Servicing
Information— SC
501
SWEEP
AND
HORIZONTAL AMP CIRCUIT DESCRIPTION
Trigger. Integrated circuit
U200
is a
combination
Trigger/Sweep Generator.
The Trigger
portion (input pin
13)
derives
trigger pulses
from
a
sample of the Vertical
Amplifier signal, or
from
an
external signal
applied
to
the
EXT
TRIG
pin jack. CR200 and CR201
limit the amplitude
swing
of
the trigger
signals.
C204
is the
differentiating
capacitor
for
the
trigger pulses. LEVEL/SLOPE control is
provided
by a
voltage
applied
to
pin 14 from R210. No
trigger signals can start
the sweep
generator system until
sweep
hold-off period has been
completed. The sweep
hold-off
F>eriods
(pin
3)
are
determined by the RC time
constants of
R215, C218,
and
C220.
The
timing period for
the
AUTO
triggering mode is
determined
by
the
time
constant
of R205 and C205
if
no
voltage is
applied
to
pin
10
through
S205.
For
normal
triggering,
approximately
—6
V
is
applied
to
pin 10 through S205.
Sweep
Generator. The Sweep
Generator
portion
of
U200
produces two output
signals; the sweep ramp voltage
on pin
4 and
crt
unblanking gate on
pin 16.
The
sweep is
generated
by
a feedback
operational
amplifier integrating
circuit. The slope of the ramp
is controlled by
fixed
RC
time
constants selected
by
the Tlme/div
pushbuttons.
CR215
provides
a
low
impedance discharge path
for
the
sweep
capacitors. Sweep
length is
controlled
by a
voltage
applied
to
pin
6
from R212
(Sweep Adjust).
Sweep
VARIABLE
control, R225,
controls
the charging
current
to
the
sweep
(integrating)
capacitors
and when
varied changes
the slope of the ramp at
pin 4.
Horizontal Amplifier.
Sweep
ramp voltages
or
signals
from the
EXT HORIZ pin jack
are applied
to the base of
Q252.
The circuit containing
Q252 and
Q270 is
an
emitter-coupled paraphase
amplifier
with
a
horizontal
POSITION
control voltage applied
to
the
base of
0270
and
R275.
In
the
magnified
mode,
emitter degeneration is
reduced, resulting in
a X5
increase
in
gain.
Clamping diodes,
CR280
and
CR282
limit
the positive
excursions of the
signals
at the bases
of
Q285
and
0290 to about
—3
V as set
by
Zener diode,
VR280.
Push-pull signals
are developed
at
the collectors of
Q285
and
0290 to drive the horizontal
deflection plates of the crt.
Ramp Out. The
Ramp
Out
feedback
amplifier circuit,
0240 and
0250,
produces
a
zero
to
-HO
V
ramp or an
amplified and
inverted version of signals from the EXT
HORIZ
pin jack to
the rear connector pins.
The feedback
arrangement
allows the
emitter of
0250 to
be
set
to a
zero
volt dc
level, and produces a
low
output
impedance without
causing 0240 to go
into saturation.
External Horizontal Amplifier.
The External Horizontal
Amplifier circuit is an operational amplifier configuration,
U310,
fed
by
buffer amplifier
0305.
The gain
of U310 is
fixed
at about
six
by
R310 and R305.
R300
controls the
external
signal amplitude
to
the
gate of
O305A.
To Next Page
Loading...
Need help?
General
