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5.2.0 FUNCTIONAL CIRCUITS
Circuits on the display PC board generate, accel-
erate, deflect, and intensify the electron beam.
These circuits are described in the following
paragraphs.
5.2.1 High Voltage Oscillator
B
The high voltage oscillator is free running. The
oscillator and the high voltage converter generate
the 400-volt and 12,000-volt levels from the
12-volt supply. A time delay circuit on the dis-
play PC board prevents the high voltage oscillator
starting for approximately 15 seconds after the
machine is truned on to prevent damage to the
CRT during filament warmup. A current detec-
ting circuit on the display PC board monitors
the high voltage oscillator current at all times.
If the oscillator current exceeds the limits, the
oscillator is turned off for approximately 15 sec-
onds. The high voltage converter has two out-
puts; one output is 12,000 Vdc, the other is
400 Vdc. The 12,000 volts accelerate the elec
tron beam; the 400 volts control the brightness.
5.2.2 Brightness Control
0
The brightness control is located on the CE con-
trol panel. The center tap voltage of brightness
control is fed to the video (dot) amplifier. It
controls the bias voltage on the cathode of the
CRT. The bias voltage can be varied from approx-
imately +30 volts to approximately +120 volts
by turning the brightness control potentiometer-
Display PC board
Converter
High
m
voltage
High voltage
ground
o~;cillator
1 - 5 1 - - - - - + - - - - - - - ,
~1--,
r----I-~I_-r--
f - - - - - -
0 < ) 0
I
.J...
~
T
T
>0
r---~
:;;- --, ...1..
-D12
-D13
IC>
I
'--1
I
T
I
"----+---1 - - - -
--+..J
I
- D 0 7 - 4 -
: -..... --.- -
-
_Si_'JI'~iO~~
{7400VdC
-
D08--.J
81----;=====::;'1
L __
L~ ~_
~----
+ 12 Vdc
~_+---,8rightnes
f-4 -
--~
FeedlJdck
~ (oscillator)
..... 5·-
-
808
n1
~~'ontrOI
-809------11 - - · - - - 1 0
~
~--~----~==::::::::::::::::~~OnCE
1
Panel
.-
---
-
- - - 1 2
- t
12 V d c - - - - - - - - - - - - - - J . . . - - - - - - .
Horizontal
master
5-2
Wiggle control
- 8 0 5
Character
(wigyle
13 -W,ygle sweep pulses
------------li--. . . . .
;weep)
P.:I
m
,:ontrola
---14~-------------~
----15~--------------~~
-=: , ' - - - - _ _
CRT
~~:
'
!
' - m
Chassis
I
Video (dot)
--807
illl1plilier
1 7 I - V i d e o - - - - - - - - - - - . f - - - J
Vidvo
+6
Vdc
I- -- -
-
-
-812--.....-
,-I--'---18-Heater+6
Vdc
- 8 1 3 - - - - - '
Character
yoke
~
F
Horizontal
slave
~ I~
CRT
~\)
yoke
{
B02
-
- - -
--r:I
Vertic,!!
==:B(13----I Vertical line&:!
_ _ _
-I~control
A - Vertical d e f l e c t i o n - - - - - - - - - - - . . . J
--804
__ , _ _ _ .
Hcrizontal
8 -Horizontal deflection - - - - -_ _ _ _ _ _ _ _ ~I_I
Horizont~J
- - B 1 0 - - - - I
sw~ep
_(r::.~flllect~ ~
-Horizontal deflection
+12Vdc
--D09---~
..... - -
r - 0 - + 1 2 V d C - - - - - - - - - - - - - - - - - - - + - J
/13
V),8
Pins
-D1O
---c
E -+12 Vdc
E:P
"------~.'I
D Pins -12 Vdc
/ F -+12 V d c - - - - - - - - - - - - - - - - - - - l
I
- - D 0 2 - - - - - I . , / " "
the lower the voltage, the greater the light
intensity on the CRT.
Plant---
Date--
PN-----
E C - - -
(Back side)
BR
B l u - - - - ,
Character Yoke
Brightness Control
Converter
Display PC board
PC Board Pi ns
Ground for
GE
Probe
PC 17 (yellow)
PC 16, 18
(brOWn)~7
6
~lfa/
PC 14 (black)
-\~......(X
y~ ~C
15 (orange)
PC 8 (red)
CRT Socket
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