Tektronix 7B87 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon
070-2788-00
Product Group 42
Tektronix:
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7B87
TIME BASE
WITH
PRETRIGGER
ACQUIRE CLOCK
INSTRUCTION MANUAL
97077 Serial Number —
First Printing APR 1980
Revised JAN 1986

Copyright © 1980 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. TELEQUIPMENT
is a registered trademark of Tektronix U.K. Limited.
Printed in U.S.A. Specification and price change privileges
are reserved.
INSTRUMENT SERIAL NUMBERS
Each instrument has a serial number on a pariel insert, tag,
or stamped on the chassis. The first number or letter
designates the country of manufacture. The last five digits
of the serial number are assigned sequentially and are
unique to each instrument. Those manufactured in the
United States have six unique digits. The country of
manufacture is identified as follows:
B000000 Tektronix, Inc., Beaverton, Oregon, USA
100000 Tektronix Guernsey, Ltd., Channel Islands
200000 Tektronix United Kingdom, Ltd., London
300000 Sony/Tektronix, Japan
700000 Tektronix Holland, NV, Heerenveen,
The Netherlands

7B87 Instruction
TABLE OF CONTENTS
PAGE
UST OF ILLUSTRATIONS ..
LIST OF TABLES ........
OPERATORS SAFETY SUMMARY
SERVICING SAFETY SUMMARY .
SECTION 1—-OPERATING INSTRUCTIONS
INSTALLATION .
CONTROLS, CONNECTORS, AND INDICATORS
FUNCTIONAL CHECK ..
SETUP PROCEDURE
SWEEP FUNCTIONS...
TRIGGERING FUNCTIONS
PRETRIGGER ACQUIRE CLOCK FUNCTIONS
GENERAL OPERATING INFORMATION
TRIGGERING SWITCH LOGIC .
TRIGGERING MODES
TRIGGER COUPLING .
TRIGGER SOURCE .
TRIGGER SLOPE .
TRIGGER LEVEL .
HORIZONTAL SWEEP RATES .
TIME MEASUREMENT.......
SWEEP MAGNIFICATION .
VARIABLE HOLD OFF .. tee *
MAINFRAME OPERATING MODES . 1-12
APPLICATIONS .......+--200eee ees
TIME INTERVAL MEASUREMENTS . a
PERIOD AND FREQUENCY MEASUREMENTS ...
RISE-TIME AND FALL-TIME MEASUREMENTS
PULSE WIDTH MEASUREMENTS...............
CORDOHEES
HHS
SECTION 2--SPECIFICATION
STANDARD ACCESSORIES ......
[wannine )
THE REMAINING PORTION OF THIS TABLE OF CONTENTS
LISTS SERVICING 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 INSTRUCTIONS UNLESS QUALIFIED TO DO
so.
SECTION 3--THEORY OF OPERATION
BLOCK DIAGRAM DESCRIPTION
TRIGGER GENERATOR ....
SWEEP GENERATOR
PICKOFF AMPLIFIER AND DELAY GATE
DIGITAL VOLTMETER .
CLOCK GENERATOR ..
REV JUN 1981
DETAILED CIRCUIT DESCRIPTION ..
FRONT-PANEL DISTRIBUTION
TRIGGER GENERATOR ..
EXTERNAL SOURCE.
INTERNAL AND LINE SOURCE
TRIGGER SOURCE SELECTOR AND
AMPLIFIER ...
PEAK-TO-PEAK AUTO.
SLOPE
SELECTOR AND TRIGGER
GENERATOR .
GATE GENERATOR
SSSI
Oooo
SWEEP MODES
HOLD OFF TIMING . +
LOCKOUT BUFFER AMPLIFIER .
HOLD OFF OUTPUT AMPLIFIER.
SWEEP GENERATOR.........
TIMING CURRENT SOURCE
RAMP GENERATOR .......
HORIZONTAL PREAMPLIFIER
SWEEP GATE GENERATOR . z
DVM occ vcscccescectecceescencetoccoeeressoeseee 3-10
DELAY TIME COMPARATOR AND DELAY
GATE GENERATOR
DIGITAL VOLTMETER .
DELAY COMPARISON VOLTAGE-TO-RAMP
CONVERTER
COMPARATOR
REFERENCE CURRENT SOURCE .
REFERENCE CURRENT INVERTER
COUNTER AND ENCODER .
CLOCK GENERATOR
CONTROL LOGIC
OSCILLATOR ..
FIRST DIVIDER .
X1-X10 MULTIPI
DECADE DIVIDER .
INTERNAL CLOCK MULTIPLEXER
OUTPUT CLOCK MULTIPLEXER
INTENSIFY CIRCUIT
7887 IN A HORIZ PLUG-IN COMPARTMENT “
INTERNAL BUTTON PRESSED......
7887 IN B HORIZ PLUG-IN COMPARTMENT .
INTERNAL BUTTON PRESSED..........
TIME/DIVISION AND READOUT SWITCHING .
BASIC READOUT SYSTEM .
TIME/DIVISION READOUT.
ACQUIRE-STOP DELAY TIME READOUT
INTERFACE CONNECTIONS AND POWER
SUPPLY ciivesedccececseveeevevessses asesee S47
SECTION 4-—-MAINTENANCE
PREVENTIVE MAINTENANCE ...
CLEANING....
EXTERIOR ....
INTERIOR...
SWITCH CONTACTS

TROUBLESHOOTING ........
CORRECTIVE MAINTENANCE ......
ADJUSTMENT AFTER REPAIR
7B87 Instruction
TABLE OF CONTENTS (CONT)
VISUAL
INSPECTION . 41
LUBRICATION a 41
CAM SWITCH LUBRICATION. 4-2
SEMICONDUCTOR CHECKS .. wesses MEQ
ADJUSTMENT AFTER REPAIR
TROUBLESHOOTING AIDS 4-2
DIAGRAMS . 42
VOLTAGES AND WAVEFORMS. * 4-2
CIRCUIT-BOARD ILLUSTRATIONS ... 4-2
SWITCH CAM IDENTIFICATION .. 44
DIODE COLOR CODE..
WIRING COLOR CODE oe
SEMICONDUCTOR LEAD CONFIGURATIONS .....
INTER-BOARD PIN CONNECTOR
IDENTIFICATION
MULTI-PIN CONNECTOR IDENTIFICATION .
INTERFACE CONNECTOR PIN LOCATIONS .
PERFORMANCE CHECK AND ADJUSTMENT .
STATIC SENSITIVE DEVICES ....
TROUBLESHOOTING EQUIPMENT.....
TROUBLESHOOTING TECHNIQUES.....
TROUBLESHOOTING PROCEDURE .
OBTAINING REPLACEABLE PARTS ..
SOLDERING TECHNIQUES........ 5 z
COMPONENT REMOVAL AND REPLACEMENT
CIRCUIT BOARDS
SWITCHES
SEMICONDUCTORS .
INTERCONNECTING PINS.
CIRCUIT-BOARD PINS .
FRONT-PANEL LIGHTS ..
INSTRUMENT REPACKAGING .
PAGE
SECTION 5--PERFORMANCE CHECK AND
ADJUSTMENT
PRELIMINARY INFORMATION
ADJUSTMENT INTERVAL .
TEKTRONIX FIELD SERVICE.
USING THIS PROCEDURE
TEST EQUIPMENT REQUIRED . .
SPECIAL FIXTURES
TEST EQUIPMENT ALTERNATIVES.
INDEX TO PERFORMANCE CHECK AND
ADJUSTMENT PROCEDURE ..
PRELIMINARY PROCEDURE
A. TRIGGERING SYSTEM ...
B. HORIZONTAL/AQS SYSTEM .
SECTION 6—!INSTRUMENT OPTIONS
SECTION 7 REPLACEABLE ELECTRICAL PARTS
SECTION 8--DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
SECTION 9—REPLACEABLE MECHANICAL PARTS
CHANGE INFORMATION
REV JUN 1981

FIG.
NO.
Frontis.
piece
1-
1
1
iF
3
4
No
1
2
7B87 Instruction
LIST OF ILLUSTRATIONS
PAGE
7887 Features........
Location of release latch.
Front-panel controls, connectors, and
INDIO wi vcs sssansuese ees earcceanes 1-2
Single Sweep Acquisition.........6.-066s000e005 15
Effect of LEVEL control and SLOPE switch
on crt display
Area of graticule used for most accurate
time measurements
Operation of sweep magnifier
Measuring the period and determining the
frequency of a displayed waveform ............. 1-13
Measuring the rise time and fall time of
a displayed waveform ...........0000seseeeees 1.14
Measuring the pulse width of a displayed
waveform
7887 dimensional drawing
Basic block diagram of the 7887 Delaying
Time Base Unit
Detailed block diagram of Trigger Generator
Timing diagram for Gate Generator stage
(292, 096, 98)
Detailed block diagram of Logic circuit .
Detailed block diagram of Sweep Generator .
Timing of events that form the Delay
Gate signal
Lubrication procedure for a typical
CAM SWICH wicks cuovuvcri macevacsansaveseroavee
Semiconductor lead configuration
Inter-board multi-pin connector assembly .
REV JUN 1981
FIG.
PAGE
NO.
44 End-lead multi-pin connector assembly .......... 44
45 Location of pin numbers on Interface
connector
4-6 7887 troubleshooting chart .
47 Readout board removal procedure ..
48 Coaxial end-lead connector assembly .
49 Location of securing screws and inter-board
multi-pin connectors on clock circuit board. ..... 4-12
4-10 Cam switch removal procedure ..........0-45+5 4-13
Removal procedure for typical pushbutton
switch
4-12 Exploded view of circuit-board pin and
ferrule
The illustrations in Section 8 are located near their associated
diagrams on the foldout pages.
1 Semiconductor Lead Configurations
2 Locations of circuit boards in the 7B87.
3 A2-Trigger circuit board assembly
4 A1-Interface circuit board assembly
5 A1-Interface circuit board assembly
-6 A1-Interface circuit board assembly
7 A4-Clock circuit board assembly
8 A4-Clock circuit board assembly.
3 A3-Readout circuit board assembly,
1 A1-Interface circuit board assembly
1 Test Point and Adjustment Locations =o

7887 Instruction
LIST OF TABLES
PAGE
TIME/DIV Setting Relationship To 7887
Internal Acquire Clock Rep Rate .
Electrical Characteristics .
Mainframe Horizontal Compatibility
Environmental Characteristics .... ae
Physical Characteristics ............00eeeeee eee
Truth Table, TIME/DIV Setting vs. Strobes
for U637 and U63B oo... ee eeeeeeeeeeeee eens
Selected Inputs or X1 and X10 Multiplexers.
Operation of Output Multiplexer U655 ...
Current in CH1 Readout Line vs. Acquire
Clock Mode, During TS10. ..
Readout Character Selection
Relative Susceptibility .
Test Equipment .....
Acquire Clock Repetition Rate Output.
Delay Time Linearity
Acquire-Stop Delay Accuracy . 6-13
Sweep Timing .
Magnified Sweep Timing .

7887 Instruction
OPERATORS SAFETY SUMMARY
The general safety information in this part of the summary is for both operating and servicing personnel. Specific
warnings and cautions will be found throughout the manual where they apply, but may not appear in this summary.
TERMS
IN THIS MANUAL
CAUTION statements identify conditions or practices that could result in damage to the equipment or other property.
WARNING statements identify conditions or practices that could result in personal injury or loss of life.
AS MARKED ON EQUIPMENT
CAUTION indicates a personal injury hazard not immediately accessible as one reads the marking, or a hazard to
property including the equipment itself.
DANGER indicates a personal injury hazard immediately accessible as one reads the marking.
SYMBOLS
IN THIS MANUAL
® Static-Sensitive Devces.
A This symbol indicates where applicable cautionary or other information is to be found.
AS MARKED ON EQUIPMENT
4 DANGER—High voltage.
© Protective ground (earth) terminal.
A ATTENTION—refer to manual
WARNINGS
POWER SOURCE
This product is intended to operate in a mainframe connected to a power source that will not apply more than 250 volts
rms between the supply conductors or between either supply conductor and ground. A protective ground connection by
way of the grounding conductor in the mainframe power cord is essential for safe operation.
GROUNDING THE PRODUCT
This product is grounded through the grounding conductor of the mainframe power cord. To avoid electrical shock, plug
the mainframe power cord into a properly wired receptacle before connecting to the product input or output terminals. A
protective ground connection by way of the grounding conductor in the mainframe power cord is essential for safe
operation.

7B87 Instruction
DANGER ARISING FROM LOSS OF GROUND
Upon loss of the protective-ground connection, all accessible conductive parts (including knobs and controls that may
appear to be insulating), can render an electric shock.
DO NOT OPERATE IN EXPLOSIVE ATMOSPHERES
To avoid explosion, do not operate this product in an atmosphere of explosive gases unless it has been specifically
certified for such operation.
DO NOT OPERATE PLUG-IN UNIT WITHOUT COVERS
To avoid personal injury, do not operate this product without covers or panels installed. Do not apply power to the plug-in
unit via a plug-in extender.
vi

7887 Instruction
SERVICING SAFETY SUMMARY
FOR QUALIFIED SERVICE PERSONNEL ONLY
Refer also to the preceding Operators Safety Summary
DO NOT SERVICE ALONE
Do not perform internal service or adjustment of this product unless another person capable of rendering first aid and
resuscitation is present.
USE CARE WHEN SERVICING WITH POWER ON
Dangerous voltages exist at several points in this product. To avoid personal injury, do not touch exposed connections
and components while power is on.
Disconnect power before removing protective panels, soldering, or replacing components.
POWER SOURCE
This product is intended to operate in a mainframe connected to a power source that will not apply more than 250 volts
rms between the supply conductors or between either supply conductor and ground. A protective ground connection by
way of the grounding conductor in the mainframe power cord is essential for safe operation,
vii

7B87 Instruction
eee
eenene
. TIME BASE =o
W/PRETRIGGER
ACQUIRE
CLOCK)
2788.1
7B87 FEATURES
The 7887 Time-Base unit Pretrigger Acquire Clock provides calibrated sweep rates from 5 seconds to 10 nanoseconds and triggering to 400
megahertz for 7000-Series Oscilloscopes. A X10 Magnifier increases each sweep rate by a factor of 10 and a VARIABLE TIME/DIV control
provides continuously-variable sweep rates between calibrated steps. Variable holdoff and alphanumeric readout are provided. Also, when
operating in the AUTO TRIGGERING MODE, a bright baseline trace is displayed in the absence of a trigger signal. The 7B87 can be operated
as an independent time base or as a delayed-sweep unit with a companion delaying time-base unit. Sweep mode is determined by the
companion delaying time base
The
7887 also features an internally-generated clock and an external clock input for sequential single sweep acquisition when operating ina
7000-series digitizing oscilloscope. The frequency range of the internally generated clock is 20.48 mHz (millihertz) to 20.48 MHz as
determined by the TIME/DIV, X10 MAG, and INT = 1000 switches. Also, an ACQUIRE-STOP DELAY function varies delay pickoff, and
therefore pretrigger time, in compatible digitizing plug-in oscilloscopes. The portion of the oscilloscope real-time display between the
triggering event and the end of delay time is intensified. The exact delay time is displayed on the crt readout

Section 1—7B87
OPERATING INSTRUCTIONS
The 7B87 Time-Base unit operates with a Tektronix 7700-, 7800-, or 7900-series oscilloscope mainframe and a 7A-
series amplifier unit to form a complete oscilloscope system. This section describes the operation of the front-panel
controls and connectors, provides general operating information, a functional check procedure, and basic applications for
this instrument.
INSTALLATION
The time-base unit operates in the horizontal plug-in
compartment of the mainframe. When used for single
sweep acquisition with a Tektronix 7000-series digitizing
oscilloscope (7854) the 7B87 must be installed in the B
horizontal compartment of the mainframe. This
instrument can also be installed in a vertical plug-in
compartment to provide a vertical 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 specifications given in Section 2,
Specification.
To install the unit in a plug-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 installed. The procedure for checking the
unit is given under Sweep Functions in the Functional
Check procedure in this section.
To remove the unit, first turn the power off, then pull the
release latch (see Fig. 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 a brief 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
controls, connectors, and indicators while performing
this procedure. If performing the functional check
procedure reveals a malfunction or possible improper
adjustment, first check the operation of the associated
plug-in units, then refer to the instruction manual for
maintenance and adjustment procedures.
SETUP PROCEDURE
1. Install the time-base unit in the A horizontal
compartment of the mainframe.
2. Install an amplifier plug-in unit in a vertical
compartment.
3. Set the time-base unit controls as follows:
SOURCE .
POSITION Midrange
TIME/DIV ... vee Ms
VARIABLE (CAL IN) : Calibrated (Pushed in)
HOLD OFF.......... MIN (fully counterclockwise)
MAGE siicicninseresnareewin ees X1 (pushed in)
ri ee
i ome om oe ||)
|
}
{
i
\
| |
||
UY 7687") ttetmence atime coe
RELEASE
LATCH 2788.2
Figure 1-1. Location of release latch.
1-1

Operating Instructions 7B87
TRIGGERING
MODE COUPLING SOURCE
PP AUTO nT
lon
7887
‘AGS CLOCK/AGR wm || x1
our || x10
= INTERNAL
{El uviaen
9
‘5
ACQUIRE-STOP DELAY |p
@*&S
EXT CLOCK IN
© °
WOOK Vgs5v
owren te
met Ch
our=0 = I)
EXT TRIG IN
©
TIME BASE mo
W/PRETRIGGER ACQUIRE CLOCK
Figure 1-2. Front-panel controls, connectors, and indicators.
1-2

Operating Instructions—7B87
TRIGGERING
©) LEVEL Control—Selects a point 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—Ililuminates when sweep circuit is armed (SINGLE SWEEP Mode).
® TRIG'D Indicator —I!luminates 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- 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.
PRETRIGGER ACQUIRE CLOCK
@) AQS (acquire single-shot) CLOCK/AQR (acquire repetitive) Selects the source of clock pulses from the 7887 to
the 7854 digitizing plug-in oscilloscope (7887 must be installed in B horizontal compartment of companion
oscilloscope mainframe)
(18) AcaUIRE-STOP DELAY Control— A variable delay gate function that allows pretrigger time tobe varied in compatible
7000-series digitizing oscilloscopes. Exact delay time is displayed on oscilloscope crt readout
EXT CLOCK IN Connector—-Provides input for external TTL clock signals.
2788 38
Figure 1-2 (cont). Front-panel controls, connectors, and indicators.
1-3

Operating Instructions—7B87
4. Turn on the mainframe and allow at least 20 minutes
warmup.
5. Set the mainframe vertical and horizontal modes to
display the plug-in units used and adjust the intensity
and focus for a well-defined display. See the oscilloscope
mainframe and amplifier unit instruction manuals for
detailed operating instructions.
SWEEP FUNCTIONS
NORMAL SWEEP. Perform the following procedure to
obtain a normal sweep and to demonstrate the function
of the related controls:
1. Perform the preceding Setup Procedure.
2. Connect a 0.4-volt, 1-kilohertz signal from the
mainframe calibrator to the amplifier unit input.
3. Set the amplifier unit deflection factor for 4 divisions
of display.
4. Adjust the LEVEL control for a stable 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
adjustment for one complete cycle per division over the
center 8 graticule 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) contro! fully counterclockwise
and note that the displayed sweep rate changes to at
least the next slower TIME/DIV switch setting (i.e., 2
milliseconds/division). Press the VARIABLE (CAL IN)
knob in (to the calibrated position).
MAGNIFIED SWEEP. Perform the following procedure
to obtain a X10 magnified display and to demonstrate the
function of the related controls:
1. Obtain a one 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
graticule is magnified to about 10 divisions.
3. Press the MAG button (X1).
1-4
TRIGGERING FUNCTIONS
Perform the following procedure to obtain a triggered
sweep and to demonstrate the functions of the related
controls:
1. Obtain a display as described in the preceding Normal
Sweep procedure.
2. Press the AUTO MODE button and turn the LEVEL
control fully counterclockwise to obtain a free-running
sweep.
3. Slowly turn the HOLD OFF control clockwise and note
that a stable 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 primary 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 a stable display (LEVEL control may be
adjusted, if necessary, to obtain a stable display).
5. Apply the 0.4-volt, 1-kilohertz signal from the
mainframe 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 a 4-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 a stable display (LEVEL control may be
adjusted, if necessary, for a stable display),
8. Press the AC COUPLING, INT SOURCE, and NORM
MODE buttons. Adjust the LEVEL control for a stable
display.
9. Press the AUTO MODE button and adjust the LEVEL
control for a free-running display.
10. Press the NORM MODE button and check for no
display.
11. Adjust the LEVEL control for a stable 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
indicator extinguishes when the mainframe calibrator
signal is reconnected to the amplifier unit input.
PRETRIGGER ACQUIRE CLOCK FUNCTIONS
NOTE
The following procedure must be performed
with the 7887 installed in the B horizontal
compartment of a Tektronix 7854
Oscilloscope.
1. Install the 7B87 in the 7854 Oscilloscope B horizontal
compartment and install an amplifier unit in the
mainframe left vertical compartment. Turn on
oscilloscope power. See Tektronix 7854 Oscilloscope
Operators Manual for detailed operating information.
2. Set the time-base unit controls as follows:
SLOPE ..
MODE ..
COUPLING .
SOURCE ..
POSITION .
TIME/DIV .
VARIABLE .
HOLDOFF .
MAG .....
MIN (fully counterclockwise)
» X1 (pushed in)
INTERNAL
ACQUIRE STOP DELAY . Midrange
3. Set the 7854 vertical and horizontal modes to display
the plug-in units and set WFM ACQUISITION to SCOPE.
Set the intensity and focus for a well-defined, intensified
display.
4. Connect the 0.4-volt, 1-kilohertz signal from the
mainframe calibrator to the amplifier unit input.
5. Set the amplifier unit deflection factor for 4 divisions
of display.
6. Set the TRIGGERING MODE to NORM and adjust the
LEVEL control for a stable display (TRIG’D light on).
7. Rotate the ACQUIRE-STOP DELAY control fully
counterclockwise. Notice that delay-time readout (located
in the lower right-hand corner of the crt) is near 0.2 ms.
(Zero delay time means that the acquired signal occurred
prior to the triggering event.)
8. Rotate the ACQUIRE-STOP DELAY contro! until the
delay-time readout is approximately 4 ms. Notice that the
first four divisions of squarewave display are intensified.
The 4 ms intensified display relates to four divisions of
post-trigger in the subsequent single-sweep display.
Therefore, the remaining 6 divisions in the subsequent
display would be pre-trigger (see Fig. 1-3).
Operating Instructions—7B87
NOTE
Four divisions of intensified display at 1
ms/div relates to delay-time readout of
approximately 4 ms.
9. Set the amplifier unit input coupling switch to off or
ground. Set the 7B87 to SINGLE SWEEP MODE and
press the RESET pushbutton so that READY light is on.
10. Set the 7854 to Stored CRT Display and then to
Acquire Single-Shot Waveform Acquisition (AQS).
INTENSIFIED ZONE
POST-TRIGGER.,, SCOPE (REAL-TIME) MODE
r TIME SWEER SPEED
Tonv
|r riccer
YT _PoInt STOP
eel Sian is
|
E f 4
—
ACQUIRE—STOP DELAY TIME See ge4ns
(POST-TRIGGER TIME)
(A) 7854 REAL-TIME DISPLAY (SCOPE MODE)
PRE-TRIGGER TIME IN
THE 7887 INTERNAL —-1,POST TRIGGER
Pr AQS CLOCK MODE
pu le juzr fe ft Ins |
a } 1
|... SINGLE SWEEP _| | ACQUIRE
“| trigger point stop
| |
EBS p
ip |
i
[ |
t i
(B) 7854 STORED SINGLE SWEEP DISPLAY.
2788 6
Figure 1-3. Single Sweep Acquisition.

Operating Instructions—7B87
11. To trigger the single-sweep display, set the amplifier
unit input coupling to de. Triggering occurs when the
amplifier coupling switch is set to dc. The first six
milliseconds of the display is pretrigger. (Noise in the
Stored Single Sweep may be displayed at the Single
Sweep Trigger Point as a result of the coupling switch
contact closure.)
GENERAL OPERATING
INFORMATION
TRIGGERING SWITCH LOGIC
The MODE, COUPLING, and SOURCE pushbuttons of the
TRIGGERING switches are arranged in a sequence which
places the most-often used position at the top of each
series of pushbuttons. With this arrangement, a stable
display can usually be obtained by pressing the top
pushbuttons: 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 TRIG’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 inadequate, 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 pushbutton switches select the mode in
which the sweep is triggered.
P-P AUTO. The P-P AUTO MODE provides a triggered
display at any setting of the LEVEL control whenever an
adequate 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 a certain percentage point on the
leading edge of a low-amplitude signal, it also triggers at
the same percentage point on the leading edge of a high-
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 a bright
base-line, reference trace (TRIG’D light off). When an
adequate trigger signal is again applied, the free-running
condition ends and a triggered display is presented.
The P-P AUTO MODE is particularly useful when
observing a series 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
1-6
ease of obtaining a triggered display. The AUTO, NORM,
and SINGLE-SWP MODE settings may be used for
special applications.
AUTO. The AUTO MODE provides a triggered display
with the correct setting of the LEVEL control whenever
an adequate trigger signal is applied (see Trigger Level
discussions). 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
signal is inadequate, the sweep free runs at the rate
indicated by the TIME/DIV switch (TRIG’D indicator off).
An adequate 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 a setting 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 a signal without
observing the waveshape (such as bandwidth
measurements).
NORMAL. The NORM MODE provides a_ triggered
display with the correct setting of the LEVEL control
whenever an adequate trigger signal is applied. The
TRIG’D light indicates when the display is triggered.
The normal trigger mode must be used to produce
triggered displays with trigger repetition rates below
about 30 hertz. When the TRIG'D light is off, no trace is
displayed.
SINGLE-SWEEP OPERATION. The 7B87 single-sweep
function can be used with both digitizing and non-
digitizing oscilloscopes. A discussion of each follows:
Non-Digitizing Oscilloscope Single Sweep. When the
signal to be displayed is not repetitive or varies in
amplitude, waveshape, or repetition rate, a conventional
repetitive type display may produce an_ unstable
presentation, Under these circumstances, a_ stable
display can often be obtained by using the single-sweep
feature of this unit. The single-sweep mode is useful to
photgraph non-repetitive or unstable displays.
To obtain a single-sweep display of a repetitive signal,
first obtain the best possible display in the NORM MODE.
Then, without changing the other TRIGGERING controls,
press the SINGLE SWP RESET button. A single trace is
presented each time this button is pressed. Further
sweeps cannot be presented until the SINGLE SWP.
RESET button is pressed again. If the display signal is a
complex waveform composed of varying amplitude
pulses, successive single-sweep displays may not start at
the same point on the waveform. To avoid confusion due
to the crt persistance, allow the display to disappear
before pressing the SINGLE SWP RESET button again. At
fast sweep rates, it may be difficult to view the single-
sweep display. The apparent trace intensity can be
increased by reducing the ambient light level or by using
a viewing hood as recommended in the mainframe
instruction manual.

When using the single-sweep mode to photograph
waveforms, 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 a
darkened room. For repetitive waveforms, press the
SINGLE SWP RESET button only once for each waveform
unless the signal is completely symmetrical. Otherwise,
multiple waveforms may appear on the film. For random
signals, the camera shutter can be left open until the
signal triggers the unit. Further information on
photographic techniques is given in the appropriate
camera instruction manual.
Single-Sweep Acquisition Using a 7854 Oscilloscope.
The ACQUIRE-STOP DELAY control and AOS CLOCK
switches function only with the 7B87 installed in the
7854 Oscilloscope B Horiz compartment. The 7854
requires a sequential clock signal to acquire a single-
sweep display: this is provided by the 7B87 time-base
unit with the AQS CLOCK/AQR clock switch in the
INTERNAL or INT = 1000 positions or externally through
the EXT CLOCK IN, when in the EXT/AQR position.
Table 1-1 shows the internal clock frequencies at
different TIME/DIV switch settings, at X10 MAG settings
and at the INTERNAL and INT = 1000 settings of the AQS
CLOCK/AQR switches
Operating Instructions--7B87
1. INTERNAL. The clock is generated internally, with the
clock frequency determined by the TIME/DIV and MAG
settings (see Table 1-1).
The ACQUIRE-STOP DELAY control varies the allocation
of pretrigger and post-trigger time in the subsequent
stored single-sweep display. The post-trigger portion is
intensified in the real-time display and the exact time is
displayed by CRT readout (see Fig. 1-3).
NOTE
Occasionally, when using the 7B87/7854, the first
point of single-shot acquired (AQS) waveform will be
displayed at the end of the trace (extreme right) and
will appear that the waveform has made a transition
on the last point. To determine if the last point is
erroneous, check that the first and last points have
nearly the same vertical value at any setting of the
7887 ACQUIRE-STOP DELAY control.
2. INT + 1000—In this AQS CLOCK mode the internal
clock frequency is divided by 1,000 (see Table 1-1). The
real-time display is the same as the internal mode with
the intensified zone and associated ACQUIRE-STOP
The AQS CLOCK/AQR switches select three clock DELAY readout corresponding to post-trigger time in the
operating modes: subsequent stored single-sweep display.
TABLE 1-1
TIME/DIV Setting Relationship To
7B87 Internal Acquire Clock Rep Rate
7 a ees ee ee ease
ee MAG _
TIME/DIV x7 x1 X1 + 1000 x10 = 1000
204.8 Hz 02048 He 2088 He
512 Hz ‘512 He __
1024 Hz 1.024 He _
_ 2. 048 kHz 7 2.048 Hz
"5.12 kHz 5.12 Hz
10.24 kHz | 10.24 Hz _
20.48 kHz 20.48 Hz
51.2 kHz 51.2 Hz |
10.24 kHz 102.4 kHz | | 102.4 He
20.48 kHz 204.8 kHz 204.8 Hz
51.2 kHz 512 Hz
kHz 1.024 kHz
_ ki 2.048 MHz 2.048 kHz
512 kHz "6.12 MHz | 5.12 kHz
1.024 MHz _ “10.24 MHz 1.024 kHz 10.24 kHz
2.048 MHz 20.48 MHz 2.048 kHz 20.48 kHz
6.12 MHz 5.12 kHz —
10.24 MHz - 10.24 kHz __
REV A MAR 1981

Operating Instructions—7B87
The AQS stored single-sweep display is effectively 1000
times slower than the real-time display; however, the
ACQUIRE-STOP DELAY time (post-trigger time) remains
unchanged and becomes insignificant compared to the
digitized sweep. Therefore, the stored single-sweep
display is for practical purposes all pretrigger.
NOTE
During single-shot acquisition with an external clock
input the 7854 may not necessarily sample one data
point for each clock pulse, as shown below:
P/W (Points/ Clock Pulses
Waveform) Required
1024 1
- 512 2
2 56 4
128 8
3. EXT/AQR (EXT CLOCK IN)—This mode connects the
external TTL compatible clock signal, applied to the front-
panel EXT CLOCK IN connector, to the companion
digitizing oscilloscope mainframe (7854).
The real-time display is the same as the internal mode
with the intensified zone and associated ACQUIRE-STOP
DELAY readout corresponding to post-trigger time in the
subsequent stored single-sweep display. When the AQS
(acquire single-shot) display is stored, the ACQUIRE-
STOP DELAY time is as displayed on the readout but the
effective TIME/DIV of the display changes at a rate
determined by the frequency of the external clock signal.
The resulting TIME/DIV for the stored single-sweep
display acquired in the external clock mode can be
determined by the following formula:
1-8
EXT TIME/DIV = 102.4 x External Clock Period
or
=. eeenrereaes
102.4 * EXT CLOCK FREQUENCY
NOTE
The 7854 may not return from the acquire single-shot
(AQS) mode if the acquire-stop occurs before the
memory is filled once. This is most noticeable at slow
sweep speeds, especially in the internal +1000 clock
mode. When the 7854 AQS button is pressed, the
7854 begins to sample the waveform and fill the
memory. The acquire-stop signal occurs at a set
interval after the 7B87 is triggered, this interval is the
acquire-stop delay time. If the acquire-stop is
generated before the 7854 has filled the memory
once (one digital sweep) the 7854 will not recognize
it, and the system will keep on digitizing.
When the 7854 is used for non-single-sweep acquisition
(AQR), the 7B87 clock should be disabled by selecting the
EXT/AQR pushbutton and rernoving any connection from
the EXT CLOCK IN connector. This prevents the 7B87
clock signal from interfering with the 7854 acquisition
mode.
To obtain a stored single-sweep display of a repetitive
signal with a 7854 digitizing oscilloscope, first obtain a
real-time display (7854 set to Scope CRT Display Mode)
in the NORM TRIGGERING MODE. Then select the
portion of pretrigger and post-trigger desired for the
subsequent stored single-sweep display with the
ACQUIRE-STOP DELAY control. The displayed intensified
zone relates to the portion of the single-sweep displayed
after the single-sweep trigger event (post-trigger) and the
non-intensified zone relates to the portion of single-
sweep displayed before the single-sweep trigger event
REV A MAR 1981

occurs (pretrigger—see Fig. 1-3). The exact amount of the
post-trigger display is indicated by the CRT readout.
Then, without changing other triggering controls, select
the single-sweep mode by pressing the SINGLE SWP.
RESET pushbutton. Set the 7854 to the Stored CRT
Display mode and to the AQS (acquire single-shot) WFM
Acquisition mode. When the AOS button is presed, the
7854 will respond by lighting the “Busy” LED and
blanking the entire screen. Arm the single-sweep
function by pressing the SINGLE SWP RESET pushbutton
again. After the trigger event occurs, the stored
waveform will be displayed on screen. A single stored
trace is displayed each time the 7854 AOS function is
selected and the 7B87 SINGLE SWP RESET pushbutton
is pressed.
\f an Error message is displayed at the bottom of the CRT,
the 7B87 clock is running faster than the 7854 can
digitize, and the single sweep will not be acquired. To
remedy this error condition, select a slower TIME/DIV
setting and re-acquire the single-sweep display until the
Error message disappears and the single-sweep display
is stored. If the 7854 does not return from the “Busy”
state or if it is desired to abort the AQS before the trigger
event has occurred, press Stop Ext Acquire button on the
7854 rear panel.
TRIGGER COUPLING
The TRIGGERING COUPLING pushbuttons select the
method in which the trigger signal is connected to the
trigger circuits. Each position permits selection or
rejection of some frequency components of the signal
which triggers the sweep.
AC. AC COUPLING blocks the de component of the
trigger 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 a low repetition rate or a
dc level, one of the other COUPLING switch positions will
provide a better display.
REV A MAR 1981
Operating Instructions--7B87
AC LF REJ. AC LF REJ COUPLING rejects dc, and
attenuates low-frequency trigger signals below about 30
kilohertz. 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 trigger signal contains line-frequency
components. Also, the AC LF REJ position provides the
best alternate-mode vertical 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. De is rejected and signals outside the above
range are attenuated. When triggering from complex
waveforms, this position is useful to provide a stable
display of the low-frequency components.
DC. DC COUPLING can be used to provide stable
triggering from low-frequency signals which would be
attenuated in other COUPLING switch positions. DC
COUPLING can be used to trigger the sweep when the
trigger signal reaches a dc 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 pushbuttons select the
source of the trigger signal which is connected to the
trigger circuits.
INTERNAL. The INT position causes the 7B87 to trigger
on the trigger signal from the vertical plug-in unit.
Further selection of the internal 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 applications, the internal
source can be used. However, some applications require
special triggering which cannot be obtained in the INT
position. In such cases, the LINE or EXT positions of the
SOURCE switches must be used.

Operating Instructions-—7B87
ost
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(LEVEL) W
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emia
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TIM
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Figure 1-4. Effect of LEVEL contro! and SLOPE switch on crt display.
1-10 REV A MAR 1981