Iiyama Vision Master Pro 451, Руководство по обслуживанию

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4-6. VIDEO circuit
(1) Pre-amp
The video signal from D-SUB connector via IC101 (SW-IC) is input to pins 1 (R-IN), 3 (G-IN) and 6 (B-IN) of IC201
pre-amplifier. This video signal is clamped by clamp signal input to pin 13 of IC201. The blanking signal input
to pin 14 is synthesized with the clamped signal and then output from pins 29 (R-OUT), 27 (G-OUT) and 25 (B-
OUT) respectively.
V-BLK signal: Remove the raster retrace line.
H-BLK signal: Remove the side raster rolling.
I
2
C-BUS controls D/A converter in IC201 as follows:
Q
Contrast
R
Sub-brightness
S
R/G/B drive
T
OSD contrast
U
D/A output for the CUT-OFF circuit
V
Gamma correction
W
Sharpness correction
(2) ABL
DC voltage input to pin 7 of IC201 controls the amplitude of the video output signal. Therefore, it controls the
FBT beam current.
ABL is activated (entire white raster): Approx. 3.5VDC at pin 7
ABL is not activated (window): Approx. 4.1VDC at pin 7
The parabolic waveform is added to video output signal by synthesizing the H-DBF parabolic waveform from
Q301 and it corrects a luminance difference between the left and right side of the picture.
(3) VIDEO-OUT and CUT-OFF circuits
The video signal input to pins 9 (R-IN), 8 (G-IN) and 11 (B-IN) of IC202 (VIDEO-OUTPUT) is amplified reversely
and then output from pins 3 (R-OUT), 5 (G-OUT) and 1 (B-OUT) respectively.
The R/G/B-cut-off and brightness D/A control voltages output from pins 18-21 of IC201 pre-amplifiers are
amplified by IC204 (CUT-OFF-IC), and then added to the video signal from IC202 and supplied to the CRT
cathode grid.
CRT cathode input
(20V/div)
IC201 pin 13 clamp input
(5V/div)
IC201 pin 7 ABL input
(2V/div)
IC201 Video output
(10V/div)