charging
the
timing capacitance Ct. The positive-going
sweep
start
gate from
0864
turns
off
01024
and
the
timing
current
now begins
to
charge
the
timing capacitance.
Sawtooth Sweep Generator
01030
and
01036
compose a Miller Integrator circuit.
When
the
current
flow
through
the
Disconnect Amplifier
is
interrupted,
the
timing capacitance begins
to
charge
through
the
timing resistor.
The
timing resistor and
capacitance are selected by
the
A TIME/DIV switch
to
provide
the
various sweep rates listed on
the
instrument
front
panel. The
output
signal
at
the
collector
of
01036
is
a
negative-going
sawtooth
waveform.
Output Buffer Amplifier
The
Output
Buffer Amplifier stage
is
a common-base
amplifier with
the
signal current-driven
into
the
emitter.
It
provides
the
output
sawtooth
current
signal
to
the
Hori-
zontal Amplifier
and
provides a measure
of
isolation
between
the
Sawtooth
Generator
and
the
Horizontal
Amplifier. The HOR
IZ
DISPLAY switch
connects
to
this
stage
to
control
the
A
sawtooth
output
in
the
various
horizontal modes
of
operation.
In
the
A and A INTEN
modes
of
operation,
the
A sweep signal passes through
01038
to
the
Horizontal Amplifier. However,
in
the
MIX
and B DL Y'D modes,
-8
volts
is
connected
to
zener diode
VR1039
which sets
the
emitter
of
01038
at
about
-1.8
volts. This biases
01038
off, preventing
the
A
sawtooth
signal from passing
to
the
Horizontal Amplifier.
Sweep Start Amplifier
Just
before
the
sweep
starts
to
run
down,
the
levels
at
the
bases
of
01002
A and B are
approximately
equal. When
the
sweep starts
to
run
down,
the
base
of
01002B
goes
negative, which increases
the
forward bias on
CR1004.
This
in
turn decreases
the
forward bias on
CR1001,
which, very
shortly
after
the
start
of
the
sweep, becomes reverse biased
to
interrupt
the
current
through
01002A.
The circuit
remains in this condition until
after
the
sweep retrace
is
complete. When
the
circuit returns
to
quiescence,
01002A
again begins
to
conduct
through
R1024. This sets
the
current
through
01024,
which establishes
the
starting
point
for
the
sweep. The Sweep
Start
adjustment
sets
the
base
level
of
O1002A. This level
is
also
connected
to
the
base
of
O1062A
in
the
B Sweep
Generator
except
in
the
MIX
mode
of
operation. This ensures
that
B Sweep
starts
at
the
same
level
as
A Sweep.
Logic Multivibrator
01012
and
01014
compose
a multivibrator.
At
quies-
cence,
01014
is
conducting
and
01012
is
turned
off. When
I·:~
:J
®
i
.··;····
:-:=·:·::
Circuit
Description-465
the
sweep starts
to
run,
the
negative-going ramp
is
coupled
through
the
base
of
O1002B and
CR1004
to
the
cathode
of
CR1011.
CR1011 becomes forward biased and when
the
level
at
the
anode
of
CR
1011 falls
to
about
+4 volts O 1 O 12
conducts
and
01014
turns off. The multivibrator remains
in
this state until
the
sweep starts
to
retrace and
the
voltage
level
at
the
anode
of
CR
1011 rises above
about
+4.5 volts.
The resultant pulse
at
the
collector
of
01012
is
applied
to
Sweep Control
IC
U870
to
terminate
the
sweep. The pulse
at
the
collector of
01014
is
applied
to
the
A Sweep Z Axis
Logic Gate
to
blank
the
CRT
at
the
end
of
the
sweep.
B Sweep Generator Differences
There are three prime differences between
the
A and B
Sweep Generators. The B Sweep
Output
Buffer Amplifier
is
prevented from passing
the
B Sweep signal
to
the
Hori-
zontal Amplifier
in
the
A and A INTEN positions of
the
HORIZ DISPLAY switch. There
is
a transistor stage
connected
as
a
constant
current
source
in
the
emitter
circuit
of
O1062A
and B (corrects for
current
imbalances
side-to-side
in
01062
during
MIX
mode
operation).
The
Sweep
Start
Level
connected
to
the
base
of
O1062A
is
not
always a fixed
DC
level. During
MIX
mode
operation
the
A
Sweep
Sawtooth
signal
is
applied
to
the
base
of
the
amplifier. Now,
the
DC
level
at
which
the
B Sweep
Generator will
start
generating its
sawtooth
waveform
is
constantly
being changed by
the
A Sweep
sawtooth.
The
output
waveform from
the
B
Sweep
Generator
takes
the
form
of
a composite
sawtooth
waveform, with
the
first and
last parts occurring
at
a rate
determined
by
the
A Sweep
Generator and
the
middle
part
occurring
at
a rate deter-
mined by
the
B Sweep Generator.
General
SWEEP
AND
Z
AXIS
LOGIC
CIRCUIT
The
Sweep And Z Axis Logic Circuit derives
the
logic
levels necessary
to
control
the
sequence
of
events associated
with sweep generation and CRT unblanking.
The
+A and
+B
GATE signals are also generated
in
this circuit. Positive
logic terminologies and symbologies will be used in
the
following explanation
of
circuit
operation.
A schematic of
this circuit
is
shown on diagram 8
at
the
rear
of
this
manual.
A Sweep Gate
0862
and
0864
compose
the
A Sweep Gate Circuit.
They form an
emitter
coupled stage where only one
transistor can be conducting
at
any
time.
The
input
signal
to
the
stage
is
the
positive-going trigger signal from
the
A
Fire Trigger TD in
the
A Trigger
Generator
Circuit. The
For
Servloe
Manuele
MAURITRON
SERVICES
8
Cherry
Tree
Road,
Chlnnor
Oxfordshire,
OX9
4QY,
Tel
(01844)
351694
Fax(01844)352554
email:-
maurilronOdial.pipex.com
3-11
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