Tektronix 7a15 User manual

,
INSTRUCTION
MANUAL
Seriol Number ___ __ _
7A15
AMPLIFIER
Tektronix, Inc .• P. O. Box 500 • Beoverton, Oregon 97005 • Phone [phone] • Coble~: Tektronil!.
070· '044 ·00
670

7A15
WARRANTY
;JlIiII"'ionu are warranted against
oti wo!'krMmhip for OM 'INf •
..... ~ ..... ufKturad in our plant,
~ the instrument.
"'oa';o,,, and price change privileges reserved.
Copyright @
1970 by Tektronix, Inc., Beaverton,
Oregon. Printed in the United States of America. All
,ights reserved. Contents of this publication may not
be reproduced in any form without permission of the
copyright owner.
U.S.A. and fotttign Tektronix products covered
by U.S. and foreign patents and/or patents pending_
®

SECTION 1
SECTION 2
SECTION 3
SECTION 4
®
7A15
TABLE OF CONTENTS
Page Page
SPECIFICATION SECTION 5 PERFORMANCE CHECK/CALIBRATION
Introduction
1-1
I ntrod uction 5-1
Electrical Characteristics
1-1
Test Equipment Required 5-1
Environmental Characteristics 1-2
Short-Form Procedure and Index 5-2
Physical Characteristics 1-2 Performance Check/Calibration
Procedure 5-4
OPERATING INSTRUCTIONS
General
2-1
SECTION 6 ELECTRICAL PARTS LIST
Installation
2-1
Abbreviations and Symbols
Front-Panel Controls
2-1
Parts Ordering Information
First Time Operation
2-1
Index of Electrical Parts list
Control Setup Chart
2-2
General Operating Information 2-4
Basic Applications 2-5 SECTION 7 DIAGRAMS AND MECHANICAL PARTS
IllUSTRATIONS
Mechanical Parts Illustrations
CIRCUIT DESCRIPTION
Instrument Repackaging
Introduction
3-1
Block Diagram Description 3-1
Detailed Circuit Description 3-1
SECTION 8 MECHANICAL PARTS LIST
MAINTENANCE Mechanical Parts List Information
Index
of Mechanical Parts Illustrations
Introduction
4-1 Mechanical Parts
list
Preventive Maintenance 4-1 Accessories
Troubleshooting 4-2
Corrective Maintenance 4-5
Instrument Repackaging 4-8 CHANGE INFORMATION
Abbreviations and symbols used
in this manual are based on or taken directly from IEEE
Standard 260 "Standard Symbols for Units", MIL-STD-12B and other standards of the
electronics industry. Change information, if any, is located at the rear of this manual.

7A15
• •• •
::I tHYEIIT
AMPLIFieR
®

7A15
SECTION 1
SPECIFICA TION
Change information, if any, affecting this section will be found at the rear of the manual.
Introduction
The 7A15 vertical amplifier plug-in unit is designed for
use with
Tektronix 7000-series Oscilloscopes. The 7A 15 is a
wideband general purpose amplifier,
with the upper fre-
quency limit determined mainly by
the oscilloscope in
which it is used. For example, the 7A15 used with the 7504
oscilloscope will have a System Bandwidth of 60 mega-
hertz; and
when used with the 7704 oscilloscope, the
system bandwidth will be 75 megahertz. A POLARITY
switch provides a means of inverting the display. The 7A15
can be operated
in any plug-in compartment of the 7000-
series oscilloscopes.
This instrument will
meet the electrical characteristics
listed
in Table 1-1 following complete calibration as given
in Section 5. The performance check procedure given in
Section 5 provides a convenient method of checking instru-
ment performance without making internal adjustments.
The following electrical characteristics are valid over the
stated environmental range for instruments calibrated at an
ambient temperature of +20°C to +30
oC, and after a five
minute warmup unless otherwise noted.
TABLE 1-1
ElECTRICAL CHARACTERISTICS
Characteristic
Deflection
Factor
Calibrated Range
Gain Ratio
Accuracy
Uncalibrated
(Variable)
GAIN
®I
Performance
5 mV/div
to 5 V/div; 10 steps in a
1, 2, 5 sequence.
Within 2% of GAIN adjusted at 10
mV/div.
Continuously variable between cali-
brated steps; extends deflection
factor to at least 12.5 V/div.
Permits adjustment of deflection
factor for all 7000-series oscillo-
scopes.
Characteristic
Frequency Response
System
Dependent
Upper Bandwidth
(DC Coupled)
Lower Bandwidth
(AC Coupled)
Without Probe
With
P6053 Probe
Maximum
Input
Voltage
Input Rand C
Resistance
Capacitance
Rand C Product
Maximum Input
Gate Current
Displayed Noise
(Tangentially
Measured)
DC Drift
Drift With Time
(Ambient Tem-
perature and
Line Voltage
Constant)
Short Term
TABLE
1-1 (contI
Performance
7500-series 7700-series
Oscilloscope Oscilloscope
60 MHz 75 MHz
2
hertz or less
0.2 hertz or less
500 V (DC + Peak AC) . AC com-
ponent 1 kHz or less.
1 megohm
within 2%
20 picofarads within 1.5 picofarad
Within 1% over all deflection factor
settings
0.5
nanoampere
or
less, O°C to
+35°C.
2 nanoampere
or less, +350C to
+50
o
C.
0.06 division
or less at 5 mV/div
measured
in
7700-series oscillo-
scope.
250 m icrovoltslminute (P-P)
or
0.05 division (whichever is greater)
in anyone minute, after one hour
warmup.
1-1

Specification-7 A 15
TABLE 1-1 (cont)
Characteristic Performance
Long Term
250 microvolts/hour (P-P) or 0.05
division (whichever
is greater) in
anyone hour, after one hour
warmup.
Drift With
100 microvolt/degree centigrade or
Ambient Tem- less.
perature (Line
Voltage
Constant
1-2
TABLE 1-2
ENVIRONMENTAL CHARACTERISTICS
Refer
to the Specification for the associated oscilloscope.
TABLE 1-3
PHYSICAL
Fits
all 7000-series plug-in compartments.
®

7A15
SECTION 2
OPERA TING INSTRUCTIONS
Change information, if any , affecting this section will be found at the rear of this manual.
General
The 7A15 vertical plug-in units operates with a Tek-
tronix 7000-series oscilloscope and a
7B __ series time-base
unit to form a complete oscilloscope system. To effectively
use the 7A15, the operation and capabilities of the instru-
ment should be known. This section describes the operation
of the front-panel controls, gives first-time operation and
general operating information, and lists some measurement
techniques u'sing
the amplifier.
Installation
The 7A15 is designed to operate in a vertical plug- in
compartment of Tektronix 7000-series oscilloscopes. For
X-Y operation, the 7A 15 may also be installed in a horizon-
tal plug-in
compartment (refer to the Oscilloscope Instruc-
tion Manual for information
on X-Y operation). To install
the 7A15 into a plug-in compartment, push it in until it is
seated flush against the front panel of the oscilloscope. To
remove, pull the release latch to disengage the 7A15 from
the oscilloscope. Continue to pull the release latch to re-
move
the unit from the oscilloscope.
FRONT PANEL CONTROLS
All controls required for operation of the 7A15 are lo-
cated
on the front panel of the unit. A brief description of
the function or operation of the front panel controls
follows. More detailed information is given under General
Operating Information.
VOLTS/DIV
VARIABLE
(VOLTS/DIV)
POSITION
®
Selects calibrated vertical deflection
factor from 5 mV/div to 5 V/div in
a 1, 2, 5 sequence.
Provides uncalibrated variable de-
flection factors. Extends the
highest deflection factor to at least
12.5 V/div. Push
knob in and re-
lease
to activate; the knob moves
outward from the VOLTS/DIV
control when activated.
Controls vertical position
of oscillo-
scope display.
IDENTIFY
POLARITY
+UP
INVERT
COUPLING
AC
GND
DC
GAIN
Adjustment
VAR BAL
Adjustment
INPUT
Connector
General
When pressed, deflects trace up·
ward for identification and changes
CRT readout to the word
"IDENTIFY".
A positive-going signal at the IN-
PUT produces a positive deflection
on the CRT.
Inverts display. A negative-going
signal
at the INPUT produces a
positive deflection
on the CRT.
Capacitively couples the input sig-
nal
to the vertical amplifier.
Disconnects
the input signal from
the amplifier and grounds the am·
p I if ier input. Allows the input
coupling capacitor to be charged to
the DC voltage applied to the IN-
PUT connector.
The signal is directly coupled to the
amplifier.
Screwdriver adjustment permits
calibration of deflection factor.
Screwdriver adjustment permits
balancing of the amplifier for
minimum trace shift while rotating
the VARIABLE control.
BNC connector for applying exter-
nal signals.
FIRST-TIME OPERATION
When shipped from the factory, the 7A15 has been cal i-
brated to meet the specifications listed in Section 1 and is
ready to be used with an indicator oscilloscope.
2-1

Operating Instructions-7A 15
The following steps demonstrate the basic operation of
the controls of the 7A15. It is recommended that this pro-
cedure be followed completely for familiarization with the
instrument. Operation of the oscilloscope and time-base
unit is described in the instruction manual for these units.
Setup Information
1. Insert the 7A 15 into a vertical plug-in compartment
of a 7000-series oscilloscope.
2. Insert a 7B
__ series time-base unit into a horizontal
plug·in compartment.
3. Set the controls as follows:
7A15 (Left Vert compartment)
POSITION Midrange
POLARITY +UP
VOLTS/DIV 10 mV
COUPLING
DC
VARIABLE CAL IN
7B51 (B Horiz compartment)
Level/Slope Centered on positive slope
Triggering
Mode
Coupling
Source
Time/Div
Variable (Time/Div)
Magnifier
B Delay Mode
Position
p.p Auto
AC
Int
1 ms
Cal In
Xl
Independent
Midrange
7504 (Indicator Oscilloscope)
Vertical Mode
Left
Horizontal Mode B
B Intensity
CCW
Calibrator 1 kHz, 40 mV
B Trigger
Source Left Vert
4. Connect the oscilloscope to a power source which
meets the voltage and frequency requirements of the oscil-
loscope power supply.
5. Turn the oscilloscope power on and allow about 5
minutes warmup.
6. Advance the B Intensity until a free·running trace is
observed. Adjust the Position controls to center the trace
on the CRT.
2-2
Lf.
OOJlI
R
,
Fig. 2-1. Oscilloscope display when checking amplifier Gain.
7. Connect the Calibrator output to the 7A 15 INPUT
connector.
8. Check the CRT display for four divisions of vertical
deflection (see Fig. 2-1). If necessary, adjust the front panel
GAIN
for four divisions of vertical deflection.
9. Press the IDENTIFY button and check that the dis-
play moves upward
about 0.3 divisions. Also check that the
readout information on the CRT is replaced by the word
"IDENTI FY".
10. Press and release the VARIABLE control to its out-
ward position. Turn the VAR IABLE control fully counter·
clockwise, and check for 1.6 divisions or less display ampli·
tude. Press the VARIABLE control to the CAL IN position.
11. Change the VOLTS/DIV to 0.1 V, Calibrator Volts
to 0.4 V and the Triggering Source to Ext. Connect the
Calibrator output through a "T" connector to the time base
Ext Trig In and the 7A15 INPUT connector. Set the
POLARITY switch to INVERT to display the opposite
polarity of the square wave.
This completes the basic operating procedure for the
7A15. I nstrument operations not explained here or opera·
tions which need further explanation are discussed under
General Operating Information.
CONTROL SETUP CHART
Figure 2-2 shows the front panel of the 7A15. This chart
can be reproduced and used as a front panel record for
special measurements, applications or procedures, or it may
be used as a training aid for familiarization with this instru-
ment.

NOTES:
®
7A15 TEST SET-UP CHART
O£J ~~:1J'D~,(Y
POSITION
cg
VAR BAL
~
INPUT
1 Mn
20pF
POLARITY
B+UP
INVERT
[!Dm
(@
AC
GND
DC
AMPLIFIER
Fig. 2-2. 7A15 control setup chart.
Operating I nstructions-7 A15
2-3

Operating I nstructions-7 A15
GENERAL OPERATING INFORMATION
Signal Connection
In general, probes offer the most convenient means of
connecting a signal
to the input of the 7A15. Tektronix
probes are shielded
to prevent pickup of electrostatic inter-
ference. A
lOX attenuator probe offers a high input im-
pedance and allows the circuit under test to operate very
close
to normal operating conditions. However, a lOX
probe also attenuates the input signal ten times.
In high-frequency applications requiring maximum over-
all bandwidth, use a coaxial cable terminated
at both ends
in the characteristic impedance of the cable. To maintain
the high-frequency characteristics of the applied signal, use
high-quality low-loss cable. Resistive coaxial
attenuators
can be used to minimize reflections if the applied signal has
suitable amplitude.
High-level low-frequency signals can be connected direc-
tly to
the 7A15 INPUT connector with short unshielded
leads using a
BNC to Banana Jack Adapter. This method
works best for signals below about one kilohertz and deflec·
tion factors above
one volt/division. When this method is
used, establish a common ground between the 7A15 and
the equipment under test (common ground provided by
line cords
is usually inadequate). Attempt to position the
leads away from any source of interference to avoid errors
in the display. If interference is excessive with unshielded
leads, use a coaxial cable
or a probe.
I nput Coupling
The AC-GND-DC lever switch allows a choice of input
coupling. The type of display desired determines the mode
of input coupling used. The DC position can be used for
most applications. However, if the DC component of the
signal is much larger than the AC component, the AC
position will probably provide a better display. DC coupling
should be used
to display AC signals below about 2 hertz
and square waves containing low-frequency
components, as
they will be attenuated in the AC position.
In
the AC position, the DC component is blocked by a
capacitor
in the input circuit. The low-frequency response
in the AC position is about 2 hertz (-3 dB point). There-
fore, some low-frequency
attenuation can be expected near
this frequency limit. Distortion will also appear
in square
waves which have low-frequency components.
The GND position provides a ground reference at the
amplifier input. The signal applied to the INPUT connector
is presented with a one megohm load, while the amplifier
input is grounded. This eliminates the need to externally
ground
the INPUT to establish a DC ground reference.
2-4
The GND position is also used to pre-charge the coupling
capacitor
to the average level of the signal applied to the
INPUT connector. The pre-charge network allows the input
coupling capacitor to charge to the DC source voltage level
when
the COUPLING switch is set to GND.
The procedure for using this feature is as follows:
1. Before connecting
the signal containing a DC com-
ponent to the 7A15 INPUT, set the COUPLING switch to
GND. Then connect the signal to the INPUT connector.
2. Allow
about two seconds for the coupling capacitor
to charge.
3. Reset
the COUPLING switch to AC. The trace
(display) will remain on
the screen and the AC component
of the signal can be measured in the normal manner.
Deflection Factor
The amount of vertical deflection produced by a signal is
determined by the signal amplitude, the attenuation factor
of the probe (if any), the setting of the VOLTS/DIV switch
and
the setting of the VAR IABLE control (if control is in
the outward position). The calibrated deflection factors in-
dicated by the VOLTS/DIV switch apply only when the
VARIABLE control is in the inward (CAL IN) position.
The VAR IABLE control provides uncalibrated vertical
deflection between
the calibrated settings of the VOL TS/
DIV switch, and extends the maximum deflection factor to
at least 12.5 volts/division.
The GAIN control, a front-panel screwdriver adjustment,
sets
the gain of the 7A15 in the 10 mV/div position of the
VOLTS/DIV switch. The gain calibration of the unit should
be checked for accuracy prior
to making critical measure-
ments, using either
the oscilloscope calibrator output or a
standard amplitude calibrator. If
adjustment is necessary,
the GAIN should be adjusted with the VOLTS/DIV switch
set to 10 mY.
Variable Balance
To check and/or adjust the VAR BAL, proceed as fol-
lows:
1.
Set the COUPLING to GND and adjust the time-base
controls for a free-running trace.
2. Press and release
the VAR IABLE control to its out-
ward position.
®

3. While rotating the VARIABLE control throughout its
range, adjust
the VAR BAL (a front panel screwdriver ad-
justment) for minimum trace shift (0.5 div or less shift
as
VARIABLE control is turned from fully clockwise to fully
counterclockwise).
Signal Polarity
The POLAR ITY switch provides a means of inverting
the display. With the POLAR ITY set to +UP, a positive-
going voltage
at the INPUT produces an upward deflection
of the CRT display. With POLARITY set to INVERT, a
positive-going voltage at the INPUT will produce a down-
ward deflection of the CRT display.
If a symmetrical wave-
form such as
the calibrator square-wave is to be observed,
the time-base must be triggered externally to observe the
polarity inversion. This
is due to the time-base unit trigger-
ing on the indicated slope of the displayed waveform when
it
is triggered internally.
Display Identification
When the 7A15 IDENTIFY button is pressed, the CRT
display representing the output of the 7A15 is deflected
upward
about 0.3 division for identification. This feature is
particularly useful in oscilloscopes having multi-trace dis-
plays.
When using an oscilloscope system equipped with
the
readout feature, information such as polarity, deflection
factor, etc., is displayed on the CRT. When the IDENTIFY
button is pressed, the readout information pertaining to the
7A15 is replaced by the word "IDENTIFY" to aid in locat-
ing the 7A15 readout when more than one vertical unit is
used.
BASIC APPLICATIONS
The following information describes the procedure
and techniques for making basic measurements with
the
amplifier. These applications are not described in detail
since each application must be adapted
to the requirements
of the individual measurement. Familiarity with the 7A15
will permit these basic techniques
to be applied to a wide
variety
of uses.
Peak-to-Peak Voltage Measurement-AC
To make a peak-to-peak voltage measurement, use the
following procedure:
1. With
the COUPLING set to GND, connect the signal
to the INPUT connector.
®
Operating Instructions-7A15
If 01 , R
00"
h f1
" 1\ " " {
\ I I \
IJ
\ \
I
\1
V J
\,
V J
Fig. 2-3. Oscilloscope display when making poP voltage measure-
ments.
2. Reset the COUPLING to AC, adjust the time-base
triggering controls for a stable display and set the Time/Div
to display several cycles of the waveform.
3.
Set the VOLTS/DIV switch to display about five
vertical divisions of
the waveform. Check that the VAR-
IABLE control
is in the CAL IN (pushed in) position.
4. With
the POSITION control, position the display so
the lower portion of the waveform coincides with one of
the graticu Ie lines below the center horizontal reference
line, and
the top of the waveform is in the viewing area.
Move the display with the horizontal Position control so
one of the upper peaks is iigned with the center vertical
reference line (see Fig. 2-3).
5. Measure
the vertical deflection from peak to peak
(divisions).
NOTE
This technique may also be used to make measure-
ments between two points on the waveform, rather
than peak to peak.
6. Multiply the distance (in divisions) measured in step
5 by
the VOLTS/DIV switch settings. Include the attenua-
tion factor
of the probe being used.
Example: Assume a peak-to-peak vertical deflection
of 4.6
divisons using a
lOX attenuator probe and a VOLTS/DIV
setting of
0.5 V.
2-5

Operating Instructions-7A15
Volts
(peak-to-peak)
vertical
deflection
(d ivisions)
VOLTS/DIV
X switch X
setting
Substituting
the given values:
Volts (peak-to-peak) = 4.6 X 0.5 X 10
The peak-to-peak voltage is 23 volts.
probe
attenuation
factor
Instantaneous Voltage Measurement-DC
To measure the DC level at a given point on a waveform,
use
the following procedure:
1. Set the COUPLING to GND and position the trace to
the bottom line of the graticule (or other selected reference
line). If
the voltage to be measured is negative with respect
to ground, position the trace to the top line of the grati-
cule. Do not move the vertical POSITION control after this
reference has been established.
NOTE
To measure a voltage level with respect to a voltage
other than ground , make the following changes to
step 1: Set the COUPLING to DC and apply the
reference voltage to the
INPUT connector, then
position the trace to the reference line.
2. Connect the signal to the INPUT connector.
3.
Set the COUPLING to DC (the ground reference can
be checked
at any time by setting the COUPLING to
GND).
4.
Set the VOLTS/DIV switch to display about five ver-
tical divisions
of the waveform. Check that the V AR lAB LE
control is in the CAL IN position. Adjust the time-base
triggering controls for a stable display.
5. Measure the vertical 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. 2-4 the
measurement is made between the reference line and point
A.
6. Establish the polarity of the signal. If the waveform is
above the reference line, the voltage is positive; below the
reference line, negative.
2-6
l R
Point A
Vertical
Distance
Ref
Tence,Line
Fig. 2-4. Oscilloscope display when measuring instantaneous DC
level.
7. Multiply the distance measured in step 5 by the
VOLTS/DIV switch setting. Include the attenuation factor
of the probe, if any. Example: Assume that the vertical
distance measured
is 4.8 divisions, the waveform is above
the reference line, using a lOX attenuator probe and a
VOLTS/DIV switch setting of 0.5 V.
Using
the formula:
Instantaneous
Voltage
vertical
distance X
(divisions)
Polarity
Polarity
Substituting
the given values:
VOLTS/DIV probe
X Switch X
attenuation
setting factor
Instantaneous Voltage =
4.8 X +1 X 0.5 V X 10
The instantaneous voltage is +24 volts.
Voltage Comparison Measurements
In some applications, it may be necessary to establish a
set of deflection factors
other than those indicated by the
VOLTS/DIV switch. This is useful for comparing signals to
a reference signal amplitude. To establish a new set of de-
flection factors based upon a specific reference amplitude,
proceed as follows:
1. Apply a reference signal of known amplitude
to the
INPUT connector. Using the VOLTS/DIV switch and the
VARIABLE control, adjust the display for an exact number
of divisions. Do
not move the VARIABLE control after
obtaining the desired deflection.
2. Divide
the amplitude of the reference signal (volts)
by
the product of the deflection (divisions) from step 1 and
the VOLTS/DIV switch setting. This is the Deflection Con-
version Factor.
®

Deflection
Conversion
Factor
reference signal amplitude (volts)
deflection (divisions) X
VOL TS/DIV setting
3.
To determine the amplitude of a signal compared to a
reference, disconnect the reference signal
and apply the sig-
nal to be compared to the 7A15 INPUT connector.
4. Set the
VOL TS/DIV switch to a setting that provides
sufficient deflection
to make the measurement (do not
readjust the VARIABLE control).
5.
To establish an Adjusted Deflection Factor at any
setting
of the VOL TS/DIV switch, multiply the VOLTS/
DIV switch setting by the Deflection Conversion Factor
established in step
2.
VOL TS/DIV Deflection
Adjusted Deflection Factor = switch X Conversion
setting Factor
This Adjusted Deflection Factor
is correct if the VAR-
IABLE control has not been moved from the position set in
step
1.
Operating Instructions-7A15
6. Measure the vertical deflection in divisions and deter-
mine the amplitude
by the following formula:
Signal
Amplitude
Adjusted
Deflection X
Factor deflection
(divisions)
Example: Assume a reference signal amplitude
of 30
volts, a VOL TS/DIV switch setting of 5 V and a vertical
deflection
of four divisions. Substituting these values in the
Deflection Conversion Factor formula (step 2):
Deflection
Conversion
Factor
30 volts
4 (div) X 5 V 1.5
Then with a VOL TS/DIV switch setting of 2 V, the
Adjusted Deflection Factor (step
5) is:
Adjusted Deflection Factor = 2 V X 1.5
volts/division 3
To determine the amplitude of an applied signal which
produces a vertical deflection
of five divisions, use the Sig-
nal Amplitude formula (step 6):
Signal
Amplitude =3 V X 5 (div) = 15 volts
2-7

NOTES

7A1S
SECTION 3
CIRCUIT DESCRIPTION
Change information, if any, affecting this section will be found at the rear of this manual.
Introduction
This section of the manual contains a description of the
circuitry used in the 7A15 amplifier. The description begins
with a discussion
of the instrument using the block diagram
shown
in the diagrams section. Then each circuit is des-
cribed
in detail using the block diagram to show intercon-
nections between the circuits and relationship
of the front
panel controls to the individual stages.
Complete schematics
of each circuit are given in the
Diagrams section. Refer to these diagrams throughout the
following circuit description for electrical values and rela-
tionship.
BLOCK DIAGRAM DESCRIPTION
The following discussion is provided to aid in under-
standing the overall concept of the 7A15 before
the indi-
vidual circuits are discussed
in detail. Each block on the
Block Diagram, (in the Diagrams section) represents an indi-
vidual circuit within the instrument. The number on each
block refers
to the diagram on which the complete circuit is
found.
The signal
to be displayed on the CRT is applied to the
INPUT connector, through the input coupling circuit
to the
VOLTS/DIV switch. The VOLTS/DIV switch provides the
appropriate input attenuation and applies the signal to the
Input Amplifier
(0103A-0103B·0110-0210·0112·0212).
The gain setting, variable gain, and variable balance adjust-
ments are contained
in this stage. The input signal is
changed from single-€nded to differential by this stage and
applied
to the polarity selection stage. The Polarity Selec·
tion stage
(0130·0230-0140·0240) provides signal polarity
inversion when the
front panel POLAR ITY switch is set to
INVERT.
The
Output Amplifier stage (0160·0260·0170·0270)
provides vertical positioning of the CRT display and im·
pedance match
ing between the 7A15 and the oscilloscope
vertical input. The Trigger Pickoff circuit,
0180·0280-0185·0285, takes the signal from the emitters
of 0170·0270 and amplifies it to provide + and -trigger
signals for the time base unit.
®
In addition to the functions of the amplifier just ex·
plained, the 7A15 also provides readout logic for
the indio
cator oscilloscope. Logic is supplied which identifies the
display Polarity and the deflection factor, whether calibra·
ted or uncalibrated. When
the IDENTIFY button is pressed,
the readout is erased and the word IDENTIFY appears. At
the same time, the bottom of R274 is grounded to deflect
the trace upward approximately 0.25 division.
DETAILED CIRCUIT DESCRIPTION
Input Coupling
Input signals applied to the INPUT connector can be
AC·coupled, DC-coupled,
or internally disconnected. With
the coupling switch set to AC, the signal path is through
C1·R1·COUPLING switch-C3·R3 and through the VOL
TS/
DIV switch to the input amplifier. In this position, C1 pre·
vents the
DC component of the signal from passing to the
amplifier. With
the COUPLING switch set to DC, the signal
path
is through C3·R3 and the VOLTS/DIV switch to the
amplifier input. With
the COUPLING switch set to GND,
the input signal
is AC-coupled through C1·R 1·R2 to ground
to provide a constant load for the signal source. At the
same time, the amplifier input is grounded to provide a 0
volts reference level. Resistor
R2 allows C1 to be pre·
charged
in the GND position so the trace will remain on
screen when the
AC button is pressed with a high DC level
applied.
Input Attenuator
The effective overall deflection factor of the 7A15 is
determined by the VOLTS/DIV switch attenuators. The
basic deflection factor of the 7A15
is 5 mV per division of
deflection.
To increase this basic deflection factor to the
values indicated on the
front panel, precision attenuators
are switched into the input circuit. The input attenuators
form frequency·compensated voltage dividers. For
DC and
low·frequency signals, they 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. However, at higher frequencies, the reactance of
the capacitors decreases and the attenuator becomes pri-
marily a capacitance voltage divider.
In addition to providing constant attenuation at all fre·
quencies within the bandwidth of the system, the input
3·1

Circuit Description-7A15
attenuators are designed
to maintain the same input RC
characteristics for each setting of the VOLTS/DIV switch.
The attenuators contain adjustable shunt capacitors
to pro-
vide input capacitance.
Input Amplifier
The signal from the input attenuator is connected to the
Input Amplifier through
Rl09-Rl00-Rl0l-Cl0l. These
resistors are part
of the attenuation network at all VOL TS/
DIV switch positions. Resistor R101 limits the overdrive
gate current of input FET
0103A. Cl0l-CR102-Cl02 pro-
vide an input protection circuit
to protect 0103A from
large negative voltage swings. Protection from large positive
voltage swings
is provided by 0110, which effectivelY
clamps
the source of input FET 0103A to the +15 volt
supply.
The input signal
is coupled through source follower
0103A and emitter follower 0110 to the base of 0112,
one-half of the input paraphase amplifier. The other half of
the paraphase amplifier,
0212, is a grounded-base con-
figuration. The reference voltage level
at the base of 0212
is set by the V AR BAL control, a front panel adjust. The
paraphase amplifier converts the single-ended input into a
differential
output. The gain of the amplifier is set in this
stage by
front panel GA IN control R 121 with the variable
control set
to the CAL IN position. With the VARIABLE
control
in the outward (uncalibrated) position and turned
fully counterclockwise
to minimum resistance, the gain of
the amplifier
is reduced by a factor of at least 2.5. This
extends the maximum uncalibrated deflection factor
to at
least 12.5 volts/division. Damping resistors R114 and R214
in the collector circuits of 0112 and 0212 respectively,
serve
to damp out any ringing or oscillations. Cl14-Rl15
and C214-R215 are thermal compensation networks.
Polarity Selection Stage
The Polarity Selection Stage made up of
0130-0230-0140-0240 provides a means of inverting the
input signal. With the POLARITY switch set
to +UP, 0130
and 0230 are biased on and the signal is passed straight
through
to the output amplifier. With the POLAR ITY
switch set to INVERT, 0130 and 0230 are biased off and
0140-0240 are turned on to provide signal inversion.
C131-R131 and C231-R231 are thermal compensation net-
works.
Output Amplifier
The Output Amplifier is composed of
0160-0260-0170-0270 and their associated circuitry. The
vertical POSITION control
is located in the input to this
stage. Thermistor RT151 and varactors
CR 154-CR254 pro-
vide proper compensation for transient response with
changes of temperature. Thermal compensation for
0160
3-2
and 0260 is provided by R161-C161 and R261-C261
respectively. R171-C171 and R271-C271 provide thermal
compensation for 0170 and 0270 respectively.
C253-C175-R175 are high-frequency peaking adjustments
for calibration of the 7A15.
Trigger Pickoff Stage
The Trigger Pickoff stage consists of
Q 180-0280-0185-0285 and their associated circuitry.
Emitter followers
0180 and 0280 provide isolation be-
tween the trigger output circuit and the signal output cir-
cuit
to prevent loading of the signal output amplifier.
R186-C186 and R284-C284 provide thermal compensation
for
0185 and 0285 respectively. The trigger output ampli-
tude is approximately the same as the signal output ampli-
tude.
Readout Block
An analog coding system is used in the 7A15 to convey
information from the plug-in
to the oscilloscope readout
section. Each symbol used by the 7A15 requires two cur-
rents
to define it. This readout information is encoded on
two
output lines, interface connectors A37 and B37, by the
resistors between
output lines and interface connectors
A30, A32, A33, B29, B32 and
833.
Refer to Schematic Diagram 3 in the Diagrams section to
find the resistors associated with a particular setting of the
VOLTS/DIV switch.
The probe connected
to the INPUT connector forms a
voltage divider with R75
to the -15 volt power supply. The
amount of probe resistance will determine the bias applied
to the base of 080. For example, with a lOX attenuator
probe such
as the P6053 Probe connected to the INPUT
connector, the bias applied
to the base of 080 will allow
100 microamperes of collector current
to flow. When the
time slot pulse from the oscilloscope interrogates interface
connector
833, this 100 microamperes of current is added
to the current corresponding to the setting of the VOL TS/
DIV switch to increase the deflection factor (in the dis-
played readout) by a factor of 10. Refer
to the appropriate
oscilloscope Instruction Manual for more information on
the Readout System.
The oscilloscope displayed readout will
give the correct
deflection factor from the probe tip (using the recom-
mended attenuator probes), whereas the VOLTS/DIV knob
on the plug-in will display only the plug-in deflection fac-
tor.
The trace IDENTIFY
button, when pressed, does two
things:
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

1. It grounds the junction of R75-R274 (bottom end
of R274) to deflect the trace upward about 0.25 divi-
sion.
2. The base of
080, which is connected to the junc-
tion
of R75-R274, is also grounded. This turns 080 on
Circuit
Description-7A15
hard, and the displayed readout is replaced by the word
IDENTIFY.
These
two actions aid in identifying the 7A15 trace
when multiple traces are displayed on the CRT. When
the
IDENTIFY button is released, the readout is restored to its
previous display.
3-3

NOTES

7A15
SECTION 4
MAINTENANCE
Change information, if any, affecting this section will be found at the rear of this manual.
Introduction
This section of the manual contains maintenance infor-
mation for use
in preventive maintenance, corrective main-
tenance and troubleshooting of the 7A15.
PREVENTIVE MAINTENANCE
General
Preventive maintenance consists of cleaning, visual in-
spection, lubrication, etc. Preventive maintenance per-
formed on a regular basis may prevent instrument break-
down, and will improve reliability
of this instrument. The
severity of
the environment to which the 7A15 is subjected
determines
the frequency of maintenance. A convenient
time to perform preventive maintenance is preceding recali-
bration of the instrument.
Cleaning
The 7A15 shou Id be cleaned as often as operating cond i-
tions require. Accumulation of dirt in the instrument can
cause overheating and
component breakdown. Dirt on the
components acts as an insulating blanket and prevents
effective heat dissipation. It may also provide an electrical
conduction
path.
Avoid the use of chemical cleaning agents which
might damage the plastics used in this instrument. Do
not apply any solvent containing ketones, esters or
halogenated hydrocarbons. To clean, use only water
soluble detergents, ethyl, methyl or isopropyl
alcohol.
The covers of the oscilloscope minimize the amount of
dust which reaches the interior of the 7A15. Operation of
the system without the oscilloscope covers in place necessi-
tates more frequent cleaning. When the 7A15 is not in use,
it should be stored
in a protected location, such as a dust-
tight cabinet.
Exterior. Loose
dust accumulated on the outside of the
7A15 can be removed with a soft cloth or small paint
brush. The paint brush is particularly useful for dislodging
dirt on and around the front-panel controls. Dirt which
remains can be removed with a soft cloth dampened in a
mild detergent and water soluton. Abrasive cleaners should
not be used.
Interior. Dust
in the interior of the instrument should
be removed occasionally
due to its electrical conductivity
under high-humidity conditions. The best way to clean the
interior is to blow off the accumulated dust with dry, low-
velocity air. Remove any
dirt which remains with a soft
paint brush or a cloth dampened with a mild detergent and
water solution. A cotton-tipped applicator
is useful for
cleaning
in narrow spaces.
Visual Inspection
The 7A15 should be inspected occasionally for such
defects
as broken connections, broken or damaged circuit
boards, improperly seated transistors and heat-damaged
parts.
The corrective procedure for most visible defects
is ob-
vious. However, particular care must be taken
if heat-
damaged
components are found. Overheating usually indi-
cates
other trouble in the instrument; therefore, it is
important that the cause of overheating be corrected to
prevent a recurrence of the damage.
Semiconductor checks
Periodic checks of the semiconductors in the 7A15 are
not recommended. The best check of a semiconductor's
performance
is its actual operation in the instrument. More
details on checking semiconductor operation are given
under Troubleshooting.
Recalibration
To ensure accurate measurements, check the calibration
of this instrument after each 1000 hours of operation, or
every six
months if used infrequently. In addition, replace-
ment of components may necessitate recalibration of the
affected circuits. Complete cal ibration instructions are
given
in Section 5.
4-'

Maintenance-7 A15
Composition Resistors:
Ceramic Capacitors:
00 and 0 -1 st, 2nd and 3rd significant figures;
® -multiplier; CD -tolerance;
Resistor and Capacitor Color Code
Signifi- I Multiplier I Tolerance
.cant I
Resis- ICapaci-j Resis- Capaci-
Color Figures
~~ tors tors tors
Silver I 10.2 I
+10%
Gold I 10-
1
+5%
Black I, _~0 __ ~_~1 __ -+~~-+ __ ~~_~_+~2~0~~_o_o_r_1
-!_ 2pF*
Brown I 10 10 + 1% + 1% or
Red
I 2
10
2
Orange I 3
Yellow 1 4
Green 1 5 105
Blue
I 6 106
Violet I 7
Gray I 8
White 1 9
(none) I
0.1 pF*
10
2
+2% I
+2%
10
3 I
+3% I +3%
--+--_1_04---i1_~4 % .:1 __ +_-::-1 ~::-:-~,-=-:_o _
105 +0.5% +5% or
0.5
pF*
10
6
10-
2
10-
1
+20%
+80%
-20%
or 0.25 pF*
+10% or
1 pF*
+10% or
1
pF*
*For capacitance of 10 pF or less.
@ -temperature coefficient.
NOTE: (!) and/or @ color code for capacitors depends upon
manufacturer
and capacitor type. May not be present In some cases.
Fig.
4·1. Color code for resistors and ceramic capacitors.
The Performance Check/Calibration procedure can also
be helpful
in localizing certain troubles in the instrument.
In some cases, minor troubles may be revealed and/or cor-
rected by calibration.
TROUBLESHOOTING
Introduction
The following information is provided to facilitate
troubleshooting of the 7A15. Information contained
in
other sections of this manual should be used along with the
following information
to aid in locating the defective com-
ponent. An understanding of the circuit operation
is very
helpful
in locating troubles. See the Circuit Description sec·
tion for complete information.
Troubleshooting Aids
Diagrams. Circuit diagrams are given on foldout pages in
the Diagrams Section. The component number and electri-
cal value of each component
in this instrument are shown
on the diagrams. Important voltages and waveforms are also
shown on the diagrams.
4-2
Resistor Color Code. In addition to the brown composi-
tion resistors, some metal-film resistors are used
in this
instrument. The resistance values of composition resistors
and metal·film resistors are color-coded on
the components
some metal-film resistors may have the value printed on the
body) with EIA color code.
The color code is read starting
with the stripe nearest the end
of the resistor. Composition
resistors have four stripes which consist of
two significant
figures, a multiplier and a tolerance value (see Fig. 4-1).
Metal-film resistors have five stripes consisting
of three sig-
nificant figures, a multiplier and a tolerance value.
Capacitor Marking. The capacitance value of a common
disc capacitor
or small electrolytic is marked in microfarads
on the side of the component body. The white ceramic
capacitors used
in the 7A15 are color coded in picofarads
using a modified EIA code (see Fig. 4·1).
Diode Color Code. The cathode end of each glass-
encased diode
is indicated by a stripe, a series of stripes or a
dot. For most silicon or germanium diodes with a series of
stripes, the color code also indicates the type of diode or
identifies
the Tektronix Part Number, using the resistor
color code system (e.g., a diode color coded blue or pink-
®