Philips L9.2A, Service Manual

Page: 28 / 35

Circuit description new circuits
GB 60 L9.2A 9.
Figure 9-14 “VIDEOPATH”
9.6.2 CVBS/Y/C selection
The input switches are used for selection of the input signal.
Three input signals can be selected:
•
Pin 13: terrestrial CVBS input.
• Pin 17: external AV1 input.
• Pin10/11: external AV2-Y, CVBS/C input
When pin 11 is in the CVBS input mode then pin 10 is not used.
When pin 11 is in the Y/C input mode then both pins are used
and the CHROMA filter in the Y signal path is switched off.
9.6.3 Luminance / Chroma signal processing
Once the signal source has been selected, CHROMA filter
calibration is performed. The received colour burst-sub-carrier
frequency is used for the calibration. Correspondingly, the
CHROMA band-pass filter for PAL/NTSC processing or the
cloche filter for SECAM processing is switched on. Pins 34, 35
have the crystals connected to them. These crystals are used
for multi-purpose calibration of the burst sub-carrier. The
selected luminance signal is then supplied to the Horizontal
and Vertical synchronisation processing circuits and to the
luminance processing circuits. In the Luminance processing
block, the luminance signal is applied to the CHROMA trap.
This trap is switched on or off depending upon on the colour
burst detection of the CHROMA calibration circuit. Before the
luminance signal is applied to pin 28 of the TV-processor the
signal is applied to a "peaking" and "coring" circuit. In these
circuits the sharpness and noise level of the signal can be
influenced via the remote control (control menu in the user
menu ).
9.6.4 PAL, NTSC and SECAM demodulation via the Auto system
manager
The colour decoder circuit detects whether the signal is a PAL
or NTSC signal. The result is made known to the auto system
manager. The base-band delay line is activated when a PAL or
SECAM signal is detected. For the SECAM colour standard a
reference voltage is generated at pin16 of the TV-processor.
Connected at Pin 9 of the TV-processor, is the band-gap de-
coupling circuit, which consists of (2214,2215). The band-gap
circuit provides a very stable and temperature independent
reference voltage. It ensures optimal performance of the TV-
processor and is used by almost all functional blocks inside the
processor. The Y signal and the demodulator outputs R-Y and
B-Y are present at pin 28, 29, 30 of the TV-processor. The auto
system manager identifies PAL, NTSC and SECAM colour
standards and is controllable via the IIC bus. Connected on pin
36 of the TV-processor is the Loop Filter for the phase detector
The filter chosen provides an optimal transient response, which
ensures both an optimum for noise bandwidth and colour
acquisition time.
9.6.5 YUV / RGB processing/ black stretching
The signal Y, R-Y and B-Y present on pins 27, 31, 32 of the TV-
processor are used as the input signals for the colour decoding
section of the BiMOS (IC7520-C). The YUV processor enables
the colour saturation control and also converts the Y, B-Y and
B-Y signals to the R, G, B signal format via the colour matrix
circuit. The black stretcher circuit , initial stage of the matrix
circuit, extends the Grey signal level towards the actual black
level. The amount of extension depends upon the difference
between actual black level and the darkest part of the incoming
video signal level. This feature is fully integrated. The user can
switch this circuit on or off by using the Contrast Plus option in
the user menu.
IC 7250-4A
TDA 8845 7250-4B
TDA 8844/45
7250-4C
TDA 8844/45
7250-4D
TDA 8844/45
IC 7250-4A
TDA 8844
AGC
AGC
SOUND
IF
AMPL.
QSS MIXER
+
SOUND
AM DEM.
AFC
AFC
VIDEO
AMPL.
VIDEO-
BASE-
BAND
OUTPUT
IF AMPLIFIER
+
PLL VIDEO DEMO.
54
49
48
3 4 5
6
AGC
AFC AFC
VIDEO
AMPL.
VIDEO-
BASE-
BAND
OUTPUT
IF AMPLIFIER
+
PLL VIDEO DEMO
54
49
48
3 4 5
6
55
55
1
1
2
2
56 15
15
53
53
LIMITER
PLL-
AUDIO
FM DEMO.
AMPL.
+
MUTE
OUTPUT
+
VOLUME
CONTROL
16 9 36 35 34 33
PAL/NTSC/
SECAM
DEMODULATOR
CHROMA
BANDPASS
BASE-
BAND
DELAY
LINE
LUM.
DELAY
PEAKING
CORING
28
29
30
13
17
10
11
38
VIDEO IDENT
Y (TO SYNC PART)
CD MATRIX
+
SATURATION
CONTROL
+
SKIN
TINT
27
31
32
7 8
21
20
19
18
22 23 24 25 26
Y
U
V
RGB
MATRIX
+
BLACK
STRETCH
+
RGB1
INPUT
IIC BUS
CONTROL
R
G
B
R
G
B
RGB
OUTPUT
CATH.
CALIB.
41 42 37
SYNC.
SEPARATOR
VCO
+
CONTROL
HORIZONTAL
OUTPUT
VERTICAL
OUTPUT
E/W
OUTPUT
VERT.
SYNC.
SEPARATOR
Y
43
50
40
46
47
45
52 51 44 39
CL 86532104_021.EPS
220299
OR
INPUT SELECT
Y + CHROMA
PROCESSING
RGB
OUTPUT
SYNC
YC/CVBS EXT
YC/CVBS EXT
CVBS + SIF
R
G
B
TDA884X
SWITCH
V_PATH1.PPT
20/3/98
TUNER
SOUND
TRAP
IF
CVBS_INT
SOUND
BPF
SIF
(to sound proc..)
CVBS_EXT
CVBS_MON
IF
48/49 25
21
32 38
6
13
17
30 29 28 27 31
19
20
24 23 26
CHROMA
PROCESSING
MATRIX
RGB
PROCESSING
+ SWITCH
YC/CVBS EXT
R G B FBL
OSD/TXT/SCART
TO CRT
Y
U
V
CL 86532104_017.eps
160299
TDA 8844/8845