Video Amplifier System With On-Screen Display - NEC MultiSync FE700 Serviceanleitung

9. Video amplifier system with on-screen display

LM1281 (U201)
Outstanding features:
* Three-channel video amplifier bandwidth 85 MHz @ -3 dB (4 Vp-p output)
* OSD TTL input, bandwidth 50 MHz
* High-speed video/OSD changeover
* High impedance DC contrast control above the 0-4V, 40dB range
* High impedance DC OSD contrast control above the 0-4V, 40dB range
Red OSD Input 1 1 1 1
Green OSD Input 2 2 2 2
Blue OSD Input 3 3 3 3
Video/OSD Switch 4 4 4 4
5 5 5 5
Red Video In
V V V V
6 6 6 6
CC1
7 7 7 7
Ground
8 8 8 8
Green Video In
V V V V
9 9 9 9
CC1
10 10
10 10
Ground
11 11
Blue Video In 11 11
V V V V
12 12
12 12
REF
13 13 13 13
Video Contrast
14 14 14 14
OSD Contrast
Description of the functions
Figure 1 shows the block diagram of LM1281, in conformity with the pin layout of the IC.
Every channel accepts both the video signal and the OSD signal at the input amplifier (A1).
Also the video/OSD changeover signal passes either the video signal or the OSD signal through LM1281,
or is connected with the input amplifier for control purposes. The next contrast adjustment block is a drive
adjustment type one.
The reference level for the DC return circuit is set by means of the RGB cutoff adjustment pin (PIN 25).
Attention must be paid to the fact that the blank clamp gate is active when it is stuck at the LOW state.
Under ordinary circumstances, these pins are controlled by means of the standard TTL signal.
BLOCK AND CONNECTION DIAGRAM
Top View Top View
Top View Top View
Contrast
-A1 -A1 -A1 -A1
Attenuation
Attenuation
Contrast Contrast
-A1 -A1 -A1 -A1
Attenuation Attenuation
Contrast Contrast
-A1 -A1 -A1 -A1
Attenuation Attenuation
8 - 27
Drive
-A2 -A2 -A2 -A2
-A2 -A2 -A2 -A2
-A2 -A2
-A2 -A2
28 28 28 28 Red Drive Adjust
27 27 27 27 Green Drive Adjust
26 26 26 26 Blue Drive Adjust
25 25 25 25 RGB Cutoff Adjust
24 24
24 24 Red Clamp Cap
23 23
23 23 Red Video Out
V V V V
22 22
22 22
CC2
21 21
21 21 Ground
20 20
20 20 Green Video Out
19 19
19 19
Green Clamp Cap
18 18
18 18 Blue Video Out
17 17
17 17 Blue Clamp Cap
16 16 16 16
Blank Gate
15 15 15 15
Clamp Gate