DEC VT220 Technical Manual page 177

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8.2.3
Flyback Transformer Circuit
The
flyback
transformer
circuit
provides
high
voltage
anode
(12,500
V),
cutoff
grid
(+750
V)
and
variable
focus
grid
potentials
to the CRT, as well as operational voltage (+60 V) for
the video amp and brightness cbntrol circuits.
The
flyback
transformer
circuit
following components/circuits.
(Figure
8-13) consists of the
Flyback transformer (T1)
+60 V output (D100 and L204)
Cutoff
grid
bias network (L203, D202, R219, C219, R224,
and C220)
Focus grid bias network (R220-R221)
The outputs from the flyback transformer are controlled
the
horizontal
output
portion
of
the
horizontal
circuit.
When
Q202
cuts off, a 175 V pulse is passed
primary
of T1. This pulse results in the anode, cutoff
and video amp and brightness control voltage outputs.
by Q202 in
deflection
across the
and focus,
TO
BRiGHT"-iESS
iR
113. Cl0n
HV
ANODE
POTENTIAL
TO
CRT
TO
CRT
{CUTOFF
GRID!
TO
CRT
(FOCUS
GRIDI
TO
ViDEO AMP •
IR109\
TO/FROM
HORIZONTAL
OUTPUT
G"'D
I
Dl0C
I
RG1J
L204
!Ill
l
f - - -
[--Til
5207 PUR
P207
5
...1
T 1
I
R224
)
R219
5207 YEL
) P207
6
P;~7
41
L203
I
1M
lOOK
I
p207
P207
2I 5207 RED
1
0202
R223
Lo
5207 BRN
7
"
5207 BLU
I N5623
-
6.8M
)
d
R220
P207
I
D201
8
'-'
5207
1M
P207
I
BLK
C219
--1'02
L:
115M
5201 GRN
;; ,02
lKV
-t-~
R221
lKV
5M
R222
C218
:;:r:
lOOK
.02
lKV
b
·170V
FROM
HOR ,ZONT AL OUTPUT
(CHARGE PUMP)
FROM
DYNAMiC
FOCUS
(C222)
Figure 8-13
Flyback Transformer Circuit Diagram
8-11

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