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6.7.1.4 Field
timebase
The
field
timebase
functions
are
performed
by
the
TDA2653A
integrated
circuit
D2
and
its
pe-
o~
1
6.7.1.7
Dynamic
focus
The
difference in
the
electron
beam
path
lengths
for
axial
beams and beams
reflected to
ripheral
networks.
sthe
corners
of
the
110
degr.
tube
produces
This
IC has
a
class
B
output
stage
incorpora-
ting
thermal
and
short-circuit
protection,
which
drives
the
impedance-matched
field
coils
L3
in series
connection.
The +22V
required
to
energize the
field
time
base
is
generated
by
scan
rectification
of
the voltage across win-
dings
1
and
2
of
the
line
output transformer.
Field
sync
pulses
at
TTL
levels
come
from
the
MLB
to
D2
pin 2.
6.7.1.5
Video
output
stage
The
DGD
uses
an
emitter-driven
video output
stage
with output
transistor
V105 and
driver
transistor
V106.
To
minimize
stray
capacitance,
the video
amplifier is
placed
on
the
picture
tube
circuit
board.
The +55V
supply
line for
the video output stage
is
obtained
from
win-
dings
8 and
11
of
the
line
output transformer.
The
D.C.
level
(black
level) of
the output
should
be
set
to
about
43V
via
potentiometer
VR6.
6.7.1.6 Picture
tube
supplies
All
supplies
to
the
picture
tube
are
derived
from
the
line
output transformer.
The
e.h.t.
is
generated
within
the special overwind,
which
is
constructed
in
three layers with
built
in
dio-
des,
so
that
the
D.C.
e.h.t
voltage
is
availab-
slight
variations in
the focusing requirements.
These
are
corrected
by
providing
a
parabolic
dynamic
focus voltage
waveform
in
both
line
and
field
directions.
This voltage
increases
with
deflection,
and has an
amplitude
about
250V
for
both
frequencies.
The
line
parabolic
waveform
is
obtained
direct-
ly
from across the
S-correction capacitor
C21.
For
field
frequencies,
a
parabolic
waveform
is
obtained
by
integrating
and
shaping
the
saw-
tooth voltage
across the feedback
resistor
R61.
The
same
amplifier
circuit
is
used
to amplify
both waveforms
to
the
correct
level.
Because
of
the
voltage requirements
of
the
dynamic
circuit
(up
to
500V),
this amplifier
uses two
video out
put
transistors
V103 and V104
connected
in seri
es.
The base
of
the
upper
transistor is
decoup-
led
only
for line
frequencies
so
that
the lower
transistor
amplifies only
the
field
frequency
component
of
the
waveform
and
the
upper
tran-
sistor
only the
line
frequency
component.
Both
parabolic
waveforms
are taken from
the
collec-
tor of
V103,
and
are A.C. coupled
to
the focus
electrode
of
the tube.
Because
the
electron
gun
is
a
unipotential type,
the tube
has
a
fairly
flat
focus
characteristic.
The
amplitude
of
the
dynamic
focus
can
therefore
be
preset
and
ad-
justment should not
be
necessary.
6.7.1.8 Picture
shift
le
directl
from the
screw-t
e
out ut terminal
ipícture
§hift.iS
Suppïied
1?
b°th the 1i"e
and
Y
YP
D
A
special cable with
built-in
capacitance
and
top cap,
containing
a
series
resistor
and
a
re-
sistive
e.h.t.
bleed,
is
used
to
mate
with
this
output
terminal.
The
grid
2
and
focus
voltage supplies
are
ob-
tained
by
peak
rectification
of
the
line
output
transistor collector
voltage.
This
line
also
field
directions
by
passing
a
D.C.
current
through the
appropriate
deflection
coils.
The
required voltage
for
the
line coils is
obtained
from
transformer
T3,
diode
V6,
smoothing
capa-
citor
C19, and
variable
resistor
VR3
which con-
trols
the
amont
of
shift.
The
polarity of
the
shifting
voltage
may be
reversed by the switch
S2. The
voltage
of
the
picture
shift
in
the
field
direction is
obtained from the
variable
provides the
e.h.t. for
the
dynamic
focus
cir-
.
.
.
_
cuit.
Separate
voltage
dividing
chains are
fit-
i
rçsïstor
VR
10
across
the
ZZV
11"e*.a"d
15
Set
ted
for
the
grid
2
and
focus
supplies,
the
lat-
ter
being
returned
to
a
negative supply
to
al-
low
for
negative focus voltages.
To
ensure
the best possible
resolution;
the
pic
ture
tube
is
su
lied
with the
maximum
allowab-
directly
to
the cold
end
of
the
field
deflec-
tion
coils.
It
should
be
noted
that
the
deflection coils
are
fitted
with
picture
shift
magnets.
At the
start
of
the adjustment procedure these
magnets
I
.d
2
t
95
1
Ita
of
700V.
This
ives
should
be
set
to
gero.
They
should
only
be used
8
QY"|
O
QP1
V0
Q
Q
a
of
75
to
::.::ïS@i.:"š
*e°";i2.:ï.t2:.::":;:.li"@:.:::
*ss
°f
the
1°W
Vide° Output
SuPp]y
V°1ta9e°
tÜ1S
used
to centre
the
raster
on
the
screen
cut-off
range
can be
provided
by
the negative
supply obtained
by
rectification
of
the voltage
across windings
1
and
6
of
the
line
output
transformer (also
used as
the
return
voltage
in
the focus
circuit).
The
picture
heater supply
is
obtained
from
a
winding
of
three turns
on
the
line
output transformer
core
opposite
to
the primary winding.
\-1
\-I
-
\-1
\./
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