DEC VT220 - 8.2.3 Flyback Transformer Circuit

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 1I
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 IN5623
-
6.8M
)
d
R220
P207
ID201
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