MEA 1786FD2
CRT Monitor Service Guide
Circuit Operation Theory
18
30. Video CKT
VIDEO C.K.T. BLOCK DIAGRAM
:
PREAMP
CKT
LM1279
IC101
CRT DRIVER
CKT
LM2439
IC102
ABL CKT
Q322,323
R OSD
G OSD
B OSD
CONTRAST
(FROM IC801)
BEAN CURRENT
(FROM F.B.T.)
H-BLANK
CKT
Q320
H-PULSE
(FROM F.B.T.)
(FROM
IC 1901 )
R
G
B
DRIVE
(FROM IC1901)
DC RESTORE
Q121,122
Q141,142
Q161,162
R
G
B
BIAS
(FROM IC 1901)
R
G
B
G1
BRIGHTNESS CKT: Q203
CHANGE MODE BLANK CKT:Q202
V BLANK CKT: Q202
SPOT KILLER CKT: Q202
R
G
B
VIDEO
CUT
31. OSD Preamp CKT:
(a) AS shown in the block diagram:
The R/G/B signals will generate an enough amplitude of Vpp to show up on the
CRT screen after the amplification of two amplifiers. The first one, preamp CKT,
process the signal and mix up the OSD, and the second one does the power
amplification.
(b) OSD preamp IC101, LM1279, will output the R.G.B signals seperately. The R.G.B
driver will control the gain of these three guns individually to approach the white
balance of CRT.
(c) The signal H-Blank is to let the output of LM1279 down to 0.2V while non-display
duration. Then the CRT driver CKT will generate a level higher than Black Level. (i.e.
SYNC TIP), therefore the video signal will be blanked in order to prevent the fold over
to occure while adjusting H-phase. Besides, the SYNC TIP is used for
the DC Restoration of cascode CKT.
(d) LM1279 is equipped with OSD mixer. when signal CUT is Low, the output of
LM1279 is video signal when signal CUT goes high, the output will be OSD signal.
32. CRT DRIVER CKT:
Содержание 1786FD2
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