Service manual

CA-15
Video Processing
powered by the +215V source derived from the sweep transformer, but the actual DC voltage at the
collectors will be lower (+130 volts is a good ballpark figure) because of the resistors RX5104, 5111, and
5122 and variations in the drive signal.
<<Figure CA-13>>
The emitter circuits of each driver are attached not to ground, but to a reference voltage of about +3V. This
reference voltage is established by R5114 and D5101 and serves to set a black level for the cathodes
around +165 volts. The reference voltage must be relatively noiseless, so C5107 is used to eliminate any
interference.
A number of the CA chassis provide an afterglow cutoff circuit on the CRT socket board. This circuit
makes use of the fact that with respect to the picture tube, G1 is the ground. Because C5107 takes a
relatively long time to discharge, there is the possibility that the picture tube could continue producing
electronic emissions for a short time after the receiver is turned off. The afterglow cutoff makes use of
power from the filament voltage (pin 4, connector 5F2). When the receiver turns off, the loss of this voltage
turns off Q5104. This allows for a brief moment the G1 cathode to become more positive, leaving less
potential on the other cathodes from any remaining voltage across C5107. C5110 determines the dead time
on response, and C5111 determines the rise time of the G1 voltage, both of which are between 10 and 30
milliseconds.
1
12
11
10
9
8
7
6
5
4
CRT1
R5128
PROV
W5101
1
2
3
4
5
Q5101
R5101M
C5102M
R5102M
R5103
Q5102
R5108M
C5105M
R5109M
R5110
Q5103
R5117M
C5108M
R5118M
R5119
RX5104
L5101
C5101
RX5111
RX5122
R5115
R5107
R5123
+9 VSW
R5105M
R5106M
C5103M
R5112M
R5113M
C5106M
R5120M
R5121M
C5109M
D5101
C5107
R5114
1
2
3
4
D5102
PROV
+215V
R5127
C5111
L5102
C5110
PROV
R5124M
PROV
Q5104
PROV
R5125
PROV
R5126
L5103
R5116
C5104
DAG
+215V
Blue
Red
Green
G2
G1
BLUE
GREEN
RED
G2 Wire
to Sweep
2
21
2
2
1
1
2
2
5F2
5C2
2