Tektronix 7B80 User manual

l^ronix
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7B80
TIME BASE
WITH OPTIONS
Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon
INSTRUCTION MANUAL
97077 Serial Number 'Td nil 9
070-1959-00 First Printing DEC 1975
Revised MAR 1981

Copyright ®1975 Tektronix, Inc. All rights reserved.
Contents of this publication may not be reproduced in
any form without the written permission of Tektronix, Inc.
Products of Tektronix, Inc. and its subsidiaries are
covered by U.S. and foreign patents and/or pending
patents.
TEKTRONIX, TEK, SCOPE-MOBILE, and are
registered trademarks of Tektronix, Inc. TELEQUIP-
MENT is aregistered trademark of Tektronix U.K
Limited.
Printed in U.S.A. Specification and price change
privileges are reserved.

7B80 Instruction
TABLE OF CONTENTS
PAGE
LIST OF ILLUSTRATIONS iii
LIST OF TABLES iv
SAFETY SUMMARY v
SECTION 1OPERATING INSTRUCTIONS
INSTALLATION 1-1
CONTROLS, CONNECTORS,
AND INDICATORS 1-1
FUNCTIONAL CHECK 1-1
Setup Procedure 1-1
Sweep Functions 1-4
Triggering Functions 1-4
GENERAL OPERATING INFORMATION ..1-5
Triggering Switch Logic 1-5
Triggering Modes 1-5
Trigger Coupling 1-6
Trigger Source 1-6
PAGE
Trigger Slope 1-7
Trigger Level 1-7
Horizontal Sweep Rates 1-7
Time Measurement 1-7
Sweep Magnification 1-7
Variable Hold Off 1-7
Mainframe Operating Modes T9
APPLICATIONS 1-10
TIME-INTERVAL MEASUREMENTS 1-10
Period and Frequency Measurements 1-10
Rise-Time and Fall-Time Measurements. ..1-11
Pulse Width Measurements 1-12
DELAYED-SWEEP MEASUREMENTS 1-12
X-Y PHASE MEASUREMENTS 1-12
SECTION 2SPECIFICATION
STANDARD ACCESSORIES 2-3
WARNING
THE REMAINING SECTIONS OF THIS MANUAL CONTAIN SER-
VICING INSTRUCTIONS. THESE SERVICING INSTRUCTIONS
ARE FOR USE BY QUALIFIED PERSONNEL ONLY. TO AVOID
ELECTRICAL SHOCK, DO NOT PERFORM ANY SERVICING
OTHER THAN THAT CALLED OUT IN THE OPERATING IN-
STRUCTIONS UNLESS QUALIFIED TO DO SO.

7B80 Instruction
TABLE OF CONTENTS (CONT.)
PAGE
SECTIONS THEORY OF OPERATION
BLOCK DIAGRAM DESCRIPTION 3-1
DETAILED CIRCUIT DESCRIPTION 3-1
LOGIC FUNDAMENTALS 3-1
NON-DIGITAL DEVICES 3-2
FRONT-PANEL DISTRIBUTION .... 3-7
TRIGGER GENERATOR
LOGIC 3-9
SWEEP GENERATOR <s>
TIME/DIVISION READOUT <^. 3-14
INTERFACE CONNECTORS AND
POWER SUPPLY ^3-14
SECTION 4MAINTENANCE
PREVENTIVE MAINTENANCE 4-1
CLEANING 4-1
VISUAL INSPECTION 4-1
LUBRICATION 4-1
SEMICONDUCTOR CHECKS 4-2
ADJUSTMENT AFTER REPAIR 4-2
TROUBLESHOOTING 4-3
TROUBLESHOOTING AIDS 4-3
TROUBLESHOOTING EQUIPMENT 4-5
TROUBLESHOOTING TECHNIQUES 4-6
CORRECTIVE MAINTENANCE 4-9
OBTAINING REPLACEMENT PARTS 4-9
PAGE
SOLDERING TECHNIQUES 4-9
COMPONENT REMOVAL AND
REPLACEMENT 4-10
Circuit Boards 4-10
Switches 4-12
Semiconductors 4-12
Interconnecting Pins 4-13
Front-Panel Lights 4-16
ADJUSTMENT AFTER REPAIR 4-16
INSTRUMENT REPACKAGING 4-16
SECTIONS PERFORMANCE CHECK AND
ADJUSTMENT
PRELIMINARY INFORMATION 5-1
TEST EQUIPMENT REQUIRED 5-1
INDEX TO PERFORMANCE CHECK
AND ADJUSTMENT PROCEDURE 5-3
PRELIMINARY PROCEDURE 5-3
SECTION 6REPLACEABLE ELECTRICAL PARTS
SECTION 7INSTRUMENT OPTIONS
SECTIONS DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
SECTION 9REPLACEABLE MECHANICAL PARTS
CHANGE INFORMATION

7B80 Instruction
LIST OF ILLUSTRATIONS
FIGURE
NO. PAGE
Frontispiece vi
1-1 Location of release latch 1-1
1-2 Front-panel controls, connectors,
and indicators 1-2
1-3 Effect of LEVEL control and SLOPE
switch on crt display 1-8
1-4 Area of graticule used for most accurate
time measurements 1-9
1-5 Operation of sweep magnifier 1-9
1-6 Measuring the period and determining
the frequency of adisplayed waveform ...1-10
1-7 Measuring the rise time and fall time of
adisplayed waveform 1-11
1-
8Measuring the pulse width of adisplayed
waveform 1-12
2-
17B80 dimensional drawing 2-3
3-
1Basic block diagram of the 7B80
Time-Base Unit 3-2
3-2 Detailed block diagram of Trigger
Generator 3-6
3-3 Functional diagram of Trigger Source
Selector 3-8
3-4 Timing diagram for Gate Generator
(Q92, Q96, Q98) 3-9
3-5 Detailed block diagram of Logic circuit ...3-10
3-
6Detailed block diagram of Sweep
Generator 3-12
4-
1Lubrication procedure for atypical
cam switch 4-2
4-2 Semiconductor lead configuration 4-4
4-3 Inter-board multi-pin connector
assembly 4-5
4-4 End-lead multi-pin connector
assembly 4-5
FIGURE
NO. PAGE
4-5 Location of pin numbers on Interface
connector 4-5
4-6 7B80 troubleshooting chart 4-8
4-7 Readout board removal procedure 4-11
4-8 Coaxial end-lead connector assembly 4-12
4-9 Cam switch removal procedure 4-14
4-10 Removal procedure for typical
push-button switch 4-15
4-1 1Exploded view of circuit-board pin
and ferrule 4-16
4-12 Front-panel light socket assembly 4-16
The illustrations in Section 8are located near their associat-
ed Diagrams on the foldout pages.
8-1 Semiconductor lead configurations.
8-2 Location of circuit boards in the 7B80.
8-3 A1—Interface circuit board assembly.
8-4 A2—Trigger circuit board assembly.
8-5 A3—Readout circuit board assembly.
8-6 A1 —Interface circuit board assembly.
8-7 A2—Trigger circuit board assembly.
8-8 A1 —Interface circuit board assembly.
8-9 A1 —Interface circuit board assembly.
8-10 A3—Readout circuit board assembly.
8-1 1A1—Interface circuit board assembly.
8-12 A3—Readout circuit board assembly.
8-13 A1 —Interface circuit board assembly.
8-14 A5—X-Y Switch circuit board assembly.
8-15 Location of Sweep Timing adjustments.
8-16 Location of Triggering adjustments.

7B80 Instruction
LIST OF TABLES
TABLE
NO. page
2-1 Electrical Characteristics 2-1
2-2 Environmental Characteristics 2-3
2-
3Physical Characteristics 2-3
3-
1Basic Logic Reference 3-3
TABLE
NO. page
3-2 Readout Character Selection 3-15
5-1 Test Equipment 5-2
5-2 Sweep Timing .5-10
5-3 Magnified Sweep Timing 5-1
1
@
IV

7B80 Instruction
SAFETY SUMMARY
This manual contains safety information which the user must follow to ensure safe operation of this instrument. WARNING
information is intended to protect the operator; CAUTION information is intended to protect the instrument. The following
are general safety precautions that must be observed during all phases of operation and maintenance.
WARNING
Ground the Instrument
To reduce electrical-shock hazard, the mainframe (oscilloscope) chassis must be properly grounded. Refer to the mainframe
manual for grounding information.
Do Not Operate in Explosive Atmosphere
Do not operate this instrument in an area where flammable gases or fumes are present. Such operation could cause an
explosion.
Avoid Live Circuits
Electrical-shock hazards are present in this instrument. The protective instrument covers must not be removed by operating
personnel. Component replacement and internal adjustments must be referred to qualified service personnel.
Do Not Service or Adjust Alone
Do not service or make interna! adjustments to this instrument unless another person, capable of giving first aid and resusci-
tation, is present.
WARNING i
Warning Statements
Warning statements accompany potentially dangerous procedures in this manual. The following warnings appear in this
manual and are listed here for additional emphasis.
To avoid electrical shock, disconnect the instrument from the power source before soldering.
To avoid electrical shock, disconnect the instrument from the power source before replacing components.
Handle silicone grease with care. Avoid getting silicone grease in eyes. Wash hands thoroughly after use.

7B80 Instruction
TRIGGERING
LEVEL
HOLD
OFF
RESIT
MAG
X10 VABtABtE fCAt W|
TIME/OIV
OUTi-tO
£XT TRIG IN
TEKTflOKIX^ IMS
TIME BASE
7B80
7B80 Features
The 7B80 Time-Base unit provides calibrated sweep rates from 5seconds to 10 nanoseconds and triggering to 400 megahertz
for 7700-, 7800-, and 7900-series oscilloscopes. AX10 Magnifier increases each sweep rate by afactor of 10 and aVARI-
ABLE TIME/DIV control provides continuously variable sweep rates between calibrated steps. Variable hold off and alpha-
numeric readout are provided. Also, when operating in the AUTO TRIGGERING MODE, abright baseline trace is displayed
in the absence of atrigger signal. The 7B80 can be operated as an independent time base or asadelayed-sweep unit with acom-
panion delaying time-base unit.
1958-1
@
VI

Section 1—7B80
OPERATING INSTRUCTIONS
The 7B80 Time-Base unit operates with aTektronix 7700-, 7800-, and 7900-series oscilloscope mainframes and a7A-series
amplifier unit to form acomplete oscilloscope system. This section describes the operation of the front-panel controls and
connectors, provides general operating information, afunctional check procedure, and basic applications for this instrument.
INSTALLATION
The time-base unit is designed to operate in the horizontal
plug-in compartment of the mainframe. This instrument
can also be installed in avertical plug-in compartment to
provide avertical sweep on the crt. However, when used in
this manner, there are no internal triggering or retrace
blanking provisions, and the unit may not meet the specifi-
cations given in Section 2.
To install the unit in aplug-in compartment, push it in until
it fits firmly into the compartment. The front panel of the
unit should be flush with the front panel of the mainframe.
Even though the gain of the mainframe is standardized, the
sweep calibration of the unit should be checked when in-
stalled. The procedure for checking the unit is given under
Sweep Functions in the Functional Check procedure in this
section.
To remove the unit, pull the release latch (see Figure 1-1
)
to disengage the unit from the mainframe, and pull it out of
the plug-in compartment.
CONTROLS, CONNECTORS, AND INDICATORS
All controls, connectors, and indicators required for the
operation of the time-base unit are located on the front
panel. Figure 1-2 shows and provides abrief description of
all front-panel controls, connectors, and indicators. More
detailed information is given in the General Operating
Instructions.
FUNCTIONAL CHECK
The following procedures are provided for checking basic
instrument functions. Refer to the description of the con-
trols, connectors, and indicators while performing this pro-
cedure. If performing the functional check procedure
reveals amalfunction or possible improper adjustment, first
check the operation of the associated plug-in units, then re-
fer to the instruction manual for maintenance and adjust-
ment procedures.
Setup Procedure
1
.
Install the time-base unit being checked in the Ahori-
zontal compartment of the mainframe.
2.
Install an amplifier plug-in unit in avertical compart-
ment.
3.
Set the time-base unit controls as follows:
SLOPE (+)
MODE P-P AUTO
COUPLING AC
SOURCE INT
POSITION Midrange
TIME/DIV 1ms
VARIABLE Calibrated (Pushed in
(CAL IN)
HOLD OFF MIN (fully counter-
MAG clockwise)
XI (pushed in)
4.
Turn on the mainframe and allow at least 20 minutes
warmup.
Fig. 1-1. Location of release latch.

Operating instructions—7B80
OC2X3Y4)mC7
«a.®(sa \TRIG DTRIGGERING
LEVEL \III
MODE COUPUmC SOURCE
PPAUTO AC INT
\rCl i<p»..
AUTO ACLFREJ LINE
NORM ACHfREJ EXT
ySINGLE SWP V-
/'-N. IFINE \ff'^ fnl
(Q1LPOSITION \“li=!l OFF •j
^—RESET
I
/Vui mag ll /if)
in X
1
MIN 1vy
OUT xio VARIABLEICAL IN} I
7B80
—nl-
OUT^IO 1I1I
EXT TRIG IN
IIMn
TIME BASE
TRIGGERING
EXTERNAL
TRIGGER
INPUT
Fig. 1-2. Front-panel controls, connectors, and indicators.

©©©©©©©
©©©©©©
©
©©
Operating Instructions—7B80
TRIGGERING
LEVEL Control—Selects apoint on the trigger signal where triggering occurs.
SLOPE Switch—Permits sweep to be triggered on negative or positive-going portions of the trigger signal.
READY Indicator— Illuminates when sweep circuit is armed (SINGLE SWEEP Mode).
TRIG'D Indicator— Illuminates when the display is triggered.
MODE Pushbuttons—Selects the operating mode of the triggering circuit.
COUPLING Pushbuttons—Selects the method of coupling the trigger signal to triggering circuit.
SOURCE Pushbuttons—Selects source of the trigger signal.
SWEEP
POSITION Control—Provides horizontal positioning.
FINE Control—Provides precise horizontal positioning.
MAG Pushbutton—Selects magnified X10 or unmagnified sweep.
HOLD OFF Control-Permits hold off period to be varied to improve trigger stability on repetitive complex waveforms.
TIME/DIV Selector—Selects the sweep rate of the sweep generator.
VARIABLE Control and CAL Switch-Selects calibrated or uncalibrated sweep rates. Uncalibrated sweep rates can
be continuously reduced to at least the sweep rate of the next slower position.
SWP CAL Adjustment-Compensates for basic timing changes due to the differences in sensitivity of mainframes
EXTERNAL TRIGGER INPUT
EXT TRIG ATTENUATOR—Selects attenuation factor for external trigger signals.
EXT TRIG IN Connector—Connector (BNC type) provides input for external trigger signals.
1958-4
Fig. 1-2. Front-panel controls, connectors, and indicators (cont.).

Operating Instructions—7B80
5.
Set the mainframe vertical and horizontal modes to dis-
play the plug-in units used and adjust the intensity and
focus for awell-defined display. See the oscilloscope main-
frame and amplifier unit instruction manuals for detailed
operating instructions.
Sweep Functions
NORMAL SWEEP. Perform the following procedure to ob-
tain anormal sweep and to demonstrate the function of the
related controls:
1.
Perform the preceding Setup Procedure.
2.
Connect a0.4-volt, 1-kilohertz signal from the main-
frame calibrator to the amplifier unit input.
3.
Set the amplifier unit deflection factor for 4divisions of
display.
4.
Adjust the LEVEL control for astable display.
5.
Turn the POSITION control and note that the trace
moves horizontally.
6.
Turn the FINE control and note that the display can be
precisely positioned horizontally.
7.
Check the display for one complete cycle per division. If
necessary, adjust the front-panel SWP CAL screwdriver ad-
justment for one complete cycle per division over the
center 8graticule divisions. Be sure that the timing of the
mainframe calibrator signal is accurate to within 0.25%
(+20 to +30° C).
8.
Press to release the VARIABLE (CAL IN) control. Turn
the VARIABLE (CAL IN) control fully counterclockwise
and note that the displayed sweep rate changes to at least
the next slower TIME/DIV switch setting (i.e., 2milli-
seconds/division). Press the VARIABLE (CAL IN) knob in
to the calibrated position.
MAGNIFIED SWEEP. Perform the following procedure to
obtain aX10 magnified display and to demonstrate the
function of the related controls:
1
.
Obtain aone cycle per division display as described in
the preceding Normal Sweep procedure.
2. Press to release the MAG button (X10). Note that the
unmagnified display within the center division of the grati-
cule is magnified to about 10 divisions.
3. Press the MAG button (XI).
Triggering Functions
Perform the following procedure to obtain atriggered
sweep and to demonstrate the functions of the related
controls:
1.Obtain adisplay as described in the preceding Normal
Sweep procedure.
2. Press the AUTO MODE button and turn the LEVEL
control fully counterclockwise to obtain afree-running
sweep.
3.
Slowly turn the HOLD OFF control clockwise and note
that astable display can be obtained at several positions of
the HOLD OFF control. Return the HOLD OFF control to
the fully counterclockwise (MIN) position.
NOTE
The HOLD OFF control varies the sweep hold-off
time which effectively changes the repetition-rate
of the horizontal sweep signal. However, its pri-
mary function is to obtain a stable display of
complex waveforms which are otherwise difficult
to trigger.
4.
Press the AC, AC HF REJ, and DC COUPLING buttons
for both the +and —positions of the SLOPE switch and
check for astable display (LEVEL control may be adjusted,
if necessary, to obtain astable display).
5.
Apply the 0.4-volt, 1kilohertz signal from the main-
frame calibrator to the amplifier unit and to the EXT TRIG
IN connector.
6. Press the EXT SOURCE button and set the amplifier
unit deflection factor for a4-division display.
7. Press the AC, AC HF REJ, and DC COUPLING buttons
for both the +and —positions of the SLOPE switch and
check for astable display (LEVEL control may be adjusted,
if necessary, for astable display).

Operating Instructions—7B80
8. Press the AC COUPLING, INT SOURCE, and NORM
MODE buttons. Adjust the LEVEL control for astable
display.
9. Press the AUTO MODE button and adjust the LEVEL
control for afree-running display.
10. Press the NORM MODE button and check for no
display.
11. Adjust the LEVEL control for astable display and
press the SINGLE SWP MODE button.
12. Note that one trace occurs when the RESET MODE
button is pressed.
13, Disconnect the mainframe calibrator signal from the
amplifier unit input and press the RESET MODE button.
Check for no display and note that the READY indicator
is lit.
14. Note that one trace occurs and that the READY indi-
cator extinguishes when the mainframe calibrator signal is
reconnected to the amplifier unit input.
GENERAL OPERATING INFORMATION
Triggering Switch Logic
The MODE, COUPLING, and SOURCE push buttons of the
TRIGGERING switches are arranged in asequence which
places the most-often used position at the top of each series
of push buttons. With this arrangement, astable display can
usually be obtained by pressing the top push buttons; P-P
AUTO, AC, INT. When an adequate trigger signal is applied
and the LEVEL control is correctly set, the unit is triggered
as indicated by the illuminated TRIG'D light. If the
TRIC'D light is not on, the LEVEL control is either at a
setting outside the range of the trigger signal applied to this
unit from the vertical unit, the trigger signal amplitude is in-
adequate, or its frequency is below the lower frequency
limit of the AC COUPLING switch position. If the desired
display is not obtained with these buttons pushed in, other
selections must be made. Refer to the following discussions
or the instruction manuals for the associated oscilloscope
mainframe and vertical unit(s) for more information.
Triggering Modes
The MODE push-button switches select the mode in which
the sweep is triggered.
P-P AUTO. The P-P AUTO MODE provides atriggered dis-
play at any setting of the LEVEL control whenever an ade-
quate trigger signal is applied. The range of the LEVEL
control in the P-P AUTO MODE is between approximately
10% and 90% of the peak-to-peak amplitude of the trigger
signal. The LEVEL control can be set so that the displayed
waveform starts at any point within this range on either
slope. The trigger circuits automatically compensate for a
change in trigger-signal amplitude. Therefore, if the LEVEL
control is set to start the waveform display at acertain per-
centage point on the leading edge of alow-amplitude signal,
it triggers at the same percentage point on the leading edge
of ahigh-amplitude signal if the LEVEL control is not
changed. When the trigger repetition rate is outside the
parameter given in the Specification section, or when the
trigger signal is inadequate, the sweep free runs at the rate
indicated by the TIME/DIV switch to produce abright
base-line reference trace (TRIG'D light off). When an ade-
quate trigger signal is again applied, the free-running condi-
tion ends and atriggered display is presented.
The P-P AUTO MODE is particularly useful when observing
aseries of waveforms, since it is not necessary to reset the
LEVEL control for each observation. The P-P AUTO
MODE is used for most applications because of the ease of
obtaining atriggered display. The AUTO, NORM, and
SINGLE-SWP MODE settings may be used for special
applications.
AUTO. The AUTO MODE provides atriggered display
with the correct setting of the LEVEL control whenever an
adequate trigger signal is applied (see Trigger Level discus-
sions). The TRIG'D light indicates when the display is
triggered.
When the trigger repetition rate is outside the frequency
range selected by the COUPLING switch or the trigger sig-
nal is inadequate, the sweep free runs at the rate indicated
by the TIME/DIV switch (TRIG'D indicator off). An ade-
quate trigger signal ends the free-running condition and a
triggered display is presented. The sweep also free runs at
the rate indicated by the TIME/DIV switch when the
LEVEL control is at asetting outside the amplitude range
of the trigger signal. This type of free-running display is
useful when it is desired to measure only the peak-to-peak
amplitude of asignal without observing the waveshape
(such as bandwidth measurements).
NORMAL. The NORM MODE provides atriggered display
with the correct setting of the LEVEL control whenever an
adequate trigger signal is applied. The TRIG'D light indi-
cates when the display is triggered.
@1-5

Operating Instructions—7B80
The normal trigger mode must be used to produce triggered
displays with trigger repetition rates below about 30 hertz.
When the TRIC'D light is off, no trace is displayed.
SINGLE SWEEP. When the signal to be displayed is not re-
petitive or varies in amplitude, waveshape, or repetition
rate, aconventional repetitive type display may produce an
unstable presentation. Under these circumstances, astable
display can often be obtained by using the single-sweep
feature of this unit. The single-sweep mode is also useful to
photograph non-repetitive or unstable displays.
To obtain asingle-sweep display of arepetitive signal, first
obtain the best possible display in the NORM MODE. Then,
without changing the other TRIGGERING controls, press
the SINGLE SWP RESET button. Asingle trace is present-
ed each time this button is pressed. Further sweeps cannot
be presented until the SINGLE SWP RESET button is pres-
sed again. If the displayed signal is acomplex waveform
composed of varying amplitude pulses, successive single-
sweep displays may not start at the same point on the wave-
form. To avoid confusion due to the crt persistence, allow
the display to disappear before pressing the SINGLE SWP
RESET button again. At fast sweep rates, it may be diffi-
cult to view the single-sweep display. The apparent trace
intensity can be increased by reducing the ambient light
level or by using aviewing hood as recommended in the
mainframe instruction manual.
When using the single-sweep mode to photograph wave-
forms, the graticule may have to be photographed
separately in the normal manner to prevent over exposing
the film. Be sure the camera system is well protected
against stray light, or operate the system in adarkened
room. For repetitive waveforms, press the SINGLE SWP
RESET button only once for each waveform unless the sig-
nal is completely symmetrical. Otherwise, multiple wave-
forms may appear on the film. For random signals, the lens
can be left open until the signal triggers the unit. Further
information on photographic techniques is given in the
appropriate camera instruction manual.
Trigger Coupling
The TRIGGERING COUPLING push buttons select the
method in which the trigger signal is connected to the trig-
ger circuits. Each position permits selection or rejection of
some frequency components of the signal which triggers
the sweep.
AC. AC COUPLING blocks the dc component of the trig-
ger signal. Signals with low-frequency components below
about 30 hertz are attenuated. In general, AC COUPLING
can be used for most applications. However, if the signal
contains unwanted frequency components or if the sweep is
to be triggered at alow repetition rate or dc level, one of
the other COUPLING switch positions will provide abetter
display.
AC LF REJ. AC LF REJ COUPLING rejects dc, and atten-
uates low-frequency trigger signals below about 30 kilo-
hertz. Therefore, the sweep is triggered only by the higher-
frequency components of the trigger signal. This position is
particularly useful for providing stable triggering if the trig-
ger signal contains line-frequency components. Also, the
AC LF REJ position provides the best alternate-mode verti-
cal displays at fast sweep rates when comparing two or
more unrelated signals.
AC HF REJ. AC HF REJ COUPLING passes all low-
frequency signals between about 30 hertz and 50 kilohertz.
Dc is rejected and signals outside the above range are atten-
uated. When triggering from complex waveforms, this posi-
tion is useful to provide astable display of the low-
frequency components.
DC. DC COUPLING can be used to provide stable trigger-
ing from low-frequency signals which would be attenuated
in the other COUPLING switch positions. DC COUPLING
can be used to trigger the sweep when the trigger signal
reaches adc level set by the LEVEL control. When using
internal triggering, the setting of the vertical unit position
control affects the triggering point.
Trigger Source
The TRIGGERING SOURCE push buttons select the
source of the trigger signal which is connected to the trigger
circuits.
INTERNAL. The INT position connects the trigger signal
from the vertical plug-in unit. Further selection of the in-
ternal trigger signal may be provided by the vertical plug-in
unit or by the mainframe; see the instruction manuals for
these instruments for more information. For most applica-
tions, the internal source can be used. However, some
applications require special triggering which cannot be ob-
tained in the INT position. In such cases, the LINE or EXT
positions of the SOURCE switches must be used.
LINE. The LINE position connects asample of the power-
line voltage from the mainframe to the trigger circuit. Line
triggering is useful when the input signal is time-related
{multiple or submultiple) to the line frequency. It is also
useful for providing astable display of aline-frequency
component in acomplex waveform.

Operating Instructions—7B80
EXTERNAL. The EXT position connects the signal from
the EXT TRIG IN connector to the trigger circuit. The ex-
ternal signal must be time-related to the displayed wave-
form for astable display. An external trigger signal can be
used to provide atriggered display when the internal signal
is either too low in amplitude for correct triggering or con-
tains signal components on which triggering is not desired.
It is also useful when signal tracing in amplifiers, phase-shift
networks, wave-shaping circuits, etc. The signal from a
single point in the circuit can be connected to the EXT
TRIG IN connector through aprobe or cable. The sweep is
then triggered by the same signal at all times and allows am-
plitude, time relationship, or waveshape changes of signals
at various points in the circuit to be examined without re-
setting the TRIGGERING controls.
The -hlO push button attenuates the external trigger signal
by afactor of 10. Attenuation of high amplitude external
trigger signals is desirable to increase the effective range of
the LEVEL control.
Trigger Slope
The TRIGGERING SLOPE switch (concentric with the
TRIGGERING LEVEL control) determines whether the
trigger circuit responds on the positive- or negative-going
portion of the trigger signal. When the SLOPE switch is in
the (+) (positive-going) position, the display starts on the
positive-going portion of the waveform (see Figure 1-3).
When several cycles of asignal appear in the display, the
setting of the SLOPE switch is often unimportant. How-
ever, if only acertain portion of acycle is to be displayed,
correct setting of the SLOPE switch is important to provide
adisplay that starts on the desired slope of the input signal.
Trigger Level
The TRIGGERING LEVEL control determines the voltage
level on the trigger signal at which the sweep is triggered.
When the LEVEL control is set in the +region, the trigger
circuit responds at amore positive point on the trigger sig-
nal. When the LEVEL control is set in the —region, the
trigger circuit responds at amore negative point on the
trigger signal. Figure 1-3 illustrates this effect with different
settings of the SLOPE switch.
To set the LEVEL control, first select the TRIGGERING
MODE, COUPLING, SOURCE, and SLOPE. Then set the
LEVEL control fully counterclockwise and rotate it clock-
wise until the display starts at the desired point.
Horizontal Sweep Rates
The TIME/DIV switch provides calibrated sweep rates from
5seconds/division to 10 nanoseconds/division in a1-2-5
sequence. The VARIABLE TIME/DIV control must be in
the calibrated position and the MAG switch set to XI to
obtain the sweep rate indicated by the TIME/DIV switch.
However, the mainframe crt readout will display the apprO'
priate sweep rate.
The VARIABLE TIME/DIV control includes atwo-position
switch to determine if the sweep rate is calibrated, or un-
calibrated. When the VARIABLE control is pressed in, it is
inoperative and the sweep rate is calibrated. When pressed
and released outward, the VARIABLE control is activated
for uncalibrated sweep rates, to at least the sweep rate of
the next slower position.
Acalibrated sweep rate can be obtained in any position of
the VARIABLE control by pressing in the VARIABLE con
trol. This feature is particularly useful when aspecific un-
calibrated sweep rate has been obtained and it is desired to
switch between calibrated and uncalibrated displays.
Time Measurement
When making time measurements from the graticule, the
area between the second and tenth vertical lines of the gra-
ticule provides the most linear time measurements (see
Figure 1-4). Position the start of the timing area to the
second vertical line and adjust the TIME/DIV switch so the
end of the timing area falls between the second and tenth
vertical lines.
Sweep Magnification
The sweep magnifier can be used to expand the display by a
factor of 10. The center division of the unmagnified display
is the portion visible on the crt in the magnified form (see
Figure 1-5). The equivalent length of the magnified sweep is
more than 100 divisions; any 10 division portion can be
viewed by adjusting the POSITION and FINE POSITION
controls to bring the desired portion into the viewing area.
When the MAG switch is set to X10 (OUT) the equivalent
magnified sweep rate can be determined by dividing the
TIME/DIV setting by 10; the equivalent magnified sweep
rate is displayed on the crt readout.
Variable Hold Off
The HOLD OFF control improves triggering stability on re-
petitive complex waveforms by effectively changing the
repetition rate of the horizontal sweep signal. The HOLD
OFF control should normally be set to its minimum setting.
When astable display cannot be obtained with the TRIG-
GERING LEVEL control, the HOLD OFF control can be
varied for an improved display. If astable display cannot be
obtained at any setting of the LEVEL and HOLD OFF con-
trols, check the TRIGGERING COUPLING and SOURCE
switch settings.

Operating Instructions—7B80
Mainframe Operating Modes
The time-base unit can be operated either as an indepen-
dent time base in any Tektronix 7700-, 7800-, or 7900-
series oscilloscope mainframe, or as adelayed-sweep unit in
those mainframes that have two horizontal compartments.
Acompanion delaying time-base unit is required for delayed-
sweep operation. Refer to the delaying time-base unit in-
struction manual for additional information.
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Fig. 1-4. Area of graticule used for most accurate time measure-
ments. Fig. 1-5. Operation of sweep magnifier.

Operating Instructions—7B80
APPLICATIONS
The following information describes procedures and techniques for making basic time measurements with the time-base unit
installed in aTektronix 7700-, 7800-, or 7900-series oscilloscope. These procedures provide enough detail to enable the
operator to adapt them to other related time measurements. Contact your Tektronix Field Office or representative for
assistance in making measurements that are not described in this manual.
TIME-INTERVAL MEASUREMENTS
Since time is afunction of the sweep rate and the horizon-
tal distance (in divisions) that the sweep travels across the
graticule in acalibrated-sweep oscilloscope system, the time
interval between any two points on awaveform can be
accurately measured. The following procedures provide
methods to measure some of the more common time-
related definable characteristics of awaveform such as
period, frequency, rise time, fall time, and pulse width. The
procedure for each of these measurements is essentially the
same, except for the points between which the measure-
ments are made. The time interval between any two
selected points on adisplayed waveform can be measured
with basically the same technique.
Period and Frequency Measurements
Perform the following procedure to measure the period and
determine the frequency of adisplayed waveform:
1.
Install the time-base unit in amainframe horizontal
compartment (either Aor Bhorizontal in a four-compart-
ment mainframe).
7. Measure the horizontal distance in divisions over 1com-
plete cycle of the displayed waveform (see Figure 1-6).
8. Multiply the horizontal distance measured in Step 7by
the TIME/DIV switch setting. (Divide the answer by 10 if
sweep magnification is used.)
Example: Assume that the horizontal distance over 1com-
plete cycle is 7divisions, and the TIME/DIV switch setting
is .1 ms (see Figure 1-6).
Using the formula:
Period =Florizontal distance XTIME/DIV setting
Magnification
Substituting values:
Period =7X0.1 ms =0.7 millisecond
1
2.
Connect the signal to be measured to the vertical unit
input.
3. Set the mainframe horizontal- and vertical-mode switch-
es to display the time base and vertical units. (Check that
the time base VARIABLE (CAL IN) control is pushed in
and the HOLD OFF control is in the MIN position.)
4. Set the TRIGGERING switches and LEVEL control for
astable display (see General Operating Information for
selecting proper triggering).
5. Set the vertical deflection factor and position control
for about a5-division display, vertically centered on the
graticule.
6. Set the TIME/DIV switch and POSITION control for 1
complete cycle displayed within the center 8graticule divi-
sions as shown in Figure 1-6. Fig. 1-6. Measuring the period and determining the frequency of a
displayed waveform.

Operating Instructions—7B80
9. Determine the frequency of the displayed waveform ob-
tained in steps 1through 8by taking the reciprocal of the
period of 1cycle.
Example: Assume that the period of the displayed wave-
form is 0.7 millisecond.
Using the formula:
Frequency =1
Period
Substituting values:
Frequency =1=1.43 kilohertz
0.7 ms
Rise-Time and Fall-Time Measurements
Perform the following procedure to measure the rise time
and fall time of adisplayed waveform:
1.
Install the time-base unit in amainframe horizontal
compartment (either Aor Bhorizontal in afour-compart-
ment mainframe).
2.
Connect the signal to be measured to the vertical unit
input.
3.
Set the mainframe horizontal- and vertical-mode switch-
es to display the time base and the vertical unit. (Check
that the time base VARIABLE (CAL IN) control is pushed
in and the HOLD OFF control is in the MIN position.)
4.
Set the TRIGGERING switches and LEVEL control for
astable display (see General Operating Information for
selecting proper triggering).
5.
Set the vertical deflection factor and position control
for avertically-centered display with an exact number of
divisions of amplitude.
6.
Set the TIME/DIV switch and POSITION control to dis-
play the rising or falling portion of the waveform within the
center 8graticule divisions as shown in Figure 1-7 (see
General Operating Information in this section for discussion
of timing measurement accuracy).
7.
Determine rise time or fall time by measuring the hori-
zontal distance in divisions between the point on the rising
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Fig. 1-7. Measuring the rise time and fall time of adisplayed wave-
form.
or falling portion of the waveform that is 10% and the
point that is 90% of the total display amplitude (see Figure
1-7).
NOTE
The left edge of the oscilloscope graticule is
scribed with 0, 10, 90, and 100% lines for con-
venience when measuring rise time or fall time.
To use this feature, adjust the vertical deflection
factor and position control to fit the display be-
tween the 0and 100% graticule lines. Then
measure the horizontal distance between the
points where the waveform crosses the 10% and
90% graticule lines.
@1-11

Operating Instructions—7B80
8. Multiply the horizontal distance measured in step 7by
the TIME/DIV switch setting. (Divide the answer by 10 if
sweep magnification is used.)
8. Multiply the horizonal distance measured in step 7by
the TIME/DIV switch setting. (Divide the answer by 10 if
sweep magnification is used.)
Example: Assume that the horizontal distance from the 10
to 90% points is 2.5 divisions and the TIME/DIV switch set-
ting is .1 /is (see Figure 1-7).
Example: Assume that the horizontal distance between the
50% amplitude points is 3divisions, and the TIME/DIV
switch setting is .1 ms (see Figure 1-8).
Using the formula:
Horizontal distance
Rise Time -(divisions)
Magnification
TIME/DIV
setting
Substituting values:
Rise Time =2.5x0.1jUs =0.25 microsecond
1
Pulse Width Measurements
Perform the following procedure to measure the pulse
width of adisplayed waveform:
1.
Install the time-base unit in amainframe horizontal
compartment (either Aor Bhorizontal in afour-compart-
ment mainframe).
2.
Connect the signal to be measured to the vertical unit
input.
3.
Set the mainframe horizontal- and vertical-mode
switches to display the time base and vertical unit. (Check
that the time base VARIABLE (CAL IN) control is pushed
in and the HOLD OFF control is in the MIN position.)
4.
Set the TRIGGERING switches and LEVEL control
for astable display (see General Operating Information for
selecting proper triggering).
5,
Set the vertical deflection factor and position control
for about a5-division pulse vertically centered on the
graticule.
6.
Set the TIME/DIV switch and POSITION control for 1
complete pulse displayed within the center 8graticule divi-
sions as shown in Figure 1-8.
7.
Measure the horizontal distance in divisions between the
50% amplitude points of the displayed pulse (see Figure
1-8).
Using the formula:
Pulse Width Horizontal
distance
TIME/DIV
setting
Magnification
Substituting values:
Pulse Width =3X0.1 ms =0.3 millisecond
1
DELAYED-SWEEP MEASUREMENTS
The time-base unit may be used with adelaying time-base
unit in amainframe with two horizontal compartments to
make delayed-sweep measurements. See the Tektronix
Products Catalog for compatible delaying time-base plug-in
units. If acompatible delaying time-base unit is available,
refer to the instruction manual for that unit for detailed
delayed-sweep measurement procedures.
X-Y PHASE MEASUREMENTS
The phase difference between two signals with the same fre-
quency can be measured with a7B80 Option 2and ampli-
fier plug-in units. Refer to the Instrument Options section
of this manual for detailed procedures.
PULSE WIDTH
Fig. 1-8. Measuring the pulse width of adisplayed waveform.