To 1.1V, -Analog, Dc, Video Interface Circuit Description - Ceronix 1493 Service Manual

5.6V to 1.1V, NEGATIVE ANALOG, DC COUPLED, VIDEO INTERFACE CIRCUIT DESCRIPTION.
Red Video Amp.
Green Video Amp.
Blue Video Amp.
FIL.
H
Sync
CRT Auto Bias
V
Sync
TC7 Red
TC5 Green
TC 3 Blue
Blanking & Beam Current Limit
FDH400
084
FDH400
086
FDH400
213
4.7K
239
16 13 9 6
R G B
o o o
B
BL
R R
IN R
2 1
1N4148
340Ω
271
236
301Ω
278
R
GND
Connecter
VC
VC
RED
4
3
INPUT
In each of the video interface circuit configurations,
current from the interface circuit is converted to a
voltage at the CRT cathodes. The simplest current
path is accomplished by the negative analog video
interface configuration.
The voltage drop across the input resistors
, for the red channel, is the current which drives
236
236
the video amplifiers when the video gain line is at
8.2 volts. For a lower gain line voltage, part of the
current is directed to the +12 volt line. During blanking
all the input current flows to the +12 volt line.
Beam current
Feedback
Beam current
Feedback
Beam current
Feedback
B+G+R=∑
Beam
Current
Buffer
ABA
SOCKET BOARD CONNECTOR (TC) 206
TC 10 TC 6
End Vertical Blanking
Vertical O/S or Delayed Vertical O/S.
S
T
1.62K 604Ω
260 244
1.21K
258
+12V
P
G
11 10 3
A +12V A
+ EN - BL
Controls XRC5346A
G G
IN R
14 15
1N4148
340Ω
270
218
340Ω
277
GND
Video
G
VC
GREEN BLUE
292
5
INPUT INPUT
278
278
SOCKET BOARD
ARC PROTECT
Auto
Bright
VIDEO GAIN
U
LINE
1.21K
4-7VDC
1.62K
5-9Vpp 61,B4
076
245
2.7K
064
0Ω, CS=.30"
228
5 12
12V
TTL M
GAIN
VC
0
241
4
GND
B B
IN R
7 8
1N4148
301Ω
268
266
301Ω
276
and there is no video amplifier output.
B
green channels, a 1 volt change at the video input
VC
6
produces a 15 volt change at the video amplifier output.
For the blue channel this change is 18 volts but resistor
subtracts the equivalence of .6 volts from the input
265
265
which results in the same saturated color as the red and
green channels.
The clamp diodes
maximum current to the video amplifiers. This avoids
and
over driving the video amplifiers when undershoots at
the input cables are present. The clamp reference
voltage is set by resistors
transistor 274
274
buffered clamp voltage.
800
TC11
CRT
TC12
+127V
127V TC8
+
100uF
209
Remote
PCB
Control
1K
+12V
Vs
062
M. GAIN
RC2
1K
485
GND
+12V 11.5V-12.5V
GND
Note:
0Ω
+
The clamp
100uF
293
267 diodes are
installed
backwards with
respect to the
PCB legend.
+12V
3.92K
PN2222
272
3.5V
274
1K 2.15K
275 273
271 , 270 , & 268
271 270 268
, , and buffer
273
272 273
272
. Load resistor stabilizes this
275 275
0VDC Hs
56V 28,D3
Filament
Fil. Ret.
Screen
Focus
EHT
+16V
+12V
GND
271
270
268
For the red and
limit the
65