Tektronix 7a15a User manual

INSTRUCTION
IVIAIM UAL
7A1SA/AN
AMPLIFIER
Tektronix, Inc ®P. O. Bo* 500 •Beoverton, Oregon 97005 •Phone [phone] •Cables:
070-1210-00
Tektronix
871

WARRANTY
All Tektronix instruments are warranted against
defective materials and workmanship for one year.
Any questions with respect to the warranty,
mentioned above, should be taken up with your
Tektronix Field Engineer or representative.
All requests for repairs and replacement parts
should be directed to the Tektronix Field Office or
representative in your area. This procedure will assure
you the fastest possible service. Please include the
instrument Type (or Part Number) and Serial or
Model Number with all requests for parts or service.
Specifications and price change privileges reserved.
Copyright ©1971 by Tektronix, Inc., Beaverton,
Oregon. Printed in the United States of America. All
rights reserved. Contents of this publication may not
be reproduced in any form without permission of the
copyright owner.
U.S.A. and foreign Tektronix products covered
by U.S. and foreign patents and/or patents pending.

7A15A/7A15AN
TABLE OF CONTENTS
SECTION 1SPECIFICATION Page SECTION 5CALIBRATION Page
Introduction 1-1 Introduction 51
Electrical Characteristics 1-1 Test Equipment Required 5-1
Environmental Characteristics 1-2 Performance Check Procedure 5-2
Physical Characteristics 1-2 Calibration Procedure 52
SECTION 2OPERATING INSTRUCTIONS
SECTION 6ELECTRICAL PARTS LIST
Installation 2-1
Controls and Connectors 2-1 Abbreviations and Symbols
Basic Operation 2-2 Parts Ordering Information
General Operating Information 2-2
Applications 23
SECTION 7DIAGRAMS AND CIRCUIT BOARD
SECTION 3CIRCUIT DESCRIPTION ILLUSTRATIONS
Introduction 3-1 Symbols and Reference Designators
Block Diagram Description 31
Detailed Circuit Description 31
SECTION 8MECHANICAL PARTS LIST
SECTION 4MAINTENANCE Mechanical Parts List Information
Preventive Maintenance 4-1 Index of Mechanical Parts
Troubleshooting 4-1 Illustrations
Corrective Maintenance 4-3 Mechanical Parts List
REV. B. OCT. 1974 I

SECTION 1
SPECIFICATION
7A15A/7A15AN
Introduction
The 7A15A/7A15AN Amplifier plug-in unit is awide
band amplifier designed for use with Tektronix 7000-Series
oscilloscopes. The 7A15A and 7A15AN are electrically
identical except that encoding capabilities and an
"IDENTIFY" function are provided in the 7A15A. The
7A15A/7A15AN can be operated in any plug-in compart-
ment of 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 afive
minute warmup unless otherwise noted.
TABLE 1-1
ELECTRICAL
Characteristic Performance Requirement Supplemental Information
Deflection Factor
Calibrated Range 5mV/Div to 10 V/Div, 1 1 steps in a1-2-5
sequence
Deflection Factor Accuracy Within 2% of indicated deflection factor
with GAIN adjusted at 10 mV/Div
Uncalibrated (VARIABLE) Continuously variable between calibrated
steps; extends deflection factor to at least
25 V/Div
X10 GAIN Increases amplifier gain by afactor of 10
within 10%, decreasing deflection factor
to 500 pV/Div
Frequency Response
Upper Bandwidth Frequency
(at -3 dB)
XI (System Dependent)
i
With 7900-series
80 MHz
With 7700 series
75 MHz
With 7500-series
60 MHz
With 7400-series
50 MHz
X10 10 MHz
Low-Frequency Response 10 Hz or less without probe
(Lower —3 dB point)
AC (Capacitive) coupled
1Hz or less with probe

Specification -7A15A/7A15AN
TABLE 1-1 (cont)
Characteristic Performance Requirement
'
Supplemental Information
Maximum Input Voltage
DC Coupled 250 V(DC +Peak AC); AC component
500 VP-P maximum, 1kHz or less
AC Coupled 500 V(DC +Peak AC); AC component
500 VP-P maximum, 1kHz or less
Input Rand C
Resistance 1Mfi t2%
Capacitance Approximately 20.0 pf
RC Tolerance Within t1% between all deflection
factors.
Overdrive Recovery Time 0.1 ms or less to recover to within one
division after removal of overdrive signal
of up to +75 divisions to —75 divisions
regardless of overdrive signal duration
TABLE 1-2
ENVIRONMENTAL CHARACTERISTICS
Refer to the specifications for the associated oscilloscope
TABLE 1-3
PHYSICAL
Size Fits all 7000-series plug-in compartments
Weight 1pound 13 ounces (0.82 kilogram)

7A15A/7A15AN
SECTION 2
OPERATING INSTRUCTIONS
General
To effectively use the 7A15A/7A15AN, the operation
and capabilities of the instrument must be known. This
section describes front-panel control functions, general
information on signal input connections, and other subjects
that pertain to various measurement applications.
Installation
The 7A15A/7A15AN is calibrated and ready for use as
received. It can be installed in any compartment of Tek-
tronix 7000-Series Oscilloscopes, but is intended for use
primarily in vertical plug-in compartments. To install, align
the upper and lower rails of the 7A15A/7A15AN with the
oscilloscope tracks and insert the plug-in. The front panel
will be flush with the front of the oscilloscope when the
7A15A/7A15AN is fully inserted, and the latch at the
bottom-left corner will be in place against the front panel.
To remove the 7A15A/7A15AN, pull on the latch
(which is inscribed with the unit identification '7A15A" or
"7A15AN") and the 7A15A/7A15AN will unlatch.
Continue pulling on the latch to slide the 7A15A/7A15AN
out of the oscilloscope.
FRONT PANEL CONTROLS
AND CONNECTORS
VOLTS/DIV Selects calibrated deflection factors
from 5mV/Div to 10 V/Div; 11
steps in a1-2-5 sequence.
VARIABLE Provides continuously variable un-
calibrated settings between
calibrated steps. Extends the deflec-
tion factor range to 25 volts/
division or more.
GAIN Adjustment Screwdriver adjustment permits
calibration of deflection factor.
INVERT: Apositive-going signal at
the Input connector deflects the
CRT display downward.
MAG Provides means of decreasing the
deflection factor.
XI: Deflection factor is that
selected by VOLTS/DIV and
VARIABLE controls.
X10 REDUCED BANDWIDTH:
Deflection factor is one-tenth of
the value selected by the VOLTS/
DIV and VARIABLE controls.
Input Connector Provides signal connection to the
amplifier.
AC-GND-DC Selects signal input coupling mode.
AC: The AC component of the
signal is coupled to the amplifier
input, while the DC component is
blocked.
DC: Both AC and DC components
of the signal are coupled to the
amplifier input.
GND: Grounds the amplifier input
while maintaining the same load for
the input signal. Provides acharge
path for the AC coupling capacitor
to pre-charge the input circuit
before switching the input to AC.
nn, AniTw o-j .... .. POSITION Controls position of the trace.
POLARITY Provides means of inverting the
display. IDENTIFY Deflects trace about 0.3 division for
(7A15A Only) trace identification. In instruments
with readout, also replaces readout
with the word "IDENTIFY".
+UP: Apositive^oing signal at the
Input connector deflects the CRT
display upward.
2-1

Operating Instructions—7A15A/7A15AN
BASIC OPERATION
General. This procedure demonstrates the use of the
connectors and controls of the 7A15A/7A15AN, while at
the same time providing ameans of checking the basic
operation of the instrument.
Preliminary Setup. Install the 7A15A/7A15AN into any
7000-series oscilloscope vertical compartment and set the
oscilloscope VERTICAL MODE and TRIGGER SOURCE
to the proper settings.
Install a7-series time-base unit into ahorizontal
compartment and set the oscilloscope HORIZONTAL
MODE to the proper setting. Set the time base unit to a
sweep rate of one millisecond per division and set the
triggering mode to AUTO.
Procedure
1. Set the 7A15A/7A15AN AC-GND-DC switch to
GND and position the trace to the center of the graticule.
2. Set the VOLTS/DIV switch to 10 mV and apply a40
mV 1kHz square-wave signal from the oscilloscope CALI-
BRATOR to the 7A15A/7A1 5AN INPUT connector. Set
the AC-GND-DC switch to DC and check for afour division
display.
3. Set POLARITY switch to INVERT and check that
the displayed signal is inverted as compared to its appear-
ance in step 2.
4. Set the AC-GND-DC switch to AC and check that the
trace is centered on the CRT graticule.
5. Set the oscilloscope CALIBRATOR to 4mV and the
7A15A/7A15AN MAG switch to X10. Check for afour-
division display.
6. (7A15A Only) Press the 7A15A IDENTIFY button,
check that the display moves upward approximately 0.3
division and the readout (if so equipped) reads
"IDENTIFY".
GENERAL OPERATING INFORMATION
Signal Connections
In general, probes offer the most convenient means of
connecting asignal to the input of the 7A15A/7A15AN. A
10X attenuator probe offers ahigh impedance and allows
the circuit under test to perform very close to normal
operating conditions.
The Tektronix P6053 probe is equipped with areadout
coding ring which connects to acircuit in the amplifier
unit. This automatically corrects the readout displayed on
the CRT to the actual deflection factor at the tip of the
probe. This probe is recommended for use with the 7A15A
and an oscilloscope equipped with readout. The Tektronix
P6054 probe is electrically identical to the P6053 but is
intended for use with systems not equipped with readout.
For more information refer to the Tektronix Inc. catalog.
Vertical Gain Check and Adjustment
To check the gain of the 7A15A/7A15AN, set the
VOLTS/DIV switch to 10 mV and connect a40 mV. 1kHz
signal from the oscilloscope calibrator to the Input connec-
tor. The vertical deflection should be exactly four divisions.
If not. adjust the front panel GAIN for exactly four divi-
sions.
Input Coupling
The AC-GND DC switch allows achoice of input coup
ling methods. The type of display desired and the applied
signal will determine the coupling to use.
The DC coupling position can be used for most applica-
tions. For AC signals with frequencies below about 30 Hz
(10 Hz with a10X probe), and square waves whose low-
frequency components are important to the display, it is
necessary to use DC coupling to obtain asatisfactory
presentation.
In the AC coupling position the DC component of the
signal is blocked by acapacitor in the input circuit. The AC
coupling position provides the best display of signals with a
DC component much larger than the AC component. The
pre-charge feature should be used when there is apossibility
of having aresidual charge on the input capacitor of the
opposite polarity to the intended input, and when the
algebraic sum of the combination of charges may be greater
than the maximum input limitations of the amplifier. To
use this feature, first set the coupling switch to GND, then
connect the probe to the circuit and wait about two
seconds for the coupling capacitor to charge, set the
coupling switch to AC.
The GND position provides aground reference at the
input of the amplifier without externally grounding the
Input connectors. However, the signal connected to the
input is not grounded, and the same DC load is presented
to the signal source.
22 REV. B. OCT. 1974

Operating Instructions—7A15A/7 A15AN
VOLTS/DIV, VARIABLE and MAG Controls
The amount of deflection produced by asignal is deter-
mined by the signal amplitude, the attenuation factor of
the probe, the setting of the VOLTS/DIV switch, the
setting of the VARIABLE Control, and the setting of the
MAG switch. Calibrated deflection factors represented by
the setting of the VOLTS/DIV switch apply only when the
VARIABLE control is in the CAL position (fully clock-
wise) and when the MAG switch is set to XI.
The VARIABLE control provides variable uncalibrated
settings between the calibrated steps of the VOLTS/DIV
switch. With the VARIABLE control set fully counter-
clockwise and the VOLTS/DIV switch set to 5volts/div,
the uncalibrated deflection factor is extended to at least 2.5
times the attenuator setting. By applying acalibrated
voltage source to the Input connector, any specific deflec-
tion factor can be set within the range of the VARIABLE
control.
The MAG switch increases the VOLTS/DIV switch
sensitivity by afactor of 10 when in the X10 position.
Thus, with the MAG switch set to X10 and the VOLTS/
DIV switch set to 5mV/div, the deflection factor is
extended to 500 pV/div. The MAG switch also effects a
circuit in the 7A15A which corrects the readout. With the
MAG switch set to X10, the bandwidth of the amplifier is
reduced. Refer to specifications in Section 1.
Polarity Switch
The POLARITY switch provides ameans of inverting
the displayed signal. With the POLARITY set to +UP, a
positive-going signal at the INPUT produces an upward
deflection of the CRT display. With the POLARITY set to
INVERT, a positive-going signal will produce adownward
deflection of the CRT display.
Trace Identification (7A15A only)
When the IDENTIFY button is pressed, the trace is
deflected upward about 0.3 division to identify the 7A15A
trace. This feature is particularly useful when multiple
traces are displayed on the CRT. In mainframes with read-
out, it also replaces the deflection factor readout with the
word "IDENTIFY".
When using a100X readout coded probe such as aP6009
(Tektronix Part No. 010-0264-01), the 7A15A encoding of
CRT readout is incorrect for anumber of VOLTS/DIV
settings. These incorrect readings occur with the MAG
switch in the IX gain position as follows: Actual: 50mV,
10V, 20V and IS, should read: 500mV, 100V, 200V and
IkV. If a100X probe is to be used with the 7A15A at
these sensitivities, in aCRT readout mainframe, it might be
preferable to defeat the probe coding and multiply the
plug-in VOLTS/DIV by afactor of 100 as in non-coded
operation. Possible means for achieving this is; use aP6009
Tektronix Part No. 010-0170-00 (no readout connector),
defeat the probe coding connection in the 7A15A by dis-
connecting R48, defeat the CRT readout entirely for the
7A15A by unsoldering the A37 and B37 cable connections
between the readout EC board and the mainframe EC
board.
APPLICATIONS
General
The following information describes the procedures and
techniques for making measurements with a7A15A/
7A15AN and the associated Tektronix oscilloscope and
time-base. These applications are not described in detail,
since each application must be adapted to the requirements
of the individual measurements. This instrument can also be
used for many applications which are not described in this
manual. Contact your local Tektronix Field Office or
representative for assistance in making specific measure-
ments with this instrument.
Peak-to Peak Voltage Measurements (AC)
To make peak-to-peak voltage measurements, use the
following procedure:
1. Apply the signal to the Input connector.
2. Set the Coupling switch to AC.
NOTE
For low-frequency signals below about 30 hertz, use
the DC position to prevent attenuation of the signal.
3. Set the VOLTS/DIV switch to display about five
vertical divisions of the waveform.
4. Set the time-base Triggering controls for astable
display. Set the Time Base to asweep rate which displays
several cycles of the waveform.
5. Turn the 7A15A/7A15AN 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. 2-1).
6. Measure the divisions of vertical deflection peak to
peak. Check that the VARIABLE control is in the CAL
position.
NOTE
This technique can also be used to make measure-
ments between two points on the waveform, rather
than peak to peak.
7. Multiply the distance measured in step 7by the
VOLTS/DIV switch setting. Include the attenuation factor
of the probe if used.
EXAMPLE: Assume that the peak to peak vertical
deflection is 4.5 divisions using a10X attenuator probe,
and the VOLTS/DIV switch is set to 1V.
REV. B, OCT. 1974 23

Operating Instructions—7A15A/7 A15AN
Fig. 2-1. Measuring the Peak-to-Peak voltage of awaveform.
Volts
vertical
deflection X
(divisions)
VOLTS/D IV
setting Xprobe
attenuator
factor
Substituting the given values:
Volts Peak to Peak =4.5 X1X10
The peak-to peak voltage is 45 volts.
NOTE
To measure avoltage level with respect to another
voltage rather than ground, make the following
changes to Step 3. Set the coupling switch to DC and
apply the reference voltage to the Input connector.
Then position the trace to the reference line and
disconnect the reference voltage.
4.
Set the Coupling switch to DC. The ground reference
line can be checked at any time by switching to the GND
position.
5.
Set the time-base Triggering controls for a stable
display. Set the Time Base sweep rate for an optimum
display of the waveform.
6.
Measure the distance in divisions between the
reference line and the point on the waveform at which the
DC level is to be measured. For example, in Fig. 2-2 the
measurement is between the reference line and point A.
7. Establish the polarity of the waveform. With the
+UP/INV switch in the +UP position, any point above the
reference line is positive.
8. Multiply the distance measured in step 7by the
VOLTS/D IV switch setting. Include the attenuation factor
of the probe, if used.
If you are using a7A15A with acoded probe and an
oscilloscope equipped with readout, simply multiply the
distance measured in step 7by the deflection factor
displayed on the CRT.
EXAMPLE: Assume the vertical distance measured is
4.6 divisions (see Fig. 2-2) and the waveform is above the
reference line using a10X probe with aVOLTS/DIV
switch setting of 0.5 V.
Instantaneous Voltage Measurements (DC)
To measure the DC level at agiven point on awaveform,
proceed as follows:
1. Connect the signal to the Input connector.
2. Set the VOLTS/DIV switch to display about five divi-
sions.
Using the formula:
Instan- vertical VOLTS/ probe
taneous =distance Xpolarity XDIV X attenuation
Voltage (divisions) setting factor
Substituting the given values:
3.
Set the Coupling switch to GND 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.
Instantaneous Voltage -4.6 X1X0.5 VX10
The instantaneous voltage is 23 volts.
2-4 REV. B, OCT. 1974

Operating Instructions—7A15A/7A15AN
Fig. 2-2 Measuring instantaneous voltage with respect to some
reference.
not known, it can be measured before the VARIABLE
control is set in step 2.
4.
Divide the amplitude of the reference signal (volts)
by the product of the vertical deflection (divisions) estab-
lished in step 2and the setting of the VOLTS/DIV switch.
This is the vertical conversion factor.
Vertical
Conversion
Factor
reference signal amplitude (volts)
vertical deflection ^VOLTS/DIV
(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 a setting that provides sufficient vertical deflection to
make an accurate measurement. Do not re adjust the
VARIABLE control.
Comparison Measurements
In some applications it may be desirable to establish
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 facili-
tate calibration of equipment where the desired amplitude
does not produce an exact number of divisions of deflec-
tion. 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 divi-
sions of deflection. The following procedure describes how
to establish arbitrary units of measure for comparison
measurements.
6.
Measure the vertical deflection in divisions and calcu-
late the amplitude of the unknown signal using the
following formula:
Signal =VOLTS/DIV
Amplitude setting
vertical vertical
Xconversion Xdeflection
factor (divisions)
EXAMPLE: Assume areference signal amplitude of 30
volts, aVOLTS/DIV setting of 5Vand the VARIABLE
control adjusted to provide avertical deflection of four
divisions.
To establish avertical deflection factor based upon a
specific reference amplitude, proceed as follows: Substituting these values in the vertical conversion factor
formula (step 4):
1. Connect the reference signal to the Input connector.
Set the time base sweep rate to display several cycles of the
signal. Vertical Conversion
Factor
30 V
4X5V1.5
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
VARIABLE control after obtaining the desired deflection.
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
Then with aVOLTS/DIV setting of 2V, the peak to peak
amplitude of an unknown signal which produces avertical
deflection of five divisions can be determined by using the
signal amplitude formula (step 6):
Signal
Amplitude 2VX1.5 X5=15 volts
REV. B, OCT. 1974 25

7A15A/7A15AN
SECTION 3
CIRCUIT DESCRIPTION
Introduction
This section of the manual contains adescription of the
circuitry used in the 7A15A/7A15AN amplifier. The
description begins with adiscussion of the instrument using
the block diagram shown in the Diagrams section. Then,
each circuit is described in detail using block diagrams 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 following discussion is provided to aid in under-
standing the overall concept of the 7A15A/7A15AN before
the individual circuits are discussed in detail. Only the basic
interconnections between the individual blocks are shown
on the block diagram (see Diagrams section). Each block
represents amajor circuit within the instrument.
The signal to be displayed on the CRT is applied to the
Input connector. The signal passes through the input
coupling switch, where the appropriate coupling is selected,
to the attenuators. The VOLTS/D IV switch selects the
correct amount of attenuation and the signal is passed to
the Input Amplifier.
The Input Amplifier provides signal polarity inversion in
addition to gain setting, variable gain control, and trace
positioning. The output of this circuit is applied push pull
to the Signal and Trigger Amplifiers.
The signal and trigger outputs are provided to the
oscilloscope via the Interface connector.
The Readout encoding circuit (7A15A only) provides
readout logic for the oscilloscope readout system. Logic is
supplied identifying the polarity, deflection factor, and the
uncalibrated symbol (when the VARIABLE knob is not
fully clockwise). When the IDENTIFY button is pressed,
the trace is deflected about 0.3 division and the deflection
factor readout is replaced by the word "IDENTIFY"
(7A15A only).
DETAILED CIRCUIT DESCRIPTION
Attenuator
General
The Attenuator circuit determines the input coupling
and the deflection factor. Adiagram of this circuit is shown
on Diagram 1in the Diagrams section.
AC-GND-DC Switch
Input signals connected to the Input connector can be
AC-coupled, DC-coupled, or internally disconnected.
SI 00Ais acam-type switch; acontact closure chart show-
ing the operation is given on Diagram 1. The dots on this
chart indicate when the associated contacts are in the
position shown (open or closed). When the AC-GND-DC
switch is in the DC position, the input signal is coupled
directly to the Input Attenuator stage. In the AC position,
the input signal passes through capacitor CIO. The
capacitor prevents the DC component of the signal from
passing to the amplifier. The GND position opens the signal
path and connects the input circuit of the amplifier to
ground. This provides aground reference without the need
to disconnect the applied signal from the Input connector.
Resistor R102, connected across the AC-GND-DC switch,
allows CIO to be pre charged in the GND position so the
trace remains on screen when switching to the AC position
if the applied signal has ahigh DC level.
Input Attenuator
The effective overall deflection factor of the 7A15A/
7A15AN is determined by the setting of the VOLTS/DIV
switch, S100B. The basic deflection factor is five millivolts
per division of CRT deflection (with Mag switch set to XI).
To increase the basic deflection factor to the values indica-
ted on the front panel, precision attenuators are switched
into the circuit. S100B is acam-type switch and 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 position, input attenuation is not
used; the input signal is connected directly to the input
amplifier.
REV. B. OCT. 1974 31

Circuit Description—7A15A/7A15AN
For switch positions above five millivolts, the attenua-
tors are switched into the circuit singly or in pair; to pro-
duce the deflection factor indicated on the frort panel.
These hybrid attenuators are frequency-compensated
voltage dividers. For DC and low-frequency signals, the
attenuators are primarily resistance dividers and the voltage
attenuation is determined by the resistance ratio in the
circuit. The reactance of the capacitors in the circuit is so
high at low frequencies that their effect is negligible. How-
ever, at higher frequencies, the reactance of the capacitors
decreases and the attenuator becomes primarily acapaci-
tance divider.
In addition to providing constant attenuation at all
frequencies within the bandwidth of the instrument, the
Input attenuators are designed to maintain the sane input
RC characteristics (one megohm X20 pF) for each setting
of the VOLTS/D IV switch. Each attenuator contains an
adjustable series capacitor to provide correct attenuation at
high frequencies, and an adjustable shunt capacito’ to pro-
vide correct input capacitance.
Input Amplifier
General
The Input Amplifier converts the single-endtd signal
applied to the Input connector to adifferential (pjsh-pull)
output. Aschematic of this circuit is shown on Dagram 2
in the Diagrams section.
Input Source Follower
The Input Source Follower Q210A provides ahigh input
impedance with alow impedance drive for the following
stage. R210 limits the current drive to the gate of Q210A.
Dual-diode CR210 provides circuit protection by limiting
the voltage swing at the gate of Q210A to about ±(positive
or negative) 15 volts. Q210B provides a constant, current
source for Q210A. Q210A and Q210B are encapsjlated in
the same case so that Q210B temperature compensates the
circuit.
Amplifier
The signal from the Input Source Follower is aoplied to
paraphase amplifier Q220-Q320. The paraphase amplifier
converts the single-ended input to adifferential (push-pull)
output. It also provides ameans of compensating for stray
currents throughout the entire amplifier by varying the DC
Level at the base of Q320 via the DC Bal control R322. The
differential signal from the paraphase amplifier is cascoded
to the Inverting Amplifier, aset of common base differen-
tial amplifiers Q230-Q330 and Q235-Q335. With the
POLARITY switch set to +UP, Q230 and Q330 are forward
biased while Q235 and Q335 are reverse biased. The signal
is therefore allowed to pass un-inverted through
Q230-Q330. By setting the POLARITY switch to NVERT,
Q230 and Q330 are reverse biased and Q235 and Q335 are
forward biased. The signal is inverted through Q235-Q335.
Current gain for amplifiers Q230-Q330 and Q235-0335 is
controlled by the GAIN potentiometer R238 and
VARIABLE control R239. The output from Q230-Q330 or
Q235Q335 (depending on the POLARITY switch) is
connected to the XI amplifier, Q240-Q340, and the X10
amplifier. Q245-Q345. The MAG switch determines which
amplifier (XI or X10) is on, by switching their emitter
supply voltages. Current gain for the X10 amplifier is
adjusted by R245. R341 and C341 provide frequency com-
pensation for the XI amplifier. The signal from the XI or
X10 amplifier (depending on the MAG switch) is cascoded
through the common base amplifier, Q250-Q350, to the
Signal Amplifier, Q260-Q360. and Trigger Amplifier,
Q270-Q370.
Connectors and Readout
General
The Connectors and Readout circuit consists of the
power supply and signal distribution from the Interface
Connector and the Readout Encoding circuit. Aschematic
of this circuit is shown on Diagram 3in the Diagrams
section.
Connectors
All the connections made to the mainframe by the
7A15A/7A15AN are shown on the Connectors portion of
Diagram 1. Also shown are the power supply decoupling
components.
Readout Encoding (7A15A only)
The Readout Encoding circuit consists of switching
resistors and probe sensing stage Q620. This circuit encodes
the Row and Column output lines for readout of deflection
factor, uncalibrated deflection factor (VARIABLE) infor-
mation, and signal inversion. Data is encoded on these
output lines by switching resistors between them and the
time slot input lines or by current added through Q620.
R647-C647 are switched between time-slot three (TS-3)
and the Column output line when the CAL switch is in the
uncal position. This results in the symbol >(greater than)
being displayed preceding the deflection factor readout.
R648 is switched between TS-2 and the Column output line
when the POLARITY switch is in the INVERT position.
This results in the symbol f(inverted) being displayed
preceding the deflection factor readout.
Switching resistors are used to indicate the setting of the
VOLTS/DIV switch to the mainframe readout system. The
dots on the contact-closure chart (see Diagram 3) indicate
when the associated contacts on the VOLTS/DIV cam
3-2

Circuit Description 7A15A/7A15AN
switch are closed. R633, R634, and R635 select the
number 1, 2, or 5depending on the 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 1, 2. and 5Vpositions. R630, Rf>31,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 Q620 identifies the attenuation
factor of the probe connected to the Input connector by
sensing the amount of current flowing through the probe
coding resistor located in the probe connector. 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 probr sensing
device 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 Qi520 and
determines the collector current, along with emittei resistor
R622. When the -15 volt time-slot pulse is applied to Inter-
face 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 read-
out is determined by the VOLTS/DIV switch position. With
a10X probe connected, the bias on Q620 allows 100
microamperes of collector current to flow. This increases
the deflection factor readout by afactor of 10.
The IDENTIFY button (S45 on Diagram 1) does two
things when pressed:
1. It causes the trace representing the appropriate
channel of the 7A15A to move.
2. 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 7A15A trace
when multiple traces are displayed. When the IDENTIFY
button is released, the deflection factor readout is restored.
For further information on the operation of the readout
system, see the oscilloscope instruction manual.
REV. B. OCT. 1974 33

SECTION 4
MAINTENANCE
7A15A/7A15AN
Introduction
This section of the manual contains maintenance infor-
mation for use in preventive maintenance, corrective main
tenance, and troubleshooting of the 7A15A/7A15AN.
Further maintenance information relating to general
maintenance can be found in the instruction manjals for
the 7000-series oscilloscopes.
PREVENTIVE MAINTENANCE
General
Preventive maintenance, consisting of cleaning, visual
inspection, etc., performed on a regular basis, will improve
the reliability of this instrument. Periodic checks of the
semiconductor devices used in the unit are not recom-
mended as apreventive maintenance measure. See
semiconductor-checking information given under Trouble-
shooting.
Cleaning
Avoid the use of chemical cleaning agents which
might damage the plastics used in this instrument.
Special care should be taken when cleaning the Poly-
phenylene Oxide attenuator board. Do not apply any
solvent containing ketones, esters or halogenated
hydrocarbons. To dean, use only water soluble
detergents, ethyl, methyl or isopropyl alcohol.
Front Panel. Loose dust may be removed with asoft
cloth or adry brush. Water and mild detergent may be
used; however, abrasive cleaners should not be used.
Interior. Cleaning the interior of the unit should precede
calibration, since the cleaning process could alter the
settings of the calibration adjustments. Use low-velocity
compressed air to blow off the accumulated dust. Hardened
dirt can be removed with asoft, dry brush, cottor -tipped
swab, or cloth dampened with amild detergent and water
solution.
Lubrication
Use acleaning-type lubricant on shaft bushings, inter-
connecting plug contacts, and switch contacts. Lubricate
switch detents with aheavier grease. Alubrication kit con-
taining the necessary lubricating materials and instructions
is available through any Tektronix Field Office. Order
Tektronix Part Number 003-0342-01.
TROUBLESHOOTING
General
The following is provided to augment information
contained in other sections of this manual when trouble-
shooting the 7A15A/7A15AN. The schematic diagrams,
circuit description, and calibration sections should be used
to full advantage. The circuit description section gives
detailed information on circuit behavior and output
requirements.
Troubleshooting Aids
Diagrams. Circuit diagrams are given on foldout pages in
Section 7. The circuit number and electiical value of each
component in this instrument are shown on the diagrams.
Important voltages are also shown.
Circuit Boards. The circuit boards used in the 7A15A/
7A15AN are outlined on the schematic diagrams, and
photographs of the boards are shown on the backs of the
schematic diagrams. Each board-mounted electrical com-
ponent is identified on the photograph by its circuit
number.
Component and Wiring Color Code. Colored stripes or
dots on resistors and capacitors signify electrical values,
tolerances, etc., according to the EIA standard color code.
Components not color coded usually have the value printed
on the body.
The insulated wires used for interconnection in the
7A1 5A/7A1 5AN, are color coded to facilitate tracing wires
from one point to another in the unit.
Semiconductor Lead Configuration. Fig. 41shows the
lead configurations of the semiconductor devices used in
this instrument.
REV. B. OCT. 1974 4-1

Maintenance—7A15A/7A15AN
Fig. 4-1. Electrode configuration for semiconductors in the 7A15A/
7A15AN.
Troubleshooting Equipment
The following equipment is useful for troubleshooting
the 7A15A/7A15AN.
Troubleshooting Procedure
This troubleshooting procedure is arranged in an order
which checks the simple trouble possibilities before
proceeding with extensive troubleshooting.
1. Check Control Settings. An incorrect setting of the
7A15A/7A15AN controls can indicate atrouble that does
not exist. If there is any question about the correct func-
tion or operation of acontrol or front-panel connector, see
the Operating Instructions section.
2. Check Associated Equipment. Before proceeding
with troubleshooting of the 7A15A/7A15AN, check that
the equipment used with this instrument is operating
correctly. If possible, substitute an amplifier unit known to
be operating correctly into the indicator unit and see if the
problem persists. Check that the input signals are properly
connected and that the interconnecting cables are not
defective.
3. Visual Check. Visually check the portion of the
instrument in which the trouble is suspected. Many troubles
can be located by visual indications, such as unsoldered
connections, broken wires, damaged circuit boards,
damaged components, etc.
4. Check Instrument Performance. Check the calibra-
tion of the unit or the affected circuit, by performing
Performance Check of Section 5. The apparent trouble may
only be aresult of mis-adjustment, and may be corrected
by calibration. Complete calibration instructions are given
in Part II of Section 5.
1. Semiconductor Tester—Some means of testing the
transistors, diodes, and FET's used in this instrument is
helpful. Atransistor-curve tracer such as the Tektronix
Type 576 will give the most complete information.
2. DC Voltmeter and Ohmmeter—Avoltmeter is
required for checking voltages within the circuits, and an
ohmmeter for checking resistors and diodes.
3.
Test Oscilloscope—Atest oscilloscope is required to
view waveforms at different points in the circuit. A
Tektronix 7000-series Oscilloscope equipped with areadout
system, 7D13 Digital Multimeter unit, 7B-series Time-Base
unit, and a7A-series Amplifier unit with a10X probe will
meet the needs of both items 2and 3.
4.
Plug-in Extender—Afixture that permits operation of
the unit outside of the plug-in compartment for better
accessibility during troubleshooting. Order Tektronix part
number 067-0589-00.
5. Check Voltages. Often the defective component or
stage can be located by checking for the correct voltage in
the circuit. Typical voltages are given on the diagrams; how-
ever, these are not absolute and may vary slightly between
instruments. To obtain operating conditions similar to
those used to take these readings, see the instructions in the
Diagrams section.
6. Check Individual Components. The following
methods are provided for checking the individual com-
ponents in the 7A15A/7A15AN. Components which are
soldered in place are best checked by disconnecting one end
to isolate the measurement from the effects of surrounding
circuitry.
NOTE
To locate intermittent or temperature sensitive com-
ponents mounted on the attenuator board, Quik
Freeze (Miller Stephenson, MS-240, Tektronix Part
Number 006-0173-011 is recommended. Dry ice or
dichlorodi-fluorremethane (Freon 12, Dupont or Can-
O-Gas) may also be used. Other types of circuit
coolant may damage the polyphenylene oxide boards.
4-2

Maintenance—7A1 5A/7A1 5AN
A. TRANSISTORS. The best check of transistor opera-
tion is actual performance under operating conditions. If a
transistor is suspected of being defective, it can best be
checked by substituting acomponent known to be good;
however, be sure that circuit conditions are not such that a
replacement might also be damaged. If substitute transistors
are not available, use adynamic tester (such as Tektronix
Type 576). Static-type testers may be used, but since they
do not check operation under simulated operating condi-
tions, some defects may go unnoticed. Fig. 4-1 shows base
pin and socket arrangements of semiconductor devices. Be
sure the power is off before attempting to remove or
replace any transistor.
B. DIODES. Adiode can be checked for an open or for
ashort circuit by measuring the resistance between termi-
nals with an ohmmeter set to the RXIk scale. The diode
resistance should be very high in one direction and very low
when the meter leads are reversed. Do not check tunnel
diodes or back diodes with an ohmmeter.
Do not use an ohmmeter scale that has a high internal
current. High currents may damage the diodes.
C. RESISTORS. Check resistors with an ohmmeter.
Resistor tolerance is given in the Electrical Parts List.
Resistors normally do not need to be replaced unless the
measured value varies widely from the specified value.
D. CAPACITORS. Aleaky or shorted capacitor can be
detected by checking resistance with an ohmmeter on the
highest scale. Use an ohmmeter which will not exceed the
voltage rating of the capacitor. The resistance reading
should be high after initial charge of the capacitor. An open
capacitor can best be detected with acapacitance meter, or
by checking whether the capacitor passes AC signals.
7. Repair and Readjust the Circuit. Special techniques
required to replace components in this unit are given under
Component Replacement. Be sure to check the perform-
ance of any circuit that has been repaired or that has had
any electrical components replaced. Recalibration of the
affected circuit may be necessary.
CORRECTIVE MAINTENANCE
General
Corrective maintenance consists of component replace-
ment and instrument repair. Special techniques required to
replace components in this instrument are given here.
Obtaining Replacement Parts
Standard Parts. All electrical and mechanical part
replacements for the 7A15A/7A15AN can be obtained
through your local Tektronix Field Office or representative.
However, many of the electronic components can be
obtained locally in less time than is required to order them
from Tektronix, Inc. Before purchasing or ordering replace-
ment parts, check the parts list for value, tolerance, rating
and description.
NOTE
When selecting replacement parts, it is important to
remember that the physical size and shape of acom-
ponent may affect the performance of the instru-
ment, particularly at high frequencies. AH replace-
ment parts should be direct replacements unless it is
known that adifferent component will not adversely
affect instrument performance.
Special Parts. In addition to the standard electronic
components, some special parts are used in the 7A15A/
7A15AN. These parts are manufactured or selected by
Tektronix, Inc. in accordance with our specifications. These
special parts are indicated in the parts list by an asterisk
preceding the part number. Most of the mechanical parts
used in this instrument have been manufactured by
Tektronix. Inc. Order all special parts directly from your
local Tektronix Field Office or representative.
Ordering Parts. When ordering replacement parts from
Tektronix, Inc., include the following information:
1. Instrument Type.
2. Instrument Serial Number.
3. Adescription of the part (if electrical, include circuit
number).
4. Tektronix Part Number.
Soldering Techniques
WARNING
Disconnect the instrument from the power source
before soldering.
Attenuator Circuit Board. The Attenuator circuit board
is made from polyphenylene oxide because of its excellent
electrical characteristics. Use more than normal care when
cleaning or soldering this material. The following rules
should be observed when removing or replacing parts:
REV. C. MAR. 1975 4-3

Maintenance—7A15A/7A15AN
1. Use alow-wattage soldering iron (not over 15 watts).
2. Do not apply more heat, or apply heat for alonger
time, than is absolutely necessary.
3. Use some form of vacuum solder remover when
removing multi-lead devices.
4. Do not apply any solvent containing ketones, esters
of halogenated hydrocarbons.
5. To clean, use only water-soluble detergents, ethyl,
methyl or isopropyl alcohol.
Circuit Boards (except Attenuator board). The com-
ponents mounted on the circuit boards in the amplifier can
be replaced using normal circuit board soldering techniques.
Keep the following points in mind when soldering on the
circuit boards:
1.
Use apencil-type soldering iron with a(wattage)
rating from 15 to 50 watts.
2. Apply heat from the soldering iron to the junction
between the component and the circuit board.
3. Heat-shunt the lead to the component by means of a
pair of long-nose pliers.
4. Avoid excessive heating of the junction with the
circuit board, as this could separate the circuit board wiring
from the base material.
5. Use electronic grade 60-40 tin lead solder.
6. Clip off any excess lead length extending beyond the
circuit board. Clean off any residual flux with aflux-
removing solvent.
Metal Terminals. When soldering metal terminals
(potentiometers, etc.) use 60-40 tin-lead solder and a15 to
50 watt soldering iron. Observe the following precautions
when soldering metal terminals:
1. Apply only enough heat to make the solder flow
freely.
2. Apply only enough solder to form asolid connection.
Excess solder may impair the function of the part.
3. If awire extends beyond the solder joint, clip off the
excess.
4. Clean the flux from the solder joint with aflux-
removing solvent.
Component Replacement
Disconnect the equipment from the power source
before replacing components.
Semiconductor Replacement. Transistors should not be
replaced unless actually defective. If removed from their
sockets during routine maintenance, return them to their
original sockets. Unnecessary replacement of transistors
may effect the calibration of this instrument. When tran-
sistors are replaced, check the performance of the part of
the instrument which may be affected.
Replacement semiconductors should be of the original
type or a direct replacement. Fig. 41shows the lead con-
figurations of the semiconductors used in this instrument.
If the replacement semiconductor is not of the original
type, check the manufacturer's basing diagram for proper
basing.
Circuit Board Removal
In general, the circuit boards used in the 7A15A/
7A15AN need never be removed unless they must be
replaced. Electrical connections to the boards are made by
soldered connections. If it is necessary to replace acircuit
board assembly, use the following procedures.
A. READOUT CIRCUIT BOARD REMOVAL (7A15A
Only)
1. Disconnect the wires connected to the outside of the
board.
2. Remove the seven screws holding the board to the
mounting surface.
3. Disconnect the wires connected to the inside of the
board.
4. Remove the board from the unit.
5. To replace the board, reverse the order of removal.
4-4

Maintenance—7A15A/7A15AN
B. ATTENUATOR CIRCUIT BOARD REMOVAL
1. Remove the readout board as outlined in the previous
procedure.
2. Disconnect the resistor and capacitor connected to
the rear of the board.
3. Loosen the front set screw on the VARIABLE con-
trol shaft coupling (use a0.050-inch hex-key wrench).
4. Remove the red VARIABLE control knob and glass
rod from the control shaft.
5. Remove the remaining front-panel knobs using a
1/16-inch hex-key wrench.
6. Remove the front panel from the instrument.
7. Remove the attenuator shields.
8. Disconnect the wires and resistor from the input BNC
connector.
9. Remove the input BNC connector.
10. Remove the attenuator board with cam switch from
the instrument.
11. Replace by reversing the Removal Procedures.
C. AMPLIFIER CIRCUIT BOARD REMOVAL
1. Remove the plastic plug-in guide from the rear of the
instrument.
2. Disconnect the wires connected to the board from
the front-panel controls.
3. Loosen the hex-socket screw in the coupling of the
VARIABLE control shaft using a0.050-inch hex-key
wrench. Pull the VARIABLE knob and glass shaft from the
front of the instrument.
4. Disconnect the resistor-capacitor combinations
connected to the ceramic strip at the front of the board.
5. Remove the screws and nuts securing the board to
the chassis or other mounting surface.
6. Remove the board from the instrument.
7. To replace, reverse the order of removal.
Switch Replacement
Several types of switches are used in the 7A15A/
7A15AN. The slide and micro switches should be replaced
as aunit if damaged. The following special maintenance
information is provided for the cam-type switches.
A. CAM-TYPE SWITCHES
Repair of cam-type switches should be undertaken
only by experienced maintenance personnel. Switch
alignment and spring tension of the contacts must be
carefully maintained for proper operation of the
switch. For assistance in maintenance of the cam-type
switches, contact your local Tektronix Field Office or
representative.
Recalibration After Repair
After any electrical component has been replaced, the
calibration of that particular circuit should be checked, as
well as the calibration of other closely related circuits.
Refer to Section 5for these procedures.
4-5

7A15A/7A15AN
SECTION 5
CALIBRATION
Introduction
To assure instrument accuracy, check the calibration of
the 7A15A/7A15AN every 1000 hours of operation or
every six months if used infrequently. Before complete cali-
bration, thoroughly clean and inspect this instrument as
outlined in the Maintenance section.
Tektronix Field Service
Tektronix, Inc., provides complete instrument repair and
recalibration service at local Field Service Centers and the
Factory Service Center. Contact your local Field Office or
representative for further information.
Using This Procedure
General. This section provides several features to facili-
tate checking or adjusting the 7A15A/7A15AN. These are:
Short Form Procedure. As an aid to the calibration of
this instrument, ashort form procedure is given prior to the
complete procedure. To facilitate instrument calibration for
the experienced calibrator, the short form procedure lists
the calibration adjustments necessary for each step and the
applicable tolerances.
Partial Calibration Procedure. Apartial calibration is
often desirable after replacing components, or to touch up
the adjustment of aportion of the instrument between
major recalibrations. To calibrate only part of the instru-
ment, set the controls as given under Preliminary Control
Settings and start with the nearest numbered step preceding
the desired portion. To prevent unnecessary recalibration of
other parts of the instrument, readjust only if the tolerance
given in the CHECK— part of the step is not met.
Complete Calibration Procedure. Completion of each
step in the Calibration Procedure insures that this instru-
ment meets the electrical specifications given in Section 1.
Where possible, instrument performance is checked before
an adjustment is made. For best overall instrument per-
formance when performing acomplete calibration
procedure, make each adjustment to the exact setting even
if the CHECK— is within the allowable tolerance.
TEST EQUIPMENT REQUIRED
General
The following test equipment and accessories, or its
equivalent is required for complete calibration of the
7A15A/7A15AN. Specifications given for the test equip-
ment are the minimum necessary for accurate calibration.
Therefore, some of the specifications listed here may be
somewhat less precise than the actual performance
capabilities of the test equipment. All test equipment is
assumed to be correctly calibrated and operating within the
listed specifications of the recommended equipment.
Test Equipment
1. Calibration Oscilloscope. Tektronix 7704 or equiva-
lent 7000-series Oscilloscope.
2. 7B-Series Time Base plug-in unit.
31 .Standard Amplitude Calibrator. Amplitude
accuracy, within 0.25%; signal amplitude, 5millivolts to 50
volts; frequency. 1kHz. Tektronix Calibration Fixture
067-0502-01 recommended.
4J.Square-wave Generator. Must have the following
output capabilities: 12 volts amplitude into 50 ohms at one
kilohertz with arise time of 12 nanoseconds or less; 500
millivolts into 50 ohms at 100 kilohertz with arisetime of
one nanosecond or less. Tektronix Type 106 Square-Wave
Generator recommended.
Accessories
5. Cable. Impedance, 50 ohms; connector, BNC; length,
42 inches. Tektronix Part Number 011-0060-01.
62 .Five nanosecond GR cable. Tektronix Part Number
017-0512-00.
1Needed for Gain Calibration only.
2Needed for Compensation adjustments only.
5-1