Tektronix 7A18 User manual

Tektronix, Inc
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Phone
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OPTION INFORMATION
REV . JUNE
1974
CHANGE
INFORMATION
7A18/7A18N
Abbreviations and symbols used in this manual are
based on
or taken directly from IEEE Standard 260
"Standard
Symbols for Units", MIL-STD-12B and other
standards of .
the electronics
industry
.
Change information, if any, is
located at the rear of this manual .
SECTION 1
SPECIFICATION Page
Introduction
1-1
Electrical Characteristics 1-1
7A18 And Mainframe Frequency
Response 1-3
Environmental Characteristics 1-3
Physical Characteristics 1-3
SECTION 2 OPERATING INSTRUCTIONS
Installation 2-1
Front
Panel Controls and Connectors 2-1
General Operating
Information 2-2
Basic Applications 2-4
SECTION 3 CIRCUIT DESCRIPTION
Introduction 3-1
Block Diagram Description
3-1
Detailed Circuit Description
3-1
SECTION4 MAINTENANCE
Preventive Maintenance 4-1
Troubleshooting
4-1
Replacement
Parts 4-3
Component
Replacement 4-4
SECTION 5 CALIBRATION
Recalibration Interval 5-1
Test Equipment Required
5-1
Part
I - .-
Performance Check 5-3
Part II -- Adjustment
5-7
SECTION
6 ELECTRICAL
PARTS LIST
Abbreviations
and Symbols
Parts
Ordering Information
SECTION 7
DIAGRAMS AND
CIRCUIT BOARD
ILLUSTRATIONS
Symbols and Reference Designators
Voltage and Waveform Conditions
SECTION8 MECHANICAL
PAR'I'S LIST
Mechanical Parts
List Information
Index
of Mechanical Parts Illustrations
Mechanical Parts
List
Accessories

7A18/7A18N
Fig . 1-1 .
7A18 and 7A18N
Amplifier .

Introduction
The
7A18 and 7A18N Dual Trace Amplifier
plug-in
units are designed
for use with Tektronix 7000-Series
Oscilloscopes
. The 7A18 and 7A18N are electrically iden-
tical except
that readout encoding capabilities and
an
"IDENTIFY"
function are provided only in the 7A18 . All
references
made to the 7A18 apply equally to the 7A18N
unless
otherwise noted . The 7A18 is a dual-channel,
medium-bandwidth
amplifier . Internal gain and
compensa-
tion
circuits are automatically switched to
correspond to
Deflection Factor
GAIN
Deflection Factor Accuracy
Characteristic
Calibrated Range
Uncalibrated
(VARIABLE)
Frequency Response
System Dependent
(8 div reference signal)
Upper Bandwidth
DC (Direct) Coupled
Lower Bandwidth
AC (Capacitive) Coupled
With
10X Probe
Change information, if
any, affecting this section will be found
at the rear of the manual .
Performance Requirement
5 mV/Div to 5 V/Div ; ten
steps in a 1,
2, 5 sequence .
Within 2% with GAIN adjusted
at
0 . mV / D i v
. .
._ ._
. . .__ . ._ .
Continuously
variable between calibrated
steps ;
extends deflection factor to at
least 12 .5
V/Div .
See Table A
10 Hertz or less
1 Hertz
or less
TABLE
1-1
ELECTRICAL
the setting of the VOLTS/DIV switch .
Channel 2 can be
inverted for differential measurements
. The 7A18 can be
operated
in any plug-in compartment
of the 7000-Series
Oscilloscopes
.
The following electrical characteristics are valid over the
stated environmental range for instruments calibrated at an
ambient temperature of +20 ° C to
+30
° C, and after a five
minute warmup unless otherwise noted,
series
oscilloscopes .
7A18/7A18N
Permits adjustment
of deflection factor
for calibrated
operation with all 7000-

Specification-7A18/7A18N
TABLE
1-1 (cont)
Characteristic
Maximum
InputVoltage
DC Coupled
AC Coupled
Channel
Isolation
Input
R and C
Resistance
Capacitance
RC Product
m . .
Displayed Noise
(Tangentially Measured)
Overdrive Recovery Time
Common
Mode Rejection
DC
Drift
Display Modes
Drift with Time (ambient
temperature and line voltage
constant)
Drift with Temperature
(line voltage constant)
Time Delay between Channels
Performance Requirement
50 :1 display
ratio up to 50
megahertz
.
1 MQ±2%~
- Approximately 20 .0 pf
At least 10 :1 up
to 50 megahertz .
Channel
1 only .
Dual-trace, alternate
between channels .
Added algebraically .
Dual-trace chopped
between channels .
Channel
2 only .
Supplemental, Information
250
volts, (DC+ Peak AC) ; AC com-
ponent500 volts peak-to-peak maxi-
mum, one kilohertz or less .
500 volts, (DC
+
Peak AC) ; AC compo-
nent 500 volts peak-to-peak
maxi-
mum, one kilohertz or
less .
Within
:,_
1% between
all deflection
-"
factors .
300
microvolts or less at 5 mV/Div in
7000-Series
Oscilloscope .
0 .1 ms or less to recover
to within one
division after the
removal of an over-
drive signal of up
to +75 divisions or
---75 divisions
regardless of overdrive
signal duration
.
0.02 division
or less in anyone minute,
after one
hour warmup .
No more than
0 .01 division per degree C .
700
picoseconds or less .

Cha,~~o,puo
Trigger source Selection
Size
Weight
With 7700 SeHes
75 MHz
Performance Requirement
:7-
Channel l only .
Follows DISPLAY MODE selection .
TABLE 1-1 (cont)
TABLEA
7A18 AND
MAINFRAME
FREOUENCY RESPONSE
60 MHz
TABLE
1-2
ENVIRONMENTAL
CHARACTERISTIC
Refer to
We Specification for
the associated oscilloscope .
TABLE
1-3
PHYD!CAL
Fits all 7000-series
plug-in compartments .
2 Pounds 10 Ounces
(1 .4 kilograms)
Specification-7A18/7Al8N
With 7400S=,ip
50 MHz

General
To effectively use the 7A18, the operation and capabili-
ties of the instrument must be known . This section des-
cribes front-panel control functions, general information on
signal input connections, and other subjects that pertain to
various measurement applications .
Installation
SECTION 2
OPERATING INSTRUCTIONS
Change
information, if any, affecting this section will be found at the rear of the manual .
The 7A18 is calibrated and ready for use as received . It
can be installed in any compartment of Tektronix 7000-
Series oscilloscopes, but is intended for principal use in
vertical plug-in compartments . To install, align the upper
and lower rails of the 7A18 with the oscilloscope tracks and
fully insert it . The front will be flush with the front of the
oscilloscope when the 7A18 is fully inserted, and the latch
at the bottom-left corner of the 7A18 will be in place
against the front panel .
To remove the 7A18,
pull on the latch (which is
inscribed with the unit identification
"7A18" or "7A18N")
and the
7A18
will
unlatch
.
Continue pulling on the latch to
slide
the 7A18 out of the oscilloscope .
FRONT PANEL CONTROLS
AND CONNECTORS
The following descriptions apply to the controls and
connectors of both Input Amplifier channels when appli-
cable . See Fig . 2-1 .
Input Connector

Provides signal connection to the
channel .
AC-GND-DC

Selects signal input coupling mode .
AC-The AC component of the
sig-
nal is coupled to the amplifier
input while the DC component
is blocked
.
Fig .
2-1 . Front-panel controls and connectors . (7A18shown .)
POSITION
GND-Grounds the amplifier input
while maintaining the same load
for the input signal . Provides a
charge path for the AC coupling

IDENTIFY
capacitor to precharge the input
circuit before switching the
input to AC .
(7A18 only)
7A18/7A18N
DC-Both AC and DC components
of the signal are coupled to the
amplifier input .
Controls position of the
trace . Posi-
tioning of the trace
in the "ADD"
Display Mode is controlled
by CH 1
POSITION control
only
.
Deflects trace about 0 .2 division for
trace identification . In instruments
with readout, also replaces readout
with the word "IDENTIFY" .

Operating Instructions-7A18/7A181\1
VOLTS/DIV

Selects calibrated deflection factors
from
5 mV/Div to 5 V/Div ; ten
steps in a 1-2-5
sequence .
VARIABLE

Provides continuously variable un
(VOL1 - S/DIV)

calibrated settings between cali-
brated steps . Extends the deflection
factor range to 12 .5 volts/division
or more .
GAIN Adjustment

When the VARIABLE control is
pushed in, it becomes a front-panel
screw-driver adjustment for cali-
bration of deflection factor .
DISPLAY MODE

Selects
one
of the following modes
of operation :
2-2
CH 1-A single-trace display of the
signal applied to Channel 1 .
ALT---A
dual-trace
display
of
the
signal
applied to both channels .
-T- he channels are alternately dis-
played, and switching occurs at
the end of each time-base
sweep .
ADD-Algebraically adds the signals
applied to the CH 1 and CH 2
input connectors, and the
algebraic sum is displayed on
the CRT . The CH 2 POLARITY
switch allows the display to be
CH 1 + CH 2 or CH 1 - CH 2 .
Position of the trace in this dis-
play mode is controlled by CH 1
POSITION control only .
CHOP---A dual-trace display of the
signals applied to both channels .
Thetwo channels time-share the
sweep as determined by the in-
dicator oscilloscope .
CH 2--A single-trace display of the
signal applied to CH 2 .
TRIGGER SOURCE

Selects source of the trigger signal .
The trigger signals provide internal
triggering for the oscilloscope time-
base units .
CH

1- I nternal

triggering

signal
obtained from signal applied to
CH 1 .
MODE--Internal trigger signal auto-
matically follows DISPLAY
MODE selection . In ADD or
CHOP display
modes, the trigger
signal is the algebraic
sum of CH
1 and CH 2 trigger .
CH 2---Internal trigger signal
obtained from signal applied
to
CH 2 .
CH 2 POLARITY

Provides means of inverting
the CH
2 display .
Introduction
Signal Connections
+
-UP--A positive-going signal at
the
CH 2 input connector
deflects
the CRT display upward .
INVERT--A
positive-going signal at
the CH 2
input connector de-
flects the
CRT display down-
ward .
GENERAL OPERATINGINFORMATION
For single-trace operation, either of the two identical
amplifier channels can be used independently by setting the
DISPLAY MODE and TRIGGER SOURCE switches to CH
1 or CH 2 and connecting the signal to be observed to the
appropriate input . In the discussions to follow, single-trace
operations using CH 1 only apply equally to CH 2 only .
In general, probes offer the most convenient means of
connecting a signal to the input of the 7A18 . A 10X atten-
uator probe offers a high input impedance and allows the
circuit under test to perform very close to normal operating
conditions .
The Tektronix P6053A probe, with its readout
cod~ng
ring, was designed specifically for use with Tektronix
7A-
series amplifier units equipped with readout . The readout
coding ring on the probe connects to a circuit in the ampli-
fier unit which automatically corrects the readout displayed
on the CRT to the actual deflection factor at the tip of the
probe being used . For probes to be used with amplifier
units without readout, see the Tektronix, Inc . catalog .
Vertical
Gain Check and Adjustment
To
check
the gain of either channel, set the VOLTS/DIV
switch to 10 mV and connect
40
mV,
1
kHz
signal from the
oscilloscope calibrator to
the input connector of the chan-
nel being checked . The vertical
deflection should be exactly
four divisions . If not, adjust the front-panel GAIN
for
exactly four divisions of deflection .
The GAIN adjustment
is engaged by pressing
in the GAIN control knob and turn-
ing the knob with a narrow-blade
screwdriver (see Front

Panel Controls and
Connectors) . Turn the knob clockwise,
then counterclockwise,
until the GAIN control is engaged .
When the GAIN control
is engaged, the vertical deflection
will change as the knob is turned .
"Turn the GAIN control
knob with the screwdriver until the
deflection is set to
exactly four divisions, then remove the screwdriver .
Input Coupling
The Channel 1 and Channel 2
coupling (AC-GND-DC)
switches allow a
choice of input coupling methods .
The
type of display desired and
the applied signal will
determine
the coupling to use .
The
DC coupling position must be used
to display the
DC component
of the signal . It must also be
used to display
AC signals below about
30 hertz (ten hertz with a
10X
probe) and square
waves with low-frequency
components as
these signals are
attenuated in the AC position .
In the AC coupling
position, the DC component
of the
signal is blocked by a
capacitor in the input circuit . The
AC
coupling position provides
the best display of signals with
a
DC component much larger
than the AC components . The
precharge feature should
be used with large DC inputs . To
use this feature, first
set the coupling to GND . Connect the
probe to the circuit and
wait about two seconds for the
coupling capacitor to charge
. Then set the coupling to AC .
The GND position provides a
ground reference at the
input of the amplifier
without externally grounding the
input connectors . However, the signals
connected to the
inputs
are not grounded, and the same DC
load is presented
to the
signal source .
VOLTS/DIV and VARIABLE
Controls
The amount of vertical deflection
produced by a signal is
determined by the signal amplitude, the
attenuation factor
of the probe, the setting of the VOLTS/DIV switch, and
the setting of the VARIABLE control . Calibration deflec-
tion factors indicated by the settings of the
VOLTS/DIV
switch apply only when the VARIABLE
control is in the
calibrated (CAL IN) position .
The VARIABLE
control provides variable, uncalibrated
settings between
the calibrated steps of the VOLTS/DIV
switch . With the VARIABLE
control fully counterclock-
wise and the VOLTS/DIV set
to 5 volts/div the uncali-
brated vertical deflection factor is
extended to at least 12 .5
volts/division . By applying a calibrated
voltage source to
the input connector, any specific
deflection factor can be
set within the range of the VARIABLE
control .
REV . APR
1974
CH 2
POLARITY Switch
DISPLAY MODE Switch
Operating Instructions---7A18/7A18N
The
CH 2 POLARITY
switch may be used to invert the
displayed waveform
of the signal applied to the CH 2 input .
This is particularly useful
in added operation of the 7A18
when differential
measurements are to be made . The CH 2
POLARITY switch has two
positions, +UP and INVERT . In
the +UP position,
the displayed waveform will have the
same polarity as the applied
signal and a positive DC voltage
will move the CRT trace
up . In the INVERT position, a
positive-going waveform
at the CH 2 input will be displayed
on the CRT in
inverted form and a positive DC voltage will
move the trace down .
For single-trace operation, apply the signal either to the
CH 1 input or the CH 2 input and set the DISPLAY MODE
switch to the corresponding position : CH 1 or CH 2 .
To display a signal in one channel independently when a
signal is also applied to the other channel, simply select the
desired
channel by setting the DISPLAY MODE switch to
the
appropriate CH 1 or CH 2 position .
Alternate Mode . The ALT position of
the DISPLAY
MODE switch produces a display which
alternates between
channel 1 and channel 2 with each sweep
on the CRT .
Although the ALT mode can be used at all sweep rates,
the
CHOP mode provides a more satisfactory display at sweep
rates below
about 0 .2 millisecond/division .
At slow sweep
rates alternate mode switching becomes visually per-
ceptible .
Add
Mode . The ADD position of the DISPLAY MODE
switch
can be
used to display the sum or difference of two
signals,
for common-mode rejection to remove an undesired
signal, or for DC
offset (applying a DC voltage to one
channel to offset the DC
component of a signal on the
other channel) . The overall
deflection factor in the ADD
mode with both VOLTS/DIV
switches set to the same
position is the deflection factor
indicated by either
VOLTS/DIV switch .
However, if the CH 1 and CH 2
VOLTS/DIV switches
are set to different deflection factors,
the resultant amplitude
is difficult to determine from the
CRT display . In this case,
the voltage amplitude of the
resultant display can be determined
accurately only if the
amplitude of the signal
applied to one channel is known . In
the ADD mode,
positioning of the trace is controlled by the
channel 1 POSITION
control only .
Chop Mode . The CHOP
position of the DISPLAY
MODE switch produces a display
which is electronically
switched between channels at
approximately a 500 kilo-
hertz rate (controlled by mainframe) .
In general the CHOP
mode provides the best display
at sweep rates slower than
2-3