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SECTION 2
OPERATING
INSTRUCTIONS
NOTE
The
Type
3A74
can
be
used
in either
the
X-axis
or Y-axis
plug-in
opening
of Tektronix Type
561-
Series,
567,
or RM567
oscilloscopes.
In the fol-
lowing
discussion
assume
that
the
Type
3A74
is
inserted
in the left-hand
(Y-axis)
opening
which
will
provide
vertical
deflection
with
crt
beam
blanking
of the channel
switching transient.
If the
the Type
3A74
is used with
a Type
565
or RM565
Dual-Beam
Oscilloscope, assume the unit is inserted
in
the
left-hand
vertical
opening.
FUNCTIONS
OF
FRONT-PANEL
CONTROLS
AND
CONNECTORS
Table 2-1
describes the functions of the front-panel con-
trols.
Since the four channels
are identical, the functions of
channel
1 control
and the inputs connector are described
in
the table.
Functions of the controls for the other channels are
identical.
Fig. 2-1 shows the front-panel layout.
TABLE
2-1
INPUT
CONNECTOR
BNC
Type
jack for coupling
input voltages to the chan-
nel 1 amplifier.
AC-GND-DC
Three-position
miniature
toggle
switch
provides
a
choice of ac or de coupling, or grounding the channel
] input
circuit without
grounding
the input connector.
VOLTS/DIV.
Nine-position
switch
to
select
the
calibrated
vertical
deflection
factors.
VAR. GAIN
Provides continuously variable attenuation between the
calibrated
deflection
factors,
and
extends
the attenua-
tion range to approximately
25 volts/div. This control
has
360°
rotation
and
it has a detent
position
for the
CAL.
(calibrated)
position.
DC BAL.
Screwdriver-adjustable
potentiometer
to
balance
the
amplifier de levels so the trace does not shift position
as the VAR. GAIN
control is varied.
GAIN ADJ.
Screwdriver-adjustable potentiometer to precisely adjust
the
deflection
factor
of the
channel.
(.02
VOLTS/DIV.
is the deflection
factor
normally
calibrated.)
POSITION
Potentiometer
to
provide
vertical
positioning
of
the
trace.
MODE
Three-position
switch
provides
the
following
choices:
'a normal display, an inverted display, or no display at
all. In the NORM.
position
the display
has the same
polarity as the input signal.
In the INV. position the
polarity of the signal
is inverted.
In the OFF
position
the channel
is turned off; during
muiti-trace operation
the channel
is excluded from the switching cycle.
TRIGGER
A push-pull switch which, when pulled, permits internal
triggering
on channel
1 signal only, regardless of the
channel
1 MODE
switch
settings.
When
the
switch
is
pushed
in with two or more
channels
''on", the time-
base
triggers
from
the composite
time-shared
vertical
signal.
With
only
one
channel
on,
the
channel
dis-
played
provides
the triggering
signal.
Plug-In Securing Knob
Permits
locking
the
Type
3A74
in
the
plug-in
com-
partment. (This knob is located at bottom center of the
plug-in
unit.)
CALIB.
Master gain control for adjusting the common
gain of
all channels.
Compensates
for differences
in ert deflec-
tion sensitivities.
NOTE
For plug-in
units S/N
156 and
up, including S/N
133
unit
(modified
out of sequence)
CALIB.
con-
trol
shaft
has
a shorter
length.
The
shorter
shaft
permits
the
front-panel
mounting
bushing
to
be
used
as a ground-connection
banana
jack.
CHOP.-ALT.
Two-position
toggle
switch
to select either alternate or
chopped
mode
of operation.
FIRST TIME
OPERATION
To place the Type 3A74 into operation for the first time,
rotate the plug-in securing
knob counterclockwise to move
the
latch
to
its fully
counterclockwise
unlatched
position.
Insert the unit in the left-hand
plug-in opening
of a Tek-
tronix Type
560-Series
oscilloscope
(except the Type 560).
Rotate the plug-in securing knob clockwise until hand tight.
1. Turn
on
the
oscilloscope
power.
Allow
about
2 to 3
minutes
warm-up
time
and
free
run
the
time
base
at 1
millisec/div. Set the front-panel
controls of the Type 3A74
to these settings.
AC-GND-DC
(all channels}
DC
VOLTS/DIV.
(all channels)
02
VAR.
GAIN
(all channels)
CAL.
2-1
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