Tektronix 7A18 User manual

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INSTRUCTION
MAN UAL
Tektronix, Inc, @ P. O. Box 500 @ Beaverton, Oregon 97005 @ Phone [phone] @ Cables: Tektronix
070-1126-01 1271

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SECTION 1
SECTION 2
SECTION 3
SECTION 4
SECTION 5
©1
7A18/7A18N
TABLE OF CONTENTS
SPECIFICATION
Introduction
Electrical Characteristics
7A18 And Mainframe Frequency
Response
Environmental Characteristics
Physical Characteristics
OPERATING INSTRUCTIONS
Installation
Front Panel Controls and Connectors
General Operating Information
Basic Applications
CIRCUIT DESCRIPTION
Introduction
Block Diagram Description
Detailed Circuit Description
MAINTENANCE
Preventive Maintenance
Troubleshooting
Replacement Parts
Component Replacement
CALIBRATION
Recalibration Interval
Test Equipment Required
Part | — Performance Check
Part I] — Adjustment
Page
1
4 SECTIONG
SECTION 7
SECTION 8
3-1
3-1
3-1
4-1
4-1
OPTION INFORMATION
ELECTRICAL PARTS LIST
Abbreviations and Symbols
Parts Ordering Information
DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
Symbols and Reference Designators
Voltage and Waveform Conditions
MECHANICAL PARTS LIST
Mechanical Parts List Information
Index of Mechanical Parts Illustrations
Mechanical Parts List
Accessories
4-3 CHANGE INFORMATION
4-4
Abbreviations and symbols used in this manual are based on
5-1 or taken directly from IEEE Standard 260 “Standard
5-1 Symbols for Units’, MIL-STD-12B and other standards of
5-3 the electronics industry. Change information, if any, is
5-7 located at the rear of this manual.
REV. JUNE 1974

7A18/7A18N
Fig.
1-1.
7A18
and
7A18N
Amplifier.
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7A18/7A18N
SECTION 1
SPECIFICATION
Change information, if any, affecting this section will be found at the rear of the manual.
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
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.
TABLE 1-1
ELECTRICAL
Characteristic
Performance Requirement
Supplemental Information
Deflection Factor
Calibrated Range
2, 5 sequence.
5 mV/Div to 5 V/Div; ten steps ina 1,
Deflection Factor Accuracy
10 mV/Div.
Within 2% with GAIN adjusted at
Uncalibrated
(VARIABLE)
least 12.5 V/Div.
Continuously variable between calibrated
steps; extends deflection factor to at
GAIN
Permits adjustment of deflection factor
for calibrated operation with all 7000-
series oscilloscopes.
Frequency Response
System Dependent
(8 div reference signal)
Upper Bandwidth
DC (Direct) Coupled See Table A
Lower Bandwidth 10 Hertz or less
AC (Capacitive) Coupled
With 10X Probe 1 Hertz or less
1-1

Specification—7A18/7A18N
TABLE 1-1 (cont)
Characteristic
Performance Requirement
Supplemental Information
Maximum Input Voltage
DC Coupled 250 volts, (DC + Peak AC); AC com-
ponent 500 volts peak-to-peak maxi-
mum, one kilohertz or less.
AC Coupled 500 volts, (DC + Peak AC); AC compo-
nent 500 volts peak-to-peak maxi-
mum, one kilohertz or less.
Channel Isolation 50:1 display ratio up to 50
megahertz.
Input R and C
Resistance
1 MQ + 2%
Capacitance Approximately 20.0 pf
RC Product
Within +1% between all deflection
factors.
Displayed Noise
(Tangentially Measured)
300 microvolts or less at 5 mV/Div in
7000-Series Oscilloscope.
Overdrive Recovery Time
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.
Common Mode Rejection
Ratio
At least 10:1 up to 50 megahertz.
DC Drift
Drift with Time (ambient
temperature and line voltage
constant)
0.02 division or less in any one minute,
after one hour warmup.
Drift with Temperature
(line voltage constant)
No more than 0.01 division per degree C.
Time Delay between Channels
700 picoseconds or less.
Display Modes
Channel 1 only.
Dual-trace, alternate between channels.
Added algebraically.
Dual-trace chopped between channels.
Channel 2 only.
1-2

TABLE 1-1 (cont)
Specification—7A18/7A18N
Characteristic Performance Requirement
Supplemental Information
Trigger source Selection
Channel 1 only.
Follows DISPLAY MODE selection.
Channel 2 only.
TABLE A
7A18 AND MAINFRAME
FREQUENCY RESPONSE
With 7700 Series
75 MHz
With 7500 Series
60 MHz
With 7400 Series
50 MHz
TABLE 1-2
ENVIRONMENTAL CHARACTERISTIC
Refer to the Specification for the associated oscilloscope.
oy
TABLE 1-3
PHYSICAL
Size
Fits all 7000-series plug-in compartments.
Weight
2 Pounds 10 Ounces (1.4 kilograms)
1-3

NOTES

7A18/7A18N
SECTION 2
OPERATING INSTRUCTIONS
Change
information,
if
any,
affecting
this
section
will
be
found
at
the
rear
of
the
manual.
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
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 7A 18 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.
Provides signal connection to the
channel.
Input Connector
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.
GND—Grounds the amplifier input
while maintaining the same load
for the input signal. Provides a
charge path for the AC coupling
capacitor to precharge the input
circuit before switching the
input to AC,
Fig. 2-1. Front-panel controls and connectors. (7A18 shown.)
DC-—Both AC and DC components
of the signal are coupled to the
amplifier input.
POSITION Controls position of the trace. Posi-
tioning of the trace in the “ADD”
Display Mode is controlled by CH 1
POSITION control only.
IDENTIFY Deflects trace about 0.2 division for
(7A 18 only) trace identification. In instruments
with readout, also replaces readout
with the word “IDENTIFY”.
2-1

Operating Instructions—7A18/7A18N
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-
(VOLTS/DIV) calibrated settings between cali-
brated steps. Extends the deflection
factor range to 12.5 volts/division
or more.
When the VARIABLE control is
pushed in, it becomes a front-panel
screw-driver adjustment for cali-
bration of deflection factor.
GAIN Adjustment
DISPLAY MODE Selects one of the following modes
of operation:
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.
The 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.
The two 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—Internal triggering signal
obtained from signal applied to
CH 1.
MODE-~—Internal trigger signal auto-
matically follows DISPLAY
MODE selection. In ADD or
2-2
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.
+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 OPERATING INFORMATION
Introduction
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.
Signal Connections
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 coding
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
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