To .7V, +Analog, Dc Video Interface Circuit Description - Ceronix 1493 Service Manual

0V to .7V, POSITIVE ANALOG, DC COUPLED, VIDEO INTERFACE CIRCUIT DESCRIPTION.
To Video Board
FDH400
TC7 Red
TC5 Green
084
TC 3 Blue
FDH400
086
FDH400
213
16 13 9 6
R G
o o
R
IN
2
A5
J
75Ω
278
R
VC
RED
4
INPUT
For DC coupled positive analog video signals, the
signal source black level is 0 volts. The standard
saturated color voltages are .7 volt and 1 volt.
The RGB video signals and sync are connected to
the monitor through the video input connector
Resistors , , &
288 286
288 286
lines and load the input such that, when no signal
source is connected, the screen is dark.
Resistors ,
278 277
278 277
interface IC from transients. They also act as
241
241
load resistors for the clamp diodes. The clamp diodes
, , & limit the peak amplitude of the
271 270 268
271 270 268
video, to prevent overdrive of the video amplifiers.
These diodes are connected to transistor
resistor . The base to emitter voltage of the
275
275
transistor balances the clamp diode's forward
274 274
voltage for temperature compensation. Resistors
and set the clamp voltage.
273
273
The gain of the input circuit is set by resistors
, & .
264 232
264 232
66
Blanking & Beam Current Limit
1.62K
260
+12V
11.5-12.5V
GND
15.8K
261
11 10
B A +12V
o + EN
B
BL
Controls
R G
R IN
1 14
B5
0Ω
15.8K*
K
225
1.87K
223
0Ω
75.0Ω
218
226
1N4148
75Ω
271 277
75Ω
GND
288
G
GND
VC
VC
GREEN
292
5
3
INPUT
292
292
terminate the video
284
284
, & protect the video
276
276
and load
274
274
S T
U
604Ω 1.21K
1.62K
244 245
2.7K
1.21K
064
258
0Ω
228
5
3 12
A
TTL M
- BL
GAIN
241
XRC5346A
GND
G B
R IN
15 7
A5
0Ω
15.8K*
L
243
2.15K
242
84.5Ω
264
1N4148
75Ω
270
276
75Ω
GND
286
BLUE
B
INPUT
VC
6
Resistors
across the gain resistors to offset the voltage drop
caused by the .6mA bias current across the input and
protection resistors. +12 volts to these resistors
produces a fixed black level. An optional black level
.
adjustment may replace the +12V with a range of
0 volts to 11.3 volts. Potentiometer
transistor
221
221
adjustment voltage.
The master gain line is connected to the video
interface IC
by the gain resistors
Vertical and horizontal blanking set the gain to 0
during retrace. The gain is adjusted by the master
gain control
maximum gain may also be limited by making solder
connections
272 272
Diodes
084 084
226 ,
226
connected to the video board to prevent damage to the
video interface IC from arc related voltage spikes.
VIDEO GAIN
LINE
1K
4-7VDC Vs
062
5-9Vpp 62,B4
076
RC2
+12V
GND
0Ω
+
100uF
293
267
12V
VC
0
4
PN2222
B
R
8
56pF
205Ω
221
234
265
0Ω
15.8K*
233
2.15K
231
88.7Ω
070
232
PN2222
1N4148
268
75Ω
274
30Ω
284
275
GND
, , & produce a voltage drop
223 242 231
223 242 231
and resistor which provide the
219
219
at pin 12. It multiplies the gain set
241
241
, , etc. by 0 to 1.
225 226
225 226
through load resistor
485 485
, , & .
S S T U U
T
, , & 213 clamp the video lines
086 086 067
Remote
PCB
Control
+12V
M. GAIN
1K
485
GND
GND
*Replace
with a
221
0Ω jumper
for fixed
black level.
0Ω
219
10K
GND
+12V
3.92K
272
412Ω
273
is buffered by
070
070
. The
062
062