Ceronix 1493 Service Manual page 53

Blue Video Amplifier
+12V
2
Ω
301
K2
MMBT
3904
K34
Ω
606
K7
Jumper
K33
1N4148
100Ω K36
K21
681Ω
1
K6
K6
1N4148
1.62K
K35
K1
+12V
VIDEO INTERFACE
R G B
VIDEO SOURCE (external)
The bias current of the push-pull output
stage is set by resistors
, and diode connected transistor
K17 K17
Transistor is thermally connected to
950 950
transistor to maintain the same base to
951
951
emitter voltage drop. Note that resistor
adds 11mA to the diode connected transistor
. This current is available to drive the
950 950
base of transistor
951
951
frequency amplification. This high base
current is needed because, the beta of
transistor is low for high current pulses
951 951
and when high frequency is amplified many
high current pulses occur. The mechanism
for transferring the current from
VIDEO AMPLIFIER SCHEMATIC.
937
10
1.49K
K9
40.2K
K19
10
1
7
3
SOT
NE592
1.0K
K8
K32
12
8
14
5
.1uF
934
3pF
A
5.62K
K11
21K
836Ω
K22 K10
5 9
VERTICAL and
HORIZONTAL
MG
BLANKING,
Master Gain, &
Beam limiter
, , ,
K14 K14 K15 K15 K16 K16
950
950
K17
during periods of high
3
18
Ω
560
MPS2907
K17
12.1K
K15
17
Ω
140
B14
K16
16
.015uF
10
885
20
3
Ω
150
2SC
.5W
K3 3467
K3
4
MPS2907
Ω
33
8
K20
9
945
11
2.2K 3.32K
K5
K12
12
GND
transistor
950
950
is the coupling capacitor
through resistor
the signal and discharges through the base of
transistor
951
951
drive signal. Therefore the output stage,
.
bias current, is frequency dependent and has
a range of 3mA to 15mA.
Resistor
K17
connected to the 9.25 volt line, decouples the
video amplifier current pulses from the 127V
line. The 9.25 volt line is connected to the
emitter of the NPN push-pull transistor by
resistor
K4 K4
output voltage of the NE592 in the middle of
it's ±2 volt drive range. The 9.25 volt line is
regulated by darlington transistor
voltage divider resistors
.1uF
957
Ω
75
K13
950
Ω
18 14
K14
.1uF
2SA
15
250V
1370
887
951
7
19
9.25V
Ω
180
Dark screen
K18
80-110VDC
1nF
PART
Ω
205
956
OF
953
FDH400
AUTO
BIAS
943
958
7
1.8K
2SA
Ω
15
955
6
1370
K4
1.8K
948
954
BIAS CONTROL LINE
1.8K
MPS A64
938
942
D
3.92K
940
GND
to the base of transistor
which charges
885
885
on the positive part of
K16
K16
on the negative part of the
and capacitor
K13 K13 887 887
. This voltage establishes the
&
938 938 940 940
127V
16V
120V
13
BLUE
VIDEO
TO
CRT.
Beam
Current
Feedback
FROM
CA3224
GND
+12V
9.25V
.1uF
930
951
951
, which are
with
942
942
.
69