Operating instructions
Q204
prevent
the
sweep
disable
out
pulse
at
U220-pin
17
from
falling
LO
until
the timing
capacitors
have
discharged
.
Transistors
Q212
and
Q214
and
front-panel
HOLD
OFF
control
R210
provide
variable
current
to
the
timing
compo-
nents
to
change
the
hold
off
time
period
.
Lockout
Buffer
Amplifier
A
lockout
pulse
(HI)
may
be
initiated
at
interface
connect-
or
pin
B8
by
mainframe
switching
functions
.
A
HI
level,
coupled
from
interface
connector
B8
through
the
Lockout
Buffer
Amplifier
(Q201,
Q202,
and
Q206)
to
the
lockout
input
at
U220-pin
18,
initiates
a
sweep
disable
pulse
at
U220-pin
17
thereby
disabling
the
sweep
.
The
lockout
pulse
(H
I) is
also
applied
through
Q358
(diagram
4) to
the
hold
off
start
input
at
U220-pin
16
to
enable
the
hold
off
cycle
.
Hold
Off
Output
Amplifier
The
Hold
Off
Output
Amplifier
inverts
and
amplifies
the
hold
off
signal
from
U220-pin 10
for
use
by
the
mainframe
.
Transistor
Q272
inverts
the
hold
off
signal
from U220-pin
10
to
provide
a
H
I
level
when
hold
off
is
present
.
The
in-
verted
signal
is
coupled through
emitter
follower
Q274
to
interface
connector
B4
.
The
Sweep
Generator
produces
a
linear
ramp
waveform
for
the
mainframe
when
gated
by the
Trigger
Generator
.
A
sweep
gate
(unblanking)
is
also
generated
in this
circuit
block
.
The
linear
sweep
ramp
waveform
is
produced
by
charging
a
capacitor
from
a
constant
current
source
.
The
slope
of
the
ramp
determines
the
sweep
rate
of
the
displayed
trace
.
A
block
diagram
of
the
Sweep
Generator
is
shown
in
Figure 3-6
.
Timing
Current
Source
The
Timing
Current
Source
stages
generate
a
constant
cur-
rent
for
the
Ramp
Generator
stages
(see
Figure
3-6)
.
A
Reference
Voltage Source
is
established
by
the
+50
volt
supply
and
R710,
R711,
R717,
and
R705
(front-panel
SWP
CAL
adjustment)
.
The
reference voltage
is
applied
to
the
Source Current
Gen-
erator
stage
.
Operational
amplifier
U722
provides
unity
voltage
gain
and
low output
impedance
.
The
output
of
U722
is
connected
through
the
base-emitter junction
of
Q732
to
the
Timing
Resistors
(R741
through
R749)
.
Tim-
ing
current
is
the
result
of
the
voltage
drop
across
the
REV
.
A,
APR
.
1976
SWEEP
GENERATOR
4O
Theory
of
Operation-71380
Timing
Resistors
and
flows
through the
collector
of
Q732
to
the
Ramp
Generator
stages
.
Ramp
Generator
The
Ramp
Generator
stages
produce
a
linear
positive-going
ramp
for
the
Output
Preamplifier
and
Sweep
Gate
Genera-
tor
stages
.
Refer
to
Figure 3-6
.
Upon
the
arrival
of
a
HI-level
sweep
start
gate
at
the
Cur-
rent
Switch
stage,
Q322
turns
on
and
Q324
turns
off
.
The
source
current
from
Q732
charges
the
Timing
Capacitors
(C332,
C334,C336)
in
a
positive
ramp
.
Field
effect
transis-
tors
Q334A,
Q334B,
and
transistor
Q338
form a
unity-gain
Ramp
Voltage
Follower
for the
sweep
ramp
.
The
output
of
Q338
is
connected to
the
Horizontal
Preamplifier,
Sweep
Stop
Comparator,
and
Baseline
Stabilizer
stages
.
When
the
sweep
start
gate
is
LO,
Q322
turns
off
and
Q324
turns
on
causing
the
Timing
Capacitors
(C332,
C334,
and
C336)
to
discharge
.
The
Baseline
Stabilizer
stage
(Q304,
Q314)
maintains
a
constant
level
from
which
the
ramp
be-
gins
.
The
output
of
Q338
is
compared
(by
way
of
Q304A)
with
the
reference
level
at
the
base of
Q304B
.
If
the output
of
Q338
is
less
than
the
reference,
Q314
will
charge the
timing
capacitors
through
CR323
until
the
output
and
re-
ference
voltages
are
equal
.
If
the
output
of
Q338
is
greater
than
the
reference,
Q314
conducts
more
and
CR323
con-
ducts
less
causing
the
Timing
Capacitors
to
discharge
through
Q324
and
R322
.
When
the
output
and
reference
voltages
are
equal,
the
current
through
CR323
and
Q732
equals
the
current
through
Q423
.
Output
Preamplifier
The
Output
Preamplifier
stages
connect
the
differential
sweep
signal
to
the
mainframe
and
provide
an
offset
voltage
for
trace
positioning
.
Provisions
are
made
in
these
stages
for
sweep
magnification,
and
a
negative-going
sawtooth
signal
is
supplied
to
the
mainframe
for
sawtooth output and
special
plug-in unit
functions
.
Refer
to
Figure
3-6
.
The
sweep
ramp
voltage
from
Q338
is
coupled
to
the
Hori-
zontal
Preamplifier
stage
at
the
base of
Q424
.
Transistors
Q424
and
Q434
form
a
single-ended to
push-pull
converter
with
Q428
and
Q438
as
current
follower
stages
for
the
push-pull
signal
.
Output
drivers
Q448
and
Q458
provide
final
amplification
and connect
the
sweep
signal
to
the
mainframe
.
The
MAG
switch,
S435,
increases
the
Horizontal
Preampli-
fier
gain
ten
times
by
connecting
R431
and
R430
in
parallel
with
R442
.
3-
1 1