04W Series, Руководство по обслуживанию, Страница: 20 / 114

CIRCUIT 17
2. REC MODE
(1) Signal Flow
In this system, the input signal sources are contained with IF, AV and F.AV. each pin number’s decription is the same
as the below.
The input signals, selected by the input siwthcer, go through the LPF (at 20KHz) and PNR processor. Additionally, the
selected input signals are supplied to the Normal Audio Unit-Pin 31st. The Normal Audio cab be mixed with the L+R-
Stereo mode, or can be selected with L only-Bilingual mode. The PNR processor compresses the audio signal in order
to reduce the audio noise and enlarge the Dynamic Range.
The FM EMPH(FM Emphasis) emphasiszes the higher band of signal. It can restrict the FM back-noise, when the
signal is demodulated. The modified audio signal is modulated by the Modulator unit. It is composed of AUDIO
LIM(Limitter), 1.4MHz & 1.8MHz (NTSC Case: 1.3MHz & 1.7MHz) modulator. The Audio limiter cuts the level of signal
to avoid the overmodulation, and then the limitted signal is modulated with two carriers-1.4MHz : Left Ch, 1.8MHz :
Right Ch. The modulated two signals are mixed by the FM MIX unit. The mix ratio of FM L and R can be adjusted with
the software-refer to the service mode. Finally, REC FM signal put out to the Pin 21st. It is supplied to the Hi-Fi
preamp.
(2) Auto Adjustment of the VCO, BPF
In this IC, the FM carrier frequency and BPF are adjusted by the synthesized PLL VCO (Phase Locked Loop Voltage
Control) unit. The Auto adjustment is executed at POWER ON, as using the Fsc-3.58MHz. The Fsc is supplied from
the OSC for Color Sub-carrier in the Video unit. If the adjustment completes successfully, IC’s pin 14th is set the
“HIGH” state-5V. Otherwise “LOW” state-0V. The adjustment of VCO, BPF occurs simultaneouslly.
L
R
8 21
LPF
INPUT
SW
31
PNR
FM
EMPH
LPF
LPF PNR
FM
EMPH
LPF
1.4M
MOD
AUDIO
LIM
REC FM
LPF
Fsc
AUTO
ADJ
FM
MIX
REC FM OUT
1.8M
MOD
AUDIO
LIM
REC FM
LPF
INPUT
IF AV F.AV
CH
L 2 41 34
R 1 40 33