Panasonic BT-M1950Y Service Manual page 86

BT-M19:;uv
3. Video processor
The Y and color difference signal inputs to IC402 are applied to a matrix circuit to produce RGB (V.YN/RGB). The RGB
signal inputs from the RGB input terminals and on-screen RGB signals (OSD RGB) from the MPU are switched by VOB
and RGB/-OTHER from the MPU. The relationship between switching and selected signals is indicated in Table 3-1.
VOB RGB/-OTHER OSDRGB RGB V.Y/CRGB
L
L
0
L H
0
H
X
0
Table 3-1
The respective R, G and B outputs from pins 24, 22 and 20 are sent through buffers 0451, 0452 and 0453 to the CRT
socket PB ASS'Y.
OBlue
check circuit
The blue check function cuts off the red and green signals to leave only the blue signal. The function is used ·1or
chroma and phase checks and adjustments. When the front Blue Check button is pressed, the blue check signal from
the MPU goes High to switch on 0460 and 0459. The red and green signals are grounded and only the blue signal
goes to the CRT socket PB ASS'Y to produce the blue check screen.
eVideo mute circuit
When an input is absent, the video mute function produces a black screen. 0462 switches off when -VIDEO MUTE
from the MPU is Low level. High base potential then switches 0455, 0456 and 0457 on. The red, green and blue
signals are grounded, and absence of output to the CRT socket PB ASS'Y produces a black screen.
eon-screen V sync circuit
The OSD V SYNC signal is applied via CN0Ol. At the V blanking rising edge, 0458 and 0461 switch on. Low base
potential switches off 0455, 0456 and 0457, and 0459 and 0460. Muting is applied to the upper portion of the
screen in order to avoid sync disruption.
The OSD V SYNC signal also goes to the MPU to determine the on-screen timing at the V falling edge.
VOB
CN002
10 R
18 G
14 B
TO
,cso,G)
FROM
y
IC305@ -----~
FROM -IR·Yl
IC305
(@) ---~
OSD R
OSD G
OSD B
SW
!
-0~
?
IC402
SW
Q457
Fig. 3-1 Video process circuit
-86-
VIDEO MUTE
TP-R
TO
CRT SOCKET
PCB
FROM
----DEF PB ASSY
CNOOI@