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3) G2 and Beam Current Sensing Functions
- Amplifies setup levels provided by Preamplifier A/D outputs for G2 control.
- Beam Current Feedback (BCF) sensing for Color Restoration function.
4) Display Data Channel Interface
- DDC2Bi
- DDC2B
1. RGB Signal Processing (A Board)
RGB Signal Select
The Video and Sync inputs from the rear D sub and front input connectors are applied to the inputs of IC008. Each input is
terminated by an 82 Ohm resistor which is seen as 75 Ohm termination due to effect of the input impedance of IC008. IC008
switches between inputs, at the user's discretion, when the input select button on the front panel is accessed. A low on IC008
Pin (9) selects the rear D sub input. Sync timing signals are buffered by IC008 before being sent to the N board. Sync on
Green timings are passed to IC001 where the sync signal is isolated and then sent to the N Board.
RGB Signal Amplifiers
Selected and buffered RGB video signals are amplified by IC001. Here the individual Sub Contrasts, Brightness offsets, and
Contrast gain levels are set by the Microprocessor via I2 C control. The OSD RGB video signals from IC003 are mixed into
the main video channels inside IC001. IC002 provides a final amplifier stage for the RGB video signals. This video driver
is internally set to a gain of –14. Therefore at the output pins of IC002 (Pin1, 3 & 5) the waveform is inverted with typical
drives levels on the order of 45Vpp. The Video Driver IC002 drives the CRT cathodes via AC coupling.
RGB Cathode Cutoff Amplifiers
The Red cathode DC cutoff level is amplified by IC004. It is controlled by the D/A output of IC001. The Red cutoff level is
+5V
IC008
R1
27
30
R2
35
G1
G2
B1
B2
V1
21
V2
22
H1
H2
SW
Sync Processing Circuit
Logic Sync BufferIC006
To N Board
Video Select and RGB Process Functions
+12V
+5V
IC001
8
22
11
20
R
9
G
24
7
B
27
2
I
C
1
2
I
C
2
CLK
18
BPCLP
12
3
Cutoff Circuit
R OSD
4
G OSD
14
5
B OSD
13
6
17
30
R107
OSD BLK
C105
D/A G2 Control
8
9
10
5
4
6
H Sync
V Sync
C Sync
-
23
+12V
+80V
IC003
10
6
D104
C106
8
5
C206
9
3
C306
1
11
Video
Driver
+B
D106
D206
R119
D306
R120
R105
IC004
4
7
10
9
V-
-
V+
+
13
D108
R108
R116
C121
R115
C108
D120
R122
To IC003 A/D
Converters
Beam Current Sensing Circuit
Green and Blue
-
CRT
+B
+B
R219
R316
R220
R320
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Troubleshooting
