Theory of Operation-2225 Service
applied to
U480B
pin
7
rises to a level that will cause
the Trigger output gate
U480B
pin
3
to switch.
Precise TV field synchronization is obtained as a re-
sult of this filtering action. The Trigger signal output
will be the inverse of the filtered signal appearing at
U480B
pin
7.
SWEEP AND SWEEP GENERATOR LOGIC
The Sweep Logic circuitry and the Sweep Generator
circuitry, shown on diagrams
4
and
5
respectively,
produce a linear voltage ramp that drives the
Horizontal Preamplifier. The Sweep Logic circuit also
produces signals that are used to generate correct
timing of the crt unblanking and intensity levels used
for viewing the display. See Figure
3-3
for the block
diagram of the Sweep Generator and Logic circuitry.
Miller Sweep Generator
The Miller Sweep Generator (diagram
5)
produces a
linear voltage ramp that drives the Horizontal Ampli-
fier. It produces the ramp voltage by maintaining a
constant current through timing capacitors, causing
a linear voltage rise across them as they charge.
Field-effect transistors
Q704A
and
Q704B
are
matched devices with
Q704B
acting as the current
source for
Q704A.
Since the gate and source of
Q704B
are connected together, the source current
available to
Q704A
is just enough so that there is no
voltage drop across the gate-source junction of
Q704A.
When the sweep is not running,
Q701
is biased on,
holding the selected timing capacitors in a dis-
charged state. The low impedance of
(2701
in the
feedback path holds the Miller Sweep output near
ground potential. The voltage across
Q701,
in
addition to the base-emitter voltage of
(2706,
prevents
0706
from becoming saturated.
Figure
3-3.
Block diagram of the Sweep Generator and Logic circuit.
Scans
by
ARTEK
MEDIA
-
xi-
FROM
HORIZONTAL
ALT
-
MODE
5601
ALT/MAG
CIRCUIT
U510A
U515A
0514
FROM
THE
TRIGGER SIGNALS
-
TRIGGER
i
CIRCUITRY
MAG
-
-
-
C
AUTO
BASELINE
U520D
U570A
U570B
U5800
SINGLE
SWEEP
U550C
-
-
TO
HORIZONTAL
AMPLIFIER
-
END-OF-SWEEP
U560E
6299-28
SWEEP
LOGIC
U520A
U520B
c
c
SWEEP
GENERATOR
0701.
0704A
07040. 0706
U715
I
U520C HOLDOFF
U530B U5000
To Next Page
Loading...