Tektronix 7A24 User manual

TEKTRONIX®
INSTRUCTION MANUAL
Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97005 Serial Number
070-1485-00 873

WARRANTY
All Tektronix instruments are warranted against defective
materials and workmanship for one year.
Additionally, all Tektronix Computer Display Terminals
and related computer peripheral equipment are fully
warranted against ANY trouble for the first 90 days. Any
equipment trouble occurring to your Tektronix computer
terminal or related products during the 90 day period will
be repaired by Tektronix personnel at no charge.
Questions regarding warranty should be discussed with your
Applications Engineer.
Specifications and price change privileges reserved.
Copyright ©1973 by Tektronix, Inc., Beaverton, Oregon.
Printed in the Unit^ States of America. All rights reserved.
Contents of this publication may not be reproduced in any
form without permission of Tektronix, Inc.
U.S.A. and foreign Tektronix products covered by U.S. and
foreign patents and/or patents pending.
TEKTRONIX is aregistered trademark of Tektronix, Inc.

TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS iii
LIST OF TABLES iii
SECTION 1OPERATING INSTRUCTIONS
PRELIMINARY INFORMATION 1-1
Installation 1-1
GENERAL OPERATING INFORMATION 1-1
Introduction 1-1
Signal Connections 1-1
Vertical Gain Check and Adjustment 1-1
input Coupling 1-1
Input Protection Fuse 1-3
VOLTS/DIV and VARIABLE Controls 1-3
CH 2POLARITY Switch 1-3
DISPLAY MODE Switch 1-3
TRIGGER SOURCE Switch 1-3
Trace identification 1-4
BASIC APPLICATIONS 1-4
General 1-4
Peak-to-Peak Voltage Measurements 1-4
Instantaneous Voltage Measurements 1-5
Comparison Measurements 1-5
Dual Trace Phase Difference Measurements 1-6
High Resolution Phase Measurements 1-7
Common Mode Rejection 1-7
SECTION 2SPECIFICATION
introduction 2-1
Electrical 2-1
Environmental 2-2
Physical 2-2
SECTION 3THEORY OF OPERATION
INTRODUCTION 3-1
BLOCK DIAGRAM 3-1
CH 1AND CH 2ATTENUATORS 3-1
CH 1AND CH 2AMPLIFIERS 3-2
DISPLAY SWITCHING AND OUTPUT 3-3
CH 1AND CH 2READOUT 3-3

TABLE OF CONTENTS (cont)
SECTION 4MAINTENANCE Page
INTRODUCTION 4-1
PREVENTIVE MAINTENANCE 4-1
General 4-1
Cleaning 4-1
Lubrication 4-1
TROUBLESHOOTING 4-1
General 4-1
Troubleshooting Aids 4-1
Troubleshooting Equipment 4-1
Troubleshooting Procedure 4-2
CORRECTIVE MAINTENANCE 4-3
General 4-3
Obtaining Replacement Parts 4-3
Soldering Techniques 4-3
Component Replacement 4-4
Circuit Board Removal 4-4
Switch Replacement 4-5
Recalibration After Repair 4-6
SECTION 5CALIBRATION
PRELIMINARY INFORMATION 5-1
Calibration Interval 5-1
Tektronix Field Service 5-1
Using This Procedure 5-1
TEST EQUIPMENT REQUIRED 5-1
General 5-1
Special Calibration Fixtures 5-1
Calibration Equipment Alternatives 5-1
Preliminary Procedure 5-3
PART I-PERFORMANCE CHECK 5-4
Introduction 5-4
Outline for Part 1-Performance Check 5-4
Performance Check 5-4
PART II -SHORT-FORM PROCEDURE 5-7
Introduction 5-7
Short- Form Procedure 5-7
PART III -CALIBRATION PROCEDURE 5-10
Introduction 5-10
Outline for Part 3-Calibration Procedure 5-10
Calibration Procedure 5-10
SECTION 6ELECTRICAL PARTS LIST
Parts Ordering Information
Abbreviations
SECTION 7DIAGRAMS AND CIRCUIT BOARD ILLUSTRATIONS
Symbols and Reference Designators

7A24
TABLE OF CONTENTS (cont)
SECTION 8MECHANICAL PARTS LIST
Parts Ordering Information
Abbreviations
CHANGE INFORMATION
LIST OF ILLUSTRATIONS
Number Page
T1 7A24 Dual-Trace Amplifier.
1-2 Release Latch. 1-1
1-3 7A24 Front-Panel Controls and Connectors. 1-2
1-4 Measuring the peak-to-peak voltage of awaveform. 1-4
1-5 Measuring instantaneous voltage with respect to
some reference. 1-5
1-6 Measuring phase difference between two signals. 1-7
1-7 High resolution phase measurement using time-base magnifier. 1-7
1-8 Using the ADD mode for common-mode rejection. 1-8
5-1 Test circuit for Input Resistance Check/Adjust. 5-3
5-2 Location of pins 1and 13, U1550. 5-7
5-3 -(-Signal Output location. 5-8
7-1 Semiconductor Electrode Configurations.
7-2 Circuit Board Locations.
7-3 A1 and A2 Attenuator Board.
7-4 A5 Amplifier Board.
7-5 A5 Amplifier Board.
7-6 A5 Amplifier Board.
7-7 A2 and A4 Readout Board.
7-8 Adjustment Locations.
LIST OF TABLES
2-1 Electrical Specifications. 2-1
2-2 Environmental Specifications. 2-2
2-3 Physical Specifications. 2-2
5-1 Test Equipment. 5-2
5-2 Vertical Deflection Check. 5-5
5-3 Vertical Deflection Adjust. 5-11
iii

mi @PUSH
VAHiaBLE (CAL INI
VOLTS/DIV
5VRMS MAX
INTERNALLV
FUSED
TiiiCCIIiR
SOURCS SPLAY
>09E
CH 2POLARITY
raa @PUSH
VARIABLE (CAL INI
VOLTS/DIV
6VRMS MAX
INTERNAUY
FUSED
tektROMxc DUAL TRACE AMPLIFIER
7A24
7A24 FEATURES
The 7A24 is a(jual-channel, wiide-bancjwidth amplifier plug-in unit (designed for use with Tektronix 7000-series
Oscilloscopes. Each channel has an input impedance of 50 ohms and is internally fused. Internal attenuators and gain circuits
are switched to correspond to the settings of the VOLTS/DIV switches. Channel 2can be inverted and added to channel 1for
differential measurements.
Fig. 1*1. 7A24 Dual-Trace Amplifier.
7A24

Section 1—7A24
OPERATING INSTRUCTIONS
PRELIMINARY INFORMATION
Installation
The 7A24 is calibrated and ready for use as received. It
can be installed in any compartment of Tektronix
7000-series oscilloscopes, but is principally used in vertical
plug-in compartments. To install, align the upper and lower
rails of the 7A24 with the oscilloscope tracks and fully
insert it. The front is flush with the front of the
oscilloscope when the 7A24 is fully inserted, and the latch
at the bottom-left corner of the 7A24 will be in place
against the front panel. See Fig. 1-2.
To remove the 7A24, pull on the latch (which is
inscribed with the unit identification "7A24") and the
7A24 will unlatch. Continue pulling on the latch to slide
the 7A24 out of the oscilloscope.
RELEASE
LATCH
Fig. 1-2. Release Latch.
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 1or CH 2and connecting the signal to be observed to
the appropriate input. In the discussions to follow,
single-trace operations using CH 1only apply equally to
CH 2only.
Signal Connections
The 50-ohm input impedance of the 7A24 is ideally
suited for making waveform measurements on 50-ohm
systems, in that 50-ohm coaxial cables can be connected
directly to the input of the 7A24. The 7A24, however,
should not be connected directly to apower supply, power
line, or other voltage source that would exceed the input
voltage limits of the 7A24 (see Specification section. Table
2-1). Probes recommended for use with the 7A24 are the
P6056 (10X) and P6057 (100X). Both probes are com-
patible with 50-ohm systems, and will allow optimum
frequency response. These probes also contain trace
IDENTIFY and readout encoding functions, Aone-
megohm imput impedance may be achieved by using the
P6051 FET Probe.
Vertical Gain Check and Adjustment
To check the gain of either channel, set the VOLTS/D IV
switch to 5mV and connect a40-millivolt, one-kilohertz
signal (20-millivolts when terminated by 50-ohms) from the
oscilloscope calibrator to the input connector of the
channel 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 turning the knob with anarrow-blade screwdriver
(see Fig. 1-3, 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 1and Channel 2Input (OFF-DC) switches
select the signal input coupling mode.
DC. The DC position couples both ac and dc compo-
nents of the signal into the input amplifier. A50-ohm
impedance is presented to the signal source.
1-1

Operating Instructions—7A24
CH 1POSITION
Controls position of the CH 1trace
and ADD display mode trace.
CH 1input connector
provides signal connection to CH 1.
CH 2POLARITY
Provides means of inverting the CH
2display.
CH 2POSITION
Controls the position of the CH 2
trace only. Disabled in ADD.
IDENTIFY (same as CH 1)
Deflects trace about 0.2 division for
trace identification, in instruments
with readout also replaces readout
with the word IDENTIFY.
CH 2input connector
Provides signal connection to CH 2.
TRIGGER SOURCE
Selects source of the trigger signal.
DISPLAY MODE
Selects the mode of operation.
VARIABLE VOLTS/DIV (same as
CH 1)
Provides continuously variable
uncalibrated settings between caii*
brated steps.
GAIN adjustment
When the VARIABLE control is
pushed in, it becomes afront-panel
screwdriver adjustment for calibra-
tion of deflection factor.
VOLTS/DIV (same as CH 1)
Selects calibrated deflection factors
from 5mV/div to 1V/div; eight
steps in a1-2-5 sequence.
Input (same as CH 1
)
Selects signal input mode.
Fig. 1-3. 7A24 Front-Panel Controls and Connectors.

Operating Instructions—7A24
OFF. The OFF position disconnects the signal source
from the amplifier and connects it to aresistive 50-ohm
termination.
Input Protection Fuse
Afuse in the input of each channel protects the 7A24
from damage due to excessive signal voltages. If this fuse is
open, no display can be obtained. If no waveform can be
displayed, but the POSITION control will move the trace
on the crt, check the condition of the fuse.
The thick film, ceramic fuse is located on the front of
the Attenuator circuit board. Aspare fuse is stored on the
rear of the board. (See the Maintenance section of this
manual for fuse replacement instructions.) If fuse replace-
ment is necessary, order anew fuse to replace the spare.
VOLTS/DIV and VARIABLE Controls
The amount of vertical deflection produced by asignal is
determined by the signal amplitude, the attenuation factor
of the probe, the setting of the VOLTS/D IV switch, and
the setting of the VARIABLE control. Calibrated 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 counter-
clockwise and the VOLTS/DIV switch set to 1volt/division
the uncalibrated vertical deflection factor is extended to at
least 2.5 volts/division. By applying acalibrated voltage
source to the input connector, any specific deflection
factor can be set within the range of the VARIABLE
control.
CH 2POLARITY Switch
The CH 2POLARITY switch may be used to invert the
displayed waveform of the signal applied to the CH 2input.
This is particularly useful in added operation of the 7A24
when differential measurements are to be made. The CH 2
POLARITY switch has two positions, -HJP and INVERT. In
the -tUP position, the displayed waveform will have the
same polarity as the applied signal and apositive dc voltage
will move the crt trace up. In the INVERT position, a
waveform at the CH 2input will be displayed on the crt in
inverted form and apositive dc voltage will move the trace
down.
DISPLAY MODE Switch
For single-trace operation, apply the signal either to the
CH 1input or the CH 2input and set the DISPLAY MODE
switch to the corresponding position: CH 1or CH 2.
To display asignal 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 1or CH 2position.
Alternate Mode. The ALT position of the DISPLAY
MODE switch produces adisplay which alternates between
Channel 1and Channel 2with each sweep on the crt.
Although the ALT mode can be used at all sweep rates, the
CHOP mode provides amore satisfactory display at sweep
rates below about 0.5 millisecond/division. At slow sweep
rates, alternate mode switching becomes visually
perceptible.
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 adc voltage to one channel
to offset the dc component of asignal 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 1and CH 2VOLTS/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 adisplay which is electronically
switched between channels at approximately a500 kilo-
hertz rate (controlled by mainframe). In general the CHOP
mode provides the best display at sweep rates slower than
about 0.5 millisecond/division or whenever dual-trace,
non-repetitive phenomena is to be displayed.
TRIGGER SOURCE Switch
CH 1. The CH 1position of the TRIGGER SOURCE
switch provides a trigger signal obtained from the signal
applied to the CH 1input connector. This provides astable
display of the signal applied to the CH 1input connector.
CH 2. The CH 2position of the TRIGGER SOURCE
switch provides atrigger signal obtained from the signal
applied to the CH 2 input connector. This provides astable
display of the signal applied to the CH 2input connector.
MODE. In this position of the TRIGGER SOURCE
switch, the trigger signal for the time-base unit is dependent

Operating Instructions—7A24
on the setting of the DISPLAY MODE switch. The trigger
source for each position of the DISPLAY MODE switch is
as follows:
mode trigger signal source
CH 1Channel 1
CH 2Channel 2
ADD Algebraic sum of Channel 1and Channel 2
CHOP Algebraic sum of Channel 1and Channel 2
ALT Alternates between Channel 1and Channel 2
Trace Identification
When the IDENTIFY button is pressed, the trace is
deflected about 0.3 division to identify the 7A24 trace.
This feature is particularly useful when multiple traces are
displayed. In instruments with readout, pressing the
IDENTIFY button also replaces the deflection factor
readout with the word "IDENTIFY",
BASIC APPLICATIONS
General
The following information describes the procedures and
techniques for making basic measurements with a7A24 and
the associated Tektronix oscilloscope and time-base. These
applications are not described in detail since each applica-
tion must be adapted to the requirements of the individual
measurements. This instrument can also be used for many
applications not described in this manual. Contact your
local Tektronix Field Office or representative for assistance
in making specific measurements with this instrument.
Peak-to-Peak Voltage Measurements
To make peak-to-peak voltage measurements, use the
following procedure:
6.
Turn the 7A24 POSITION control so the lower
portion of the waveform coincides with one of the graticule
lines below the center horizontal line, and the top of the
waveform is within the viewing area. With the time-base
Position control, move the display so one of the upper
peaks lies near the center vertical line (see Fig. 1-4).
Fig. 1-4. Measuring the peak-to-peak voltage of awaveform.
7.
Measure the divisions of vertical deflection peak-to-
peak. Check that the VARIABLE (VOLTS/DIV) control is
in the CAL IN position.
NOTE
This technique can also be used to make measure-
ments between two points on the waveform, rather
than peak to peak.
8.
Multiply the deflection measured in step 7by the
VOLTS/DIV switch setting. Include the attenuation factor
of the probe if used.
1.Apply the signal to either input connector.
2. Set the DISPLAY MODE and TRIGGER SOURCE
switches to display the channel used.
3. Set the Input switch to DC.
EXAMPLE: Assume that the peak-to-peak vertical
deflection is 4.5 divisions (see Fig. 1-4) using a10X
attenuator probe, and the VOLTS/DIV switch is set to 1V.
Volts
Peak to Peak
vertical
=deflection
(divisions)
XVOLTS/DIV
setting
probe
Xattenuation
factor
4. Set the VOLTS/DIV switch to display about five Substituting the given values:
divisions of the waveform vertically.
Volts Peak-to-Peak =4.5 X1X10
5. Set the time-base Triggering controls for astable
display. Set the time-base unit to asweep rate that displays
several cycles of the waveform. The peak-to-peak voltage is 45 volts.
1-4

Operating Instructions—7A24
Instantaneous Voltage Measurements
To measure the dc level at agiven point on awaveform,
proceed as follows;
1
,
Connect the signal to either input connector.
2.
Set the DISPLAY MODE and TRIGGER SOURCE
switches to display the channel used.
3.
Set the VOLTS/DIV switch to display about five
divisions of the waveform.
4.
Set the Input switch to OFF and position the trace to
the bottom graticule line or other reference line. If the
voltage is negative with respect to ground, position the
trace to the top graticule line. Do not move the POSITION
control after this reference line has been established.
NOTE
To measure avoltage level with respect to avoltage
other than ground, make the following changes to
step 4. Set the Input switch to DC and apply the
reference voltage to the input connector. Then
position the trace to the reference line.
Fig. 1-5. Measuring instantaneous voltage with respect to some
reference.
EXAMPLE; Assume the vertical distance measured is 3.6
divisions (see Fig. 1-5) and the waveform is above the
reference line using a10X probe with aVOLTS/DIV setting
of ,5 V.
Using the formula;
Instan- vertical VOLTS/ probe
taneous =distance Xpolarity XDIV Xattenuation
Voltage (divisions) setting factor
5. Set the Input switch to DC. The ground reference line
can be checked at any time by switching to the OFF
position.
Substituting the given values:
Instantaneous
Voltage =3,6 X+1 X0.5 V X 10
6.
Set the time-base Triggering controls for astable
display. Set the time-base sweep rate for an optimum The instantaneous voltage is 18 volts,
display of the waveform.
7.
Measure the distance in divisions between the refer-
ence line and the point on the waveform at which the dc
level is to be measured. For example, in Fig. 1-5 the
measurement is between the reference line and point A.
8.
Establish the polarity of the waveform. With the CH 2
POLARITY switch in the +UP position, any point above
the reference line is positive.
9.
Multiply the distance measured in step 7by the
VOLTS/DIV setting. Include the attenuation factor of the
probe, if used.
Comparison Measurements
In some applications it may be desirable to establish
arbitrary units of measurement other than those indicated
by the VOLTS/DIV switch. This is particularly useful when
comparing unknown signals to areference amplitude. One
use for the comparison-measurement technique is to
facilitate calibration of equipment where the desired
amplitude does not produce an exact number of divisions
of deflection. The adjustment will be easier and more
accurate if arbitrary units of measurement are established
so that the correct adjustment is indicated by an exact
number of divisions of deflection. The following procedure
describes how to establish arbitrary units of measure for
comparison measurements.
1-5

Operating Instructions—7A24
To establish an arbitrary vertical deflection factor based
upon aspecific reference amplitude, proceed as follows:
Vertical
Conversion =
Factor
3V
4X,5 V1.5
1.
Connect the reference signal to the input connector.
Set the time-base unit sweep rate to display several cycles
of the signal.
2. Set the VOLTS/DIV switch and the VARIABLE
control to produce adisplay which is an exact number of
vertical divisions in amplitude. Do not change the VARI-
ABLE control after obtaining the desired deflection.
Then with aVOLTS/DIV setting of .2 V, the peak-to-
peak amplitude of an unknown signal which produces a
vertical deflection of five divisions can be determined by
using the signal amplitude formula (step 6):
Signal
Amplitude .2 V X 1.5 X5=1.5 volts
3.
To establish an arbitrary vertical deflection factor so
the amplitude of an unknown signal can be measured
accurately at any setting of the VOLTS/DIV switch, the
amplitude of the reference signal must be known. If it is
not known, it can be measured before the VARIABLE
VOLTS/DIV control is set in step 2.
4.
Divide the amplitude of the reference signal (volts) by
the product of the vertical deflection (divisions) established
in step 2and the setting of the VOLTS/DIV switch. This is
the vertical conversion factor.
reference signal
Vertical amplitude (volts)
Conversion =vertical VOLTS/DIV
Factor deflection Xswitch
(divisions) setting
5.
To measure the amplitude of an unknown signal,
disconnect the reference signal and connect the unknown
signal to the input connector. Set the VOLTS/DIV switch
to asetting that provides sufficient vertical deflection to
make an accurate measurement. Do not re-adjust the
VARIABLE control.
Dual-Trace Phase Difference Measurements
Phase comparison between two signals of the same
frequency can be made using the dual-trace feature of the
7A24. This method of phase-difference measurement can
be used up to the frequency limit of the oscilloscope
system. To make the comparison, use the following
procedure:
1.Set the CH 1and CFI 2Input switches to DC.
2. Set the DISPLAY MODE to ALT or CHOP. In
general, CHOP is more suitable for low frequencies and
ALT is more suitable for high frequencies. Set the
TRIGGER SOURCE to CH 1.
3.
Connect the reference signal to the CH 1input and
the comparison signal to the CH 2input. Use coaxial cables
or probes which have similar time-delay characteristics to
connect the signals to the input connectors.
4.
If the signals are of opposite polarity, set the CH 2
POLARITY switch to invert the Channel 2display. (Signals
may be of opposite polarity due to 180° phase difference;
if so, take this into account in the final calculation.)
6.
Measure the vertical deflection in divisions and
calculate the amplitude of the unknown signal using the
following formula.
5.
Set the VOLTS/DIV switches and the VARIABLE
controls of the two channels so the displays are equal and
about five divisions in amplitude.
Signal ^VOLTS/DIV
Amplitude setting
vertical vertical
Xconversion Xdeflection
factor (divisions)
6. Set the time-base unit to asweep rate which displays
about one cycle of the waveforms. Set the Triggering
controls for astable display.
EXAMPLE: Assume areference signal amplitude of 3
volts, aVOLTS/DIV setting of ,5 Vand the VARIABLE
control adjusted to provide avertical deflection of four
divisions. Substituting these values in the vertical conver-
sion factor formula (step 4):
7.
Center the waveforms on the graticule with the
7A24 POSITION controls.
8.
Adjust the time-base Variable Time/Div control until
one cycle of the reference signal occupies exactly eight
1-6

Operating Instructions—7A24
horizontal divisions between the second and tenth vertical
lines of the graticule (see Fig. 1-6). Each division of the
graticule represents 45° of the cycle (360° ^8divisions =
45°/division). The sweep rate can now be stated in terms of
degrees as 45°/division.
9. Measure the horizontal difference between corre-
sponding points on the waveform.
High Resolution Phase Measurements
More accurate dual-trace phase measurements can be
made by increasing the sweep rate (without changing the
Variable Time/Div control). One of the easiest ways to
increase the sweep rate is with the time-base Magnifier
switch. Set the Magnifier to X10 and determine the
magnified sweep rate by dividing the sweep rate obtained
previously by the amount of sweep magnification.
10. Multiply the measured distance (in divisions) by
45°/division to obtain the exact amount of phase
difference.
EXAMPLE: Assume ahorizontal difference of 0.3
division with asweep rate of 45°/division as shown in
Fig. 1-6.
Using the formula:
EXAMPLE: If the sweep rate is increased 10 times by
the Magnifier, the magnified sweep rate is 45°/division Tio
=4.5 /division. Fig. 1-7 shows the same signals as used in
Fig. 1-6 but with the Magnifier set to X10. With a
horizontal difference of 3divisions, the phase difference is:
horizontal magnified
Phase Difference =difference Xsweep rate
(divisions) (degrees/division)
Phase Difference
horizontal
difference X
(divisions)
sweep rate
(degrees/division)
Substituting the given values:
Phase Difference =0.3 X45°
The phase difference is 13,5°.
Fig. 1-6. Measuring phase difference between two signals.
Substituting the given values:
Phase Difference =3X4.5°
The phase difference is 13.5°.
Fig. 1-7. High resolution phase measurement using time-base
magnifier.
Common Mode Rejection
The ADD feature of the 7A24 can be used to display
signals which contain undesirable components. These
1-7

Operating Instructions—7A24
undesirable components can be eliminated through
common-mode rejection. The procedure is as follows:
1
.
Set the DISPLAY MODE switch to ALT or CHOP and
the TRIGGER SOURCE switch to MODE,
2.
Connect the signal containing both the desired and
undesired information to the CH 1input connector.
3.
Connect asignal similar to the unwanted portion of
the CH 1signal to the CH 2 input connector. For example,
in Fig. 1-8 aline-frequency signal is connected to channel 2
to cancel out the line-frequency component of the channel
1signal.
4.
Set both Input switches to the DC position.
5.
Set the VOLTS/D IV switches so the signals are about
equal in amplitude.
6.
Set the DISPLAY MODE switch to ADD. Set the
CH 2POLARITY switch to INVERT so the common-mode
signals are of opposite polarity.
7.
Adjust the Channel 2VOLTS/D IV switch and
VARIABLE control for maximum cancellation of the
common-mode signal. The signal which remains should be
only the desired portion of the channel 1signal.
EXAMPLE: An example of this mode of operation is
shown in Fig. 1-8. The signal applied to Channel 1contains
unwanted line-frequency components (Fig. 1-8A). Acorre-
sponding line-frequency signal is connected to Channel 2
(Fig. 1-8B). Fig. 1-8C shows the desired portion of the
signal as displayed when common-mode rejection is used.
(A) CHANNEL 1SIGNAL.
-m•1m^^'«•m
(C) RESULTANT DISPLAY.
The above procedure can also be used for examining a
signal superimposed on some dc level. Adc voltage of the
proper polarity applied to Channel 2 can be used to cancel
out the dc portion of the signal applied to Channel 1.
Fig. 1-8. Using the ADD mode for common-mode rejection. (A)
Channel 1signal contains desired information along with line-
frequency component. (B) Channel 2 contains line frequency only.
(C) Resultant CRT display using common-mode rejection.

Section 2—7A24
SPECIFICATION
Introduction
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 atwenty-minute warmup unless otherwise noted.
TABLE 2-1
Electrical
Characteristic Performance Requirement Supplemental Information
Deflection Factor
Calibrated Range 5mV/Div to 1V/Div; eight steps in a1,
2, 5sequence.
Gain Ratio Accuracy Within 2% of indicated deflection factor
with GAIN adjusted at 5mV/Div.
Uncalibrated (VARIABLE) Continuously variable between calibrated
steps; extends deflection factor to at least
2.5 volts per division.
GAIN Range Permits adjustment of deflection factor
for calibrated operation with all 7000
-series oscilloscopes.
Frequency Response Bandwidth Depends upon oscilloscope used. See the oscilloscope mainframe specifica-
tions or the current Tektronix catalog.
Maximum Input Voltage 5volts (0.5 watts). Up to 10 volts (2 watts) can be applied to
the input without damage to the instru-
ment.
Input Characteristics
DC Resistance
VSWR
50.0 ohms, within 2%.
Equal to, or less than 1.25 at 5mV and
10 mV; equal to, or less than 1.15 at
20 mV to 1V; from dc to 350 MHz.
Overdrive Recovery Time 0.1 millisecond or less to recover to
within one division after removal of
over-drive signal of up to +lb divisions or
—75 divisions regardless of overdrive
signal duration.
2-1

Specification—7A24
Characteristic Performance Requirement Supplemental Information
Delay Time Difference
Between Channels 200 picoseconds or less.
Channel Isolation 50:1 display ratio up to 200 megahertz.
Common Mode Rejection Ratio At least 10: 1,dc to 50 MHz.
Chop Frequency See the oscilloscope mainframe specifi-
cations.
Display Modes Channel 1only.
Dual-trace, alternate between channels.
Added algebraically.
Dual-trace, chopped between channels.
Channel 2only.
Trigger Source Selection Channel 1only.
Follows DISPLAY MODE selection.
Channel 2only.
TABLE 2-2
Environmental
Refer to the specification for the associated mainframe.
TABLE 2-3
Physical
Size Fits all 7000-series plug-in compartments.
Weight 2Pounds 9Ounces (1.2 Kilograms).
2-2

Section 3—7A24
THEORY OF OPERATION
INTRODUCTION
This section of the manual contains adescription of the
circuitry used in the 7A24. The 7A24 description begins
with adiscussion of the instrument using the block diagram
shown in the Diagrams section. Then, each circuit is
described in detail using the block diagram to show the
interconnections between stages in each major circuit and
the relationship of the front-panel controls to the individual
stages.
Complete schematics of each circuit are given in the
Diagrams section. Refer to these schematics throughout the
following circuit description for electrical values and
relationship.
BLOCK DIAGRAM
The Channel 1Amplifier circuit provides gain setting,
variable gain control, and trace positioning. The Channel 2
Amplifier provides signal-polarity inversion in addition to
gain setting, variable gain control, and trace positioning.
The signal to be displayed on the crt is applied to the
CH 1or CH 2input connector. The signal passes through
the Input switch, where it is either connected to the
attenuators or to a50-ohm dummy load. The VOLTS/DIV
switch selects the correct amount of attenuation, and the
signal is passed to the Switched-Gain Amplifier.
When the VOLTS/DIV switch is set to the 5mV and
10 mV positions, the signal connected to the input
connector is passed through the attenuators without
attenuation. When the VOLTS/DIV switch is set in the
5mV position, the Switched-Gain Amplifier operates at full
gain. In all other positions of the VOLTS/DIV switch, the
gain of the Switched-Gain Amplifier is reduced by two.
Internal gain and balance adjustments are included in the
Switched-Gain Amplifier.
Overall GAIN and VARIABLE gain are adjusted in the
Gain Amplifier. Variable Balance and high-frequency
adjustments are also controlled in the Gain Amplifier. The
output of the Gain Amplifier is connected to the
Positioning circuitry where the POSITION and IDENTIFY
functions are controlled. Channel 2is identical to Channel
1, with the exception of the polarity-inversion function in
Channel 2.
The Display and Trigger Channel Switching Amplifiers
provide differential signal outputs for the signal and trigger
lines, from each channel, to acommon display and trigger
output.
The output of the Display and Trigger Channel
Switching Amplifiers are connected to the oscilloscope
mainframe via the interface connector.
Readout encoding circuitry used in the 7A24 is standard
to the 7000-series.
CH 1AND CH 2ATTENUATORS
NOTE
The CH 1and CH 2amplifier circuits are identical
with the exception of the CH 2GAIN stage U2450,
which includes aPOLARITY inverting circuit. Oniy
CH 1is described in detail throughout this discussion.
Delay Line and Fuse
Signals connected to the input connector passthrough a
delay line and a0.2 amp. fuse (F100) before reaching the
Input switch. The delay line is used to produce a
standardized time delay through the plug-in. The fuse
protects the attenuators and amplifier by preventing
excessive voltages from reaching these components.
Input Switch
Input signals can be dc-coupled or internally discon-
nected. S100A is acam-type switch; acontact-closure chart
showing the operation is given on the schematic diagrams.
When the Input switch is in the DC position, the input
signal is connected to the attenuators. The OFF position
opens the signal path to the attenuators and connects the
input to an internal 50-ohm dummy load. This provides a
ground reference without the need to disconnect the
applied signal from the input connector, while presenting a
constant 50-ohm load at the input connector.
Input Attenuator
The effective overall deflection factor of the 7A24 is
determined by the setting of the VOLTS/DIV switch,
S100B. The basic deflection factor is 5millivolts per
division of crt deflection. To increase the deflection factor
3-1

Theory of Operation—7A24
to the values indicated on the front panel, precision
attenuators are switched into the circuit. S100B is a
cam-type switch. The dots on the contact-closure chart (see
Diagram 1)indicate when the associated contacts are in the
position shown (open or closed). In the 5mV/Div and
lOmV/Div positions, the attenuators are not used; the
input signal is connected directly to the Switched-Gain
Amplifier. The lOmV/Div position decreases the gain of
the Switched-Gain Amplifier. For switch positions above
lOmV/Div, the attenuators are switched into the circuit,
singly or stacked, to produce the deflection factor indicated
on the front panel. The hybrid attenuators are constant
impedance, T-pad dividers. In addition to providing
constant attenuation at all frequencies within the band-
width of the instrument, the input attenuators are designed
to maintain the same input impedance (50 ohms) for all
settings of the VOLTS/D IVswitch.
CH 1AND CH 2AMPLIFIERS
Switched-Gain Amplifier
The coax coupler between the Attenuator circuit board
and the Main Amplifier circuit board acts as abalun
transformer to provide differential drive to U1350 at high
frequencies. U1350 is aparaphase-type amplifier with dual
differential outputs.
In the 5mV position, full drive is provided from pins 5
and 9of U1350 to the U1450 load resistors, R1401 and
R1403. In all other attenuator positions, the signal-path
drive current through the load resistors is divided in half.
The other half is diverted through pins 6and 8of U1350
and is dissipated in dummy-load resistors R1341 and
R1343. R1337 sets the basic gain of amplifier U1350.
R1317 is used to divide the basic gain by afactor of two
for ail positions of the VOLTS/DIV switch except 5mV.
CR1319 and R1319 maintain proper collector voltage
while switching between the 5mV and 10 mV positions.
Cl 332 and R1332 are thermal compensations. R1336 and
Cl 336 are high-frequency adjustments.
Fixed length inductors and capacitors are part of the
Amplifier etched circuit board and provide T-coil peaking
at the input of U1350.
Gain Amplifier
U1450 is avariable-gain cascode amplifier which sets the
overall channel gain. The GAIN (R1423A) and VARIABLE
(R1423B) controls determine the ratio of base currents
through pins 11 and 12 of U1450. The base-current ratio
determines the shared collector output levels between pins
5, 6and 8, 9.
R1436 provides adjustable low-frequency compensation.
R1434, C1436, and RT1437 compensate for temperature
variations. R1435, C1435, R1445, and L1445 are adjust-
able high-frequency compensations. U1450 input T-coil
peaking inductors and capacitors are part of the etched
circuit board. Dc balance over the variable range is adjusted
by R1353.
Position Circuit
Positioning current is added to the signal current of
111450 output from current sources Q1470 and Q1490.
R1465 controls the voltage at the bases of the current
sources, which in turn determines the amount of position-
ing current added. R1467, R1465, and CR1465 provide
trace shift current for the IDENTIFY function.
Display Channel Switching Amplifier
The third cascode amplifier, U1550, is used for
controlling the Channel 1display modes. When the
DISPLAY CH 1ON level at pin 11 is HI, the Channel 1
signal passes through the transistor pair with outputs at pins
6and 8to the level shifters. At the same time the
DISPLAY CH 1OFF level at pin 12 is LO, turning off the
second transistor pair collectors, pins 5and 9. When pin 11
is Hi, Channel 1is displayed and when pin 12 is HI Channel
1is not displayed. Pins 11 and 12 are always in opposite
states, the levels being selected by the DISPLAY MODE
switch S30A.
Trigger Channel Switching Amplifier
U1750 is acascode amplifier used as the trigger switch,
and operates similarly to the Display Channel Switching
Amplifier, U1550. The' TRIGGER SOURCE switch, S30B
determines the base levels on pins 11 and 12 of U1750 for
trigger selection.
Output Level Shifting
Zener diodes, VR850, VR854, VR860, and VR864 are
used to return the display signal dc level to zero volts at the
plug-in interface. C850 and C860 provide ahigh-frequency
path around the zener diodes. R894 balances the differen-
tial output, and R896 sets the common-mode level to zero
volts. These adjustments compensate for variations in the
zener diodes.
Trigger Output Amplifier
Common base transistors Q920 and Q940 are used as
Trigger Output dc level shifters to return the dc level to
zero volts at the plug-in interface.
3-2

Theory of Operation—7A24
Channel 2Gain-Polarity Amplifier
CH 2operation is the same as CH 1. For circuit number
reference the prefix number for CH 1is 1and CH 2is 2.
For instance, U2350 functions in CH 2the same as does
U1350 in CH 1, In CH 2aPolarity feature is included in
the second cascode amplifier, U2450. S22A allows base
drives to be reversed to U2450. Polarity Gain R2411,
matches the gain in both polarity positions.
DISPLAY SWITCHING AND OUTPUT
Translator
The Translator, Q1050 and Q1070, increase the CHOP
and ALT control logic levels from the mainframe to a
usable level in the 7A24. CR1060 and CR1062 keep Q1050
and Q1070 from going into saturation.
CH 1AND CH 2READOUT
Readout Encoding
The Readout Encoding circuit consists of switching
resistors and probe sensing stage Q620. This circuit encodes
the Channel 1and 2, Row and Column output lines for
readout of deflection factor, uncalibrated deflection factor
(VARIABLE) information, and signal inversion (Channel 2
only). Data is encoded on these output lines by switching
resistors between them and the time-slot input lines, or by
adding current through Q620.
R647-CR647 are switched between time-slot three
(TS-3) and Column output line when the CAL IN switch is
in the uncal position. This results in the symbol >(greater
than) being displayed preceding the deflection factor
readout. R648 (Channel 2only) is switched between TS-2
and the Column output line when the CH 2POLARITY
switch is in the INVERT position. This results in the
symbol 4- (inverted) being displayed preceding the deflec-
tion factor readout.
Switching resistors are used to indicate the setting of the
VOLTS/DIV switch to the mainframe readout system. The
VOLTS/DIV switch is acam-type switch. The dots on the
contact-closure chart (see Diagram 5) indicate when the
associated contacts are closed. R633, R634, and R635
select the number 1, 2, or 5depending on the resistor
combination that is switched in. R637 selects the m(milli-)
prefix and R639 selects the symbol V(volts) in the 5mV
through .5 V(500 mV) positions of the VOLTS/DIV
switch. R638 selects the symbol Vin the 1Vposition.
R630, R631, and the output of the probe sensing stage
(Q620) select the decimal point (number of zeroes) again
depending on the resistor combination switched in by the
VOLTS/DIV switch.
Probe sensing stage 0620 identifies the attenuation
factor of the probe connected to the input connector by
sensing the amount of current flowing from the current
sink through the probe coding resistance. The output of
this circuit corrects the mainframe readout system to
include the probe attenuation factor. The third contact of
the input connector provides the input to the probe sensing
stage from the probe coding resistance (coded probes only;
see Operating Instructions). The third contact is also used
for the IDENTIFY input. The coding resistor forms a
voltage divider with R621 through CR621 to the —15 V
supply. The resultant voltage sets the bias on Q620 and
determines, along with emitter resistor R622, the collector
current. When the —15 volt time-slot pulse is applied to
Interface Connector B33, Q620 is interrogated and its
collector current is added to the Column current output
through Interface Connector A37.
With aIX probe (or no probe) connected to the input
connector, Q620 is turned off. The deflection factor
readout is determined by the VOLTS/DIV switch position.
With a10X probe connected, the bias on Q620 will allow
100 microamperes of collector current to flow. This
increases the deflection factor readout by afactor of 10.
The IDENTIFY button (S1465 on Diagram 2or S2465
on Diagram 3) does two things when pressed:
1. It causes the trace representing the appropriate
channel of the 7A24 to move about 0.3 division (see the
Front-Panel Controls and Connectors, Fig. 1-3).
2. It forward biases CR621 and Q620 to result in a
sufficient amount of collector current which, when added
to the Column current output, replaces the deflection
factor readout with the word "IDENTIFY”.
These two actions aid in identifying the 7A24 trace
when multiple traces are displayed. When the IDENTIFY
button is released, the deflection factor readout and trace
position are restored.
CR1465 in CH 1, and CR2465 in CH 2isolate readout
circuitry from the position circuitry. For further informa-
tion on the operation of the readout system, see the
oscilloscope instruction manual.
3-3