Tektronix 7B85 User manual

Tektronix, Inc.
P.O.
Box 500
Beaverton, Oregon 97077
070-1961-01
Product Group 42
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7885
DELAYING
TIME BASE
WITH OPTIONS
INSTRUCTION MANUAL
Serial Number -------
First Printing JAN 1976
Revised AUG 1983

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Copyright 1976, 1981 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 panel 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:
BOOOOOO
100000
200000
300000
700000
Tektronix, Inc., Beaverton, Oregon, USA
Tektronix Guernsey, Ltd., Channel Islands
Tektronix United Kingdom, Ltd., London
Sony/Tektronix, Japan
Tektronix Holland, NV, Heerenveen,
The Netherlands

7885 Instruction
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS. . . . . . . . . . . . . . . . .. iv
LIST OF TABLES .......................... v
SAFETY SUMMARY. . . . . . . . . . . . . . . . . . . . . .. vii
Section 1 OPERATING INSTRUCTIONS
REV AUG 1981
Features . . . . . . . . . . . . . . . . . . . . . . . 1-1
Installation ..................... 1-1
Controls, Connectors,
and Indicators
................... 1-1
Functional Check ................ 1-1
Setup Procedure . . . . . . . . . . . . . . 1-4
Sweep Functions. . . . . . . . . . . . . . 1-4
Normal Sweep . . . . . . . . . . . . . 1-4
Magnified Sweep
........... 1-4
Delaying and Delayed Sweep .. 1-4
6. (Differential) TIME ......... 1-5
Triggering Functions
........... 1-5
General Operating Information ...... 1-6
Triggering Switch Logic ......... 1-6
Triggering Modes .............. 1-6
P-P AUTO ................... 1-6
AUTO ....................... 1-6
NORMal ..................... 1-6
SINGLE SWeeP ............... 1-6
Trigger Coupling ............... 1-7
AC ....................... 1-7
AC LF REJ ................ 1-7
AC HF REJ ................ 1-7
DC ....................... 1-7
Trigger Source
................ 1-7
INTernal ................... 1-7
LINE
..................... 1-7
EXTernal .................. 1-7
Trigger
Slope. . . . . . . . . . . . . . . . . 1-8
Trigger Level . . . . . . . . . . . . . . . . . 1-8
Horizontal Sweep Rates ........ 1-8
Time Measurement
............ 1-8
Sweep Magnification
........... 1-8
Variable Hold Off .............. 1-8
Delay-Time Operation . . . . . . . . . . 1-8
6. TIME Operation ............. 1-11
6. TIME Operation in a
Dual-Beam Oscilloscope
Mainframe ................. 1-11
Mainframe Operating Modes ..... 1-11
Page
Applications. . . . . . . . . . . . . . . . . . . . . . . 1-13
Delayed-Sweep Measurements . . . . . 1-13
Time-Interval Measurements
(Delay-Time Mode) ............. 1-13
Differential Time-Interval
Measurements (6. Time Mode) ... 1-14
Delayed-Sweep Magnification .... 1-14
Triggered Delayed-Sweep Magnifi-
cation. . . . . . . . . . . . . . . . . . . . . . . 1-18
Independent Time-Interval
Measurements . . . . . . . . . . . . . . . . . . 1-18
Section 2 SPECIFICATION
Standard Accessories ............... 2-4
WARNING I
THE REMAINING PORTION OF THIS TABLE OF
CONTENTS LIST 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 QUALI-
FIED
TO DO So.
Section 3 THEORY OF OPERATION
Block Diagram Description . . . . . . . . . . . 3-1
Trigger Generator
................ 3-1
Sweep Generator ................ 3-1
Pickoff Amplifiers and Delay
Gate Generator. . . . . . . . . . . . . . . . . . 3-1
Logic
.......................... 3-1
Digital Voltmeter. . . . . . . . . . . . . . . . . 3-1
Detailed Circuit Description ........... 3-3
Logic Fundamentals
.............. 3-3
Non-Digital Devices . . . . . . . . . . . . . . 3-3
Front-Panel Distribution ........... 3-6

7885 Instruction
TABLE OF CONTENTS (cont)
Page
Section 3 THEORY OF OPERATION (cont)
ii
Trigger Generator ................ 3-6
External
Source. . . . . . . . . . . . . . . 3-6
Internal and Line Source ........ 3-6
Trigger Source Selector and
Amplifier. . . . . . . . . . . . . . . . . . . . . 3-6
Peak-to-Peak
Auto ............ 3-8
Slope Selector and Trigger
Generator. . . . . . . . . . . . . . . . . . . . 3-8
Gate Generator . . . . . . . . . . . . . . . 3-9
Logic
.......................... 3-10
Sweep Modes . . . . . . . . . . . . . . . . 3-10
Hold
Off Timing . . . . . . . . . . . . . . . 3-11
Lockout Buffer Amplifier . . . . . . . . 3-11
Hold
Off Generator . . . . . . . . . . . . 3- 11
Hold Off Output Amplifier . . . . . . . 3-11
Delay Pickoff Inhibit.
........... 3-12
Delay
Mode Control. . . . . . . . . . . . 3-12
Auxiliary Y-Axis Generator . . . . . . 3-12
Sweep Generator. . . . . . . . . . . . . . . . 3-13
Timing Current Source. . . . . . . . . . 3-13
Ramp Generator . . . . . . . . . . . . . . 3-13
Output Preamplifier . . . . . . . . . . . . 3-13
Sweep Gate Generator . . . . . . . . . 3-16
Pickoff Amplifiers and Delay
Gate Generator. . . . . . . . . . . . . . . . . . 3-16
Delay Time Comparison
(SI\! B088750 & Up) ............ 3-16
Delay Time Comparison
(SN B088749 & Below) ......... 3-16
~ Time Comparison
(SN B088750 & Up) ............ 3-16
~ Time Comparison
(SN B088749 & Below) ......... 3-18
Delay Bias and Second Delay
Pickoff Clamp
................. 3-18
Delay Comparison Voltage
Switch . . . . . . . . . . . . . . . . . . . . . . 3-18
Delay Gate Generator . . . . . . . . . . 3-18
~Symbol Enable ............... 3-19
Digital Voltmeter
................. 3-19
Delay Comparison Voltage
to Ramp
Converter (SN B088750 & Up)
... 3-20
Delay Comparison Voltage
to Ramp
Converter (SN B088749 & Below) 3-21
Page
Comparator (SN B088750 & Up) . 3-21
Comparator (SN B088749 &
Below)
...................... 3-21
Ramp Control
................ 3-21
Divide by 4 Counter
............ 3-21
Timer
....................... 3-21
Reference Current Source
(SN B088750 & Up) ............ 3-22
Reference Current Source
(SN B088749 & Below) ......... 3-22
Reference Current Inverter
(SN B088750 & Up)
............ 3-22
Reference Current Inverter
(SN B088749 & Below)
......... 3-22
Reference Current
Switch. . . . . . . 3-22
Counter and Encoder
(SN B088750 & Up) ............ 3-22
Counter and Encoder
(SN B088749 & Below) ......... 3-22
Counter Transfer Control.
....... 3-23
Zero Count Correction .......... 3-23
Time/Division and Readout
Switching . . . . . . . . . . . . . . . . . . . . . . 3-23
Basic Readout System . . . . . . . . . 3-23
Time/Division and Readout . . . . . . 3-23
Delay Time Readout
........... 3-23
Interface Connectors and Power
Supply. . . . . . . . . . . . . . . . . . . . . . . . . 3-24
Section 4 MAINTENANCE
Preventive Maintenance ............. 4-1
Cleaning . . . . . . . . . . . . . . . . . . . . . . . 4-1
Exterior . . . . . . . . . . . . . . . . . . . . . 4-1
Interior ...................... 4-1
Switch Contacts . . . . . . . . . . . . . . 4-1
Visual Inspection ................ 4-1
Lubrication . . . . . . . . . . . . . . . . . . . . . 4-2
Cam Switch Lubrication
......... 4-2
Semiconductor Checks. . . . . . . . . . . . 4-2
Adjustment After Repair
........... 4-2
Troubleshooting
................. 4-3
REV AUG 1981

7B85 Instruction
TABLE OF CONTENTS (CONT.)
Page
Section 4 MAINTENANCE (cont)
Troubleshooting Aids . . . . . . . . . . . . . 4-3
Diagrams . . . . . . . . . . . . . . . . . . . . 4-3
Voltages and Waveforms. . . . . . . . 4-3
Circuit-Board Illustrations
....... 4-3
Switch Cam Identification ....... 4-3
Diode Color Code . . . . . . . . . . . . . 4-3
Wiring Color
Code. . . . . . . . . . . . . 4-3
Semiconductor Basing. . . . . . . . . . 4-3
Inter-Board Pin Connector
Identification. . . . . . . . . . . . . . . . . . 4-3
Multi-Pin Connector Identification. 4-3
Interface Connector Pin Locations 4-3
Performance Check and
Adjustment.
.................. 4-5
Troubleshooting Equipment
........ 4-5
Troubleshooting Techniques
........ 4-6
Troubleshooting Procedure
...... 4-6
Corrective Maintenance
............. 4-10
REV AUG 1981
Obtaining Replacement Parts ....... 4-10
Soldering Techniques
............. 4-10
Component Removal and
Replacement. . . . . . . . . . . . . . . . . . . . 4-11
Circuit Boards . . . . . . . . . . . . . . . . 4-
11
Switches .... . . . . . . . . . . . . . . . . 4-14
Semiconductors. . . . . . . . . . . . . . . 4-14
Interconnecting Pins
........... 4-14
Circuit-Board Pins
............. 4-15
Front-Panel Lights ............. 4-15
Adjustment After Repair
........... 4-15
Instrument Repackaging .......... 4-15
Page
Section 5 PERFORMANCE CHECK AND
ADJUSTMENT
Preliminary Information ............ 5-1
Adjustment Interval ............ 5-1
Tektronix Field Service .......... 5-1
Using This Procedure .......... 5-1
Test Equipment Required .......... 5-1
Special Fixtures. . . . . . . . . . . . . . . 5-1
Test Equipment Alternatives ..... 5-1
Index to Performance Check
and Adjustment Procedure. . . . . . . . . 5-4
Preliminary Procedure . . . . . . . . . . . . 5-4
A. Triggering System ............. 5-5
B. Horizontal System ............. 5-10
Section 6 INSTRUMENT OPTIONS
Section 7 REPLACEABLE ELECTRICAL PARTS
Section 8 DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
Section 9 REPLACEABLE MECHANICAL PARTS
CHANGE INFORMATION
iii

7885 Instruction
LIST OF ILLUSTRATIONS
Fig.
No.
1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
1-9
1-10
1-11
1-12
2-1
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
iv
Page
7B85 Delaying Time Base. . . . . . . . . . . . . . viii
Location of release latch. . . . . . . . . . . . .
.. 1-1
Front-panel controls, connectors,
and indicators . . . . . . . . . . . . . . . . . . . . .
.. 1-2
Effects of LEVEL control and SLOPE
switch on crt display ................. .
Area
of graticule used for most accurate
time measurements
.................. .
Effect of sweep magnifier on crt display
.. .
(A) Delaying-sweep display produced by
7B85
in the A horizontal compartment. (B)
Delayed-sweep display produced by com-
panion time-base unit
in the B horizontal
compartment
....................... .
Typical
t, (differential) time operation .... .
Measuring time intervals from a triggering
event (start of sweep)
to any point on a
waveform
.......................... .
Measuring rise time, fall time, period, fre-
quency, or pulse width
in the ~ (differential)
time mode
......................... .
Magnifying a selected segment of the delay-
ing (A) sweep
in the delay-time mode with
mainframe alternate
or chopped horizontal
operation
.......................... .
Time-interval measurements
in the delay-
time and
t, (differential) time mode with
mainframe alternate or chopped operation.
Examining
an event that occurs within a se-
lected time interval after a known delay time
in the delay-time mode ............... .
7B85 dimensional drawing
............ .
Basic block diagram of the 7B85 Delaying
Time-Base unit
..................... .
Detailed block diagram of Trigger Generator
Functional diagram
of Trigger Source Selec-
tor
............................... .
Timing diagram for Gate Generator stage
(092, 096, 098) .................... .
Detailed block diagram of Logic circuit ... .
Timing diagram for Delay Pickoff Inhibit
stage ............................. .
Detailed block diagram
of Sweep Generator
Detailed block diagram of Pickoff Amplifiers
and Delay Gate Generator
............ .
1-9
1-10
1-10
1-10
1-12
1-14
1-15
1-16
1-17
1-18
2-4
3-2
3-7
3-8
3-9
3-10
3-12
3-14
3-17
Page
3-9 Digital Voltmeter detailed block diagram
(SN B088749 & below) . . . . . . . . . . . . . .
.. 3-19
3-10
4-1
Digital Voltmeter timing diagram. . . . . . . .. 3-20
Lubrication procedure for a typical cam
switch. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4-2
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
Semiconductor lead configuration
....... .
Inter-board multi-pin connector assembly ..
End-lead multi-pin connector assembly ...
Location of pin numbers on Interface con-
nector
............................ .
7B85 troubleshooting chart.
........... .
Readout board removal procedure
...... .
Coaxial end-lead connector assembly
... .
Cam switch removal procedure
........ .
Removal procedure for typical push-button
switch
............................ .
Exploded view
of circuit-board pin and ferrule
Front-panel light socket assembly
...... .
4-4
4-5
4-5
4-6
4-8
4-12
4-13
4-16
4-18
4-19
4-19
The illustrations
in Section 8 are located near their
associated diagram
on the foldout pages.
8-1 Semiconductor lead configuration.
8-2 Location
of circuit boards in the 7B85.
8-3 A
1-lnterface circuit board assembly.
8-4
A2- Trigger circuit board assembly.
8-5
A3-Readout circuit board assembly.
8-6A
A4-(SN B088750 & Up) Digital Voltmeter cir-
cuit board assembly.
8-6B
A4-(SN B088749 & Below) Digital Voltmeter
circuit board assembly.
8-7 A
1-lnterface circuit board assembly.
8-8
A2- Trigger circuit board assembly.
8-9A
A4--(SN B088750 & Up) Digital Voltmeter cir-
cuit board assembly.
8-9B
A4-(SN B088749 & Below) Digital Voltmeter
circuit board assembly.
8-10 Readout circuit board assembly.
8-11 Location of Sweep Timing adjustments.
8-12 Location
of Triggering adjustments.
8-13A (SN B088750 & Up) Location of Digital
Voltmeter adjustments.
8-13B (SN B088749 & Below) Location of Digital
Voltmeter adjustments.
REV AUG 1981

REV AUG 1981
Table
No.
2-1
2-2
2-3
3-1
3-2
4-1
5-1
5-2
5-3
5-4
5-5
LIST OF TABLES
Electrical Characteristics .............. .
Environmental Characteristics
.......... .
Physical Characteristics .............. .
Basic Logic Reference "
............. .
Readout Character Selection
.......... .
Shipping Carton Test Strength
......... .
Test Equipment
..................... .
Delay Time Readout Bias ............. .
~ Time Accuracy .................... .
Sweep Timing
...................... .
Magnified Sweep Timing
.............. .
Page
2-1
2-4
2-4
3-4
3-24
4-19
5-2
5-12
5-16
5-18
5-19
7B85 Instruction
v

7885 Instruction
SAFETY SUMMARY
This manual contains safety information 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.
Ground the Instrument
To reduce electrical-shock hazard, the mainframe (oscilloscope) chassis must be properlygrounded. Refer to the
mainframe manual for grounding information.
Do Not Operate in Explosive Atmospheres
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 internal adjustments to this instrument unless anotherperson, capable of giving first aid
andresuscitation, is present.
WARNING I
Warning Statements
Warning statements accompany potentially dangerous procedures in this manual. The following warnings appear
in this manual andare 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. A
vOid getting silicone grease in eyes. Wash hands thoroughly after use.
REV AUG 1981
vii

7885 Instruction
TIIIC "O
TRIGGERING
LEVel •
?'"'~
.oo,
tOUI't.lHC SOIlJICl
p., 101110
"
'"
II
• •
.. tl TO
..t LlII( J
U"'
,
Iii
..
Iii
,
.. ,,'
"'"
At Kf IU
'"
,
fi NE •
Ii
II Iii
,
POSITION
t" ri'
"
,
iii
HOLD
OFF
,
lI(Sn
,
MAG
,-
, B
DELA Y MODE
I fIj XI
,
II
IIID(Pl IOEIJT
IiiiT ---;w- \' A
, I S'AIITS
,
A'TtIl OlY
, •
TIIIGGEIlAIU , -
,
Amll on
,
DElAY TIME
,
,
,
,
• 6
TIME
TRACE SEP
-,
•
...!!.!.!J '
0111 +10 •
•
• •
•
•
e-
s ••
•
'"
1~
TEKTRONIX .
•
DELAYING
TIME BASE
7885
1961 ·a OA
7B85 D elaying Time Base
viii
RE V AUG 1981

Section 1-7885
OPERATING INSTRUCTIONS
The 7B85 Delaying 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.
FEATURES
The 7B85 Delaying Time Base unit provides calibrated
sweep rates from 5 s to 10 ns and triggering to 400 MHz for
7700-, 7800-, and 7900-Series oscilloscopes. The X1 0 Mag-
nifier increases each sweep rate by a factor
of 10 and the
VARIABLE control allows continuously variable sweep rates
between calibrated steps. Variable hold off and alphanumer-
ic readout are provided. Also, when operating in the AUTO
TRIGGERING MODE, a bright baseline trace is displayed
in
the absence of a trigger signal.
INSTALLATION
The time-base unit is designed to operate in the horizon-
tal plug-in 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 specifi-
cations given
in Section 2.
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 stan-
dardized, 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, pull the release latch (see Fig. 1-1)
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 pan-
REV AUG 1981
TRIGGERING
C1960-13
Fig. 1-1. Location of release latch.
el. Figure 1-2 provides a brief description of all front-panel
controls, connectors,
and indicators. More detailed informa-
tion
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
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.
1-1
-------"" -----

Operating Instructions-7B85
SWEEP MODE
DELAY TIME
1-2
rFiI B STARTS
IY AFTER DlY
rFiI B TRIGGERABlE
IY AFTER DlY
TRIGGERING
I I
MODE COUPLING
P-P AUTO AC
C o;!.u
7
SOURCE
INT
[J)
AUTO AC IF REJ LINE
Fig. 1-2. Front-panel controls, connectors, and indicators.
TRIGGERING
EXTERNAL
TRIGGER
INPUT
REV AUG 1981

Operating Instructions-7B85
TRIGGERING
G) LEVEL Control-Selects a point on the trigger signal where triggering occurs.
eD SLOPE Switch-Permits sweep to be triggered on negative· or positive·going portions of the trigger signal.
CD READY Indicator-Illuminates when sweep circuit is armed (SINGLE SWEEP Model.
o TRIG'D Indicator-Illuminates when the display is triggered.
CD MODE Push buttons-Selects the operating mode of the triggering circuits.
® COUPLING Pushbuttons-Selects the method of coupling the trigger signal to triggering circuit.
(j) SOURCE Push buttons-Selects source of the trigger signal.
CD
®
@
®
@
@
@
SWEEP
POSITION Control-Provides horizontal positioning.
FINE Control-Provides precise horizontal positioning.
HOLD OFF Control-Permits hold off period to be varied to improve triggering stability of repetitive complex waveforms.
MAG
Pushbutton-Selects X10 magnified or unmagnified sweep.
TIME/DIV Switch-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 in which
the 7B85 may be used.
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.
®
@
SWEEP MODE
B DELAY MODE Pushbuttons-Selects independent or delaying sweep operation. In the B STARTS AFTER DLY and
B TRIGGERABLE AFTER DLY delaying sweep modes, the DELAY TIME and ~ TIME functions are activated. There
will be a 2 division vertical shift of the trace when switching from INDEPENDENT to B STARTS AFTER DELAY.
DELAY TIME
DELAY TIME Control-Provides variable delay time before the start of the delayed sweep produced by companion time-
base unit.
® TRACE SEP Control and Switch-Enables lo TIME functions and provides vertical separation of the delayed sweep
traces (lo TIME operation).
@
OloTIMEControl-providesdifferentialtime measurements between 2 selected intensified zones on the delaying sweep
trace. Two delayed sweep traces corresponding to the intensified zones are displayed by the companion time-base unit.
Differential time is displayed on the crt readout.
1960·14
Fig. 1-2. Front-panel controls, connectors, and indicators (cont.).
REV AUG 1981
1-3

Operating Instructions-7B85
Setup Procedure
1. Install the 7B85 in the A horizontal compartment of
the mainframe.
2. Install an amplifier plug-in unit in a vertical
compartment.
3. Set the 7B85 controls as follows:
SLOPE
(+)
MODE P-P AUTO
COUPLING AC
SOURCE INT
B DELAY MODE INDEPENDENT
TRACE SEP OFF (fully clockwise)
POSITION Midrange
TIME/DIV 1 ms
VARIABLE (CAL IN) Calibrated (Pushed in)
HOLD OFF MIN (fully counter-
clockwise)
MAG
X1 (pushed in)
4. Turn on the oscilloscope 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 ob-
tain a normal sweep and to demonstrate the function
of the
related controls.
1. Perform the preceding Setup Procedure.
2. Connect a 0.4 V, 1 kHz 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.
1-4
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 cen-
ter 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) control fully counterclockwise
and note that the displayed sweep rate changes to at least
the next slower TIME/DIV switch setting (i.e., 2 ms/div).
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 func-
tion 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 (X1 0). Note that the
unmagnified display within the center division
of the
graticule is magnified to about 10 divisions.
3. Press the MAG button (X1).
Delaying and Delayed Sweep. Perform the following
procedure to obtian delaying- and delayed-sweep displays
and to demonstrate the function of the related controls. To
obtain a delayed-sweep display, a companion time-base unit
must
be installed in the B horizontal compartment of the
mainframe.
1. Obtain a display as described in the preceding Normal
Sweep procedure.
2. Press the B STARTS AFTER DLY button.
3. Set the mainframe horizontal mode for chopped
operation.
4. Set the companion time-base unit sweep rate for
0.1 ms/div, and triggering for p-p auto mode, ac coupling,
internal source, and + slope.
REV AUG 1981

5. Adjust the mainframe 8 sweep intensity and check for
an intensified zone about 1 division wide on the delaying (A)
sweep display. Also note that the delayed (8) sweep pro-
vides
an expanded display of the intensified portion of the
delaying (A) sweep.
6. Position the start of the delaying (A) sweep to the left
edge of the graticule.
7. Adjust the DELAY TIME control for a crt readout (bot-
tom division of crt graticule) of 5.000 ms. Check that the left
edge of the intensified zone is at the graticule center line.
8. Set the 7885 TIME/DIV switch to .5 ms and the de-
layed (8) sweep unit sweep rate to 20 j.Ls/div.
9. turn the DELAY TIME control fully counterclockwise
to position the intensifed zone near the front corner
of the
first square-wave cycle. Press the 8 TRIGGERA8LE
AFTER DLY button and check that the intensifed zone
moves to the front corner of the next displayed square
wave.
~ (Differential) TIME. Perform the following procedure
to obtain a
~ (differential) time display and to demonstrate
the function
of the related controls.
1. Obtain a delaying (A) and delayed (8) sweep display
as described in steps 1 through 4 of the preceding Delaying
and Delayed Sweep procedure.
2. Turn the TRACE SEP control counterclockwise out of
the OFF (detent) position.
3. Set the DELAY TIME and ~ TIME controls to the fully
counterclockwise position. Check for two delayed (8)
sweeps and note that the crt readout (bottom right
of crt) is
0.000 ms.
4. Slowly turn the ~ TIME control clockwise and note
that a second intensified zone moves across the delaying
(A) sweep display, and the crt readout indicates the differen-
tial time between the left edge of the stationary intensified
zone and the left edge
of the second intensified zone. Also
note that the lowel" delayed (8) sweep is an expanded dis-
play of the second intensified zone.
Triggering Functions
Perform the following procedure to obtain a triggered
sweep and to demonstrate the functions
of the related
controls.
REV AUG 1981
Operating Instructions-7B8S
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 posi-
tions of the HOLD OFF control. Return the HOLD OFF con-
trol to the fully counterclockwise (MIN) position.
NOTE
The HOLD OFFcontrol varies the sweep holdofftime,
which effectively changes the repetition rate
of the
horizontalsweep signal. However, its primary function
is to obtain a stable display
of complex waveforms
that are otherwise difficult to trigger.
4. Press the AC, AC HF REJ, and DC COUPLING but-
tons for both the + and -positions
of the SLOPE switch
and check for a stable display (LEVEL control may
be
adjusted, if recessary, to obtain a stable display).
5. Apply the 0.4 V, 1 kHz signal from the mainframe cali-
brator to the ampifier 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 but-
tons 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.
1-5

Operating Instructions-7B85
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
connected 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 a sequence that
places the most-often used position at the top of each se-
ries of push buttons. With this arrangement, a stable 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
TRIG'D light is not on, the LEVEL control is either at a set-
ting 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 selec-
tions 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 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 trig-
gers at the same percentage point
on the leading edge of a
high-amplitude signal if the LEVEL control
is not changed.
1-6
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 baseline, reference
trace (TRIG'D light off). When
an adequate trigger signal is
again applied, the free-running condition ends and a trig-
gered display
is presented.
The
P-P AUTO MODE is particularly useful when observ-
ing 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 ease of
obtaining a triggered display. The AUTO, NORM, and SIN-
GLE 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 sig-
nal 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 trig-
gered displays with trigger repetition rates below approxi-
mately 30
Hz. When the TRIG'D light is off, no trace is
displayed.
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 presenta-
tion. Under these circumstances, a stable display can often
be obtained by using the single-sweep feature of this unit.
REV AUG 1981

The single-sweep mode is also useful to photograph non-
repetitive or unstable displays.
To obtian 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 displayed 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
persistence, 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 recom-
mended
in the mainframe instruction manual.
When using the single-sweep mode to photograph
waveforms, the graticule may have to
be photographed sep-
arately, 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 but-
ton only once for each waveform unless the signal is com-
pletely symmetrical. Otherwise, multiple waveforms 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 TRIGGER COUPLING push buttons select the meth-
od
in which the trigger signal is connected to the trigger
circuits.
Each position permits selection or rejection of some
frequency components of the signal that triggers the sweep.
AC.
AC COUPLING blocks the dc component of the trig-
ger signal. Signals with low-frequency components below
approximately 30
Hz are attenuated. In general, AC COU-
PLING 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 dc level,
one of the other COUPLING switch positions will provide a
better display.
AC LF REJ. AC LF REJ COUPLING rejects dc, and at-
tenuates low-frequency trigger signals below approximately
30 kHz. Therefore, the sweep is triggered only by the high-
er-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
REV AUG
1981
Operating Instructions-7B85
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 alilow-fre-
quency signals between approximately 30 Hz and 50 kHz.
Dc is rejected, and signals outside the above range are at-
tenuated. 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 trig-
gering from low-frequency signals that 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 af-
fects the triggering point.
Trigger Source
The TRIGGERING SOURCE push buttons select the
source
of the trigger signal connected to the trigger circuits.
INTernal. The INT position connects 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 in-
struments for more information. For most applications, the
internal source can be used. However, some applications
require special triggering that cannot be obtained in the INT
position. In such cases, the LINE or EXT positions of the
SOURCE switches must be used.
LINE. The LINE position connects a sample of the pow-
er-line voltage from the mainframe to the trigger circuit. Line
triggering is useful when the input signal is time-related (mul-
tiple or submultiple) to the line frequency. It is also useful for
providing a stable display
of a line-frequency component in a
complex waveform.
EXTernal. The EXT position connects the signal from the
EXT TRIG
IN connector to the trigger circuit. The external
signal must
be time-related to the displayed waveform for a
stable display. An external trigger signal can be used to pro-
vide a triggered display when the internal signal
is either too
low in amplitude for correct triggering or contains signal
components on which triggering is not desired. It is also
useful when signal tracing
in amplifiers, phase-shift net-
works, wave-shaping circuits, etc. The signal from a single
point in the circuit can be connected to the EXT TRIG IN
connector through a probe or cable. The sweep is then trig-
gered by the same signal at
all times and allows amplitude,
time relationship, or waveshape changes of signals at var-
1-7
--- ------- -- ----

Operating Instructions-7BSS
ious pOints in the circuit to be examined without resetting
the TRIGGERING controls.
The -;- 10 push buttons attenuates the external trigger
signal by a factor of 10. Attenuation of high amplitude exter-
nal 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 trig-
ger circuit responds on the positive- or negative-going por-
tion
of the trigger signal. When the SLOPE switch is in the
(+)(positive-going) position, the display starts on the posi-
tive-going portion of the waveform (see
Fig. 1-3). When sev-
eral cycles of a signal appear in the display, the setting of
the SLOPE switch is often unimportant. However, if only a
certain portion
of a cycle is to be displayed, correct setting
of the SLOPE switch is important to provide a display that
starts on the desired slope of the input switch.
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 a more positive point on the trigger sig-
nal. When the LEVEL control is set in the -region, the
trigger circuit responds at a more negative point on the trig-
ger 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 clockwise
until the display starts at the desired point. Less selection
of
the triggering level is available as the trigger signal frequen-
cy exceeds 150 MHz.
Horizontal Sweep Rates
The TIME/DIV switch provides calibrated sweep rates
from 5 s/div to 10 ns/div
in a 1-2-5 sequence. The VARI-
ABLE TIME/DIV control must be in the calibrated position
and the MAG switch set to
X1 to obtain the sweep rate
indicated by the TIME/DIV switch. However, the mainframe
crt readout will display the appropriate sweep rate.
The VARIABLE TIME/DIV control includes a two-
position switch to determine if the sweep rate is calibrated,
or uncalibrated. 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 ac-
tivated for uncalibrated sweep rates, to at least the sweep
rate of the next slower position.
1-8
A calibrated 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 a specific
uncalibrated sweep rate has been obtained
and it is desired
to switch between calibrated and uncalibrated displays.
Time Measurements
When making time measurements from the graticule, the
area between the second
and tenth vertical lines of the
graticule provides the most linear time measurements (see
Fig. 1-4). Position the start of the timing area to the second
vertical ine 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
Fig. 1-5). The equivalent length of the magnified sweep
is more than 100 div; any 10-div 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 equiv-
alent 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
repetitive 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 a stable display cannot
be obtained with the TRIG-
GERING LEVEL control, the HOLD OFF control can
be var-
ied for an improved display. If a stable display cannot be
obtained at any setting of the LEVEL and HOLD OFF con-
trols, check the TRIGGERING COUPLING and SOURCE
switch settings.
Delay-Time Operation
A 7B85 installed in the mainframe A horizontal compart-
ment can delay a companion time-base unit installed
in the
B horizontal compartment. When operating the 7B85
in a
delaying mode (B DELAY MODE switch set to B STARTS
AFTER DLY or B TRIGGERABLE AFTER DLY), an intensi-
fied zone is provided on the delaying sweep display during
the time that the companion time-base unit runs (see
Fig.
1-6). A delayed-sweep trace is provided by the companion
time-base unit, corresponding to the intensifed zone
on the
delaying trace, at the sweep rate set by the TIME/DIV
REV AUG 1981

TRIIi'O
~Ib@i?~ •
LEVEL
-/ •.... ,.
f~ ~, ••••
(LEVELI~ (SLOPEI
CRT DISPLAY
OBTAINED WITH
SLOPE SWITCH
SET TO POSITIVE (+)
CRT DISPLAY
OBTAINED WITH
SLOPE SWITCH
SET TO NEGATIVE (-)
TRIIi'O
~Ib@i?~ •
LEVEL
U·~
~
TRIG'O
<Ollb@i?lli.
LEVEL
~a~
©J
TRIG'O
®Ib(i)ii?lli •
LEVEL
~D~
~
••••
••••
•••
f--
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l~
f--
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-
7
\
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,
\
Operating Instructions-7B85
I I I
POSITIVE
SLOPE (+)
1.1
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rf\
[\ {
1(\
[\
V \ \
1\
\ \
1\
1\ r\
I \
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IV
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POSITIVE
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17
1\ ~ 7'
If\. ~
\ I \ I \ \
\ I \ I
1\
1 \
1\1 .I W
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NEGATIVE
/SLOPE (-)
7
7\ \ f
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NEGATIVE
SLOPE (-)
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C1960-30
Fig. 1·3. Effects of LEVEL control and SLOPE switch on crt display.
REV AUG 1981
1-9

Operating Instructions-7B85
SECOND-VERTICAL
LINE
I
TENTH-VERTICAL
LINE
1
,
~
++-++
I I
1 ...... ----- TIME MEASUREMENT --".~I
AREA
C1752-06
Fig. 1-4. Area of graticule used for most accurate time
(A)
500 mV
"'"""
,
500
1
mV/
/
1
1 r
1
1
/
/
/
/
/
/
/
INTENSIFIED
PORTION
\ 1
ms
\
,..~
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/ \
/ \,\
5_612 ms\
1 ms
\ \ \ \
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100 J.1s
\ \
-
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1
1
1
1
measurements. (6)
1
1 ms
~
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r-
--h r-
r-
- --
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UNMAGNIFIED 01
SPLAY
\ \
-
,~
--
\
I \
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MAG-Xl
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I I I.'
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MAGNIFIED DISP
LAY
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1 I I
1960-16
Fig. 1-5. Effect of sweep magnifier on crt display_
1-10
1 1
L f
'-rl
5.612 ms
1960-17
Fig. 1-6. (A) Delaying-sweep display produced by 7885 in the
A horizontal compartment. (8) Delayed-sweep display pro-
duced by companion time-base unit in the 8 horizontal
compartment.
switch of the companion time-base unit (see Fig. 1-6). The
delay time between the triggering event that starts the de-
laying-sweep trace and the start of the intensified zone (and
corresponding delayed sweep),
is determined by the 7885
TIME/DIV switch and DELAY TIME control. The amount of
calibrated delay time
is displayed on the crt readout.
To view the delaying-sweep trace (intensifed display), set
the mainframe horizontal mode switch to
A; to view the cor-
responding delayed-sweep trace, set the mainframe hori-
zontal mode switch to 8. To view the delaying trace
(intensifed) and the corresponding delayed-sweep trace
on
the same display, set the mainframe horizontal mode switch
to alternate or chop.
Triggering for the delaying-sweep trace is controlled by
the
7885 TRIGGERING controls. Triggering for the intensi-
fied zone on the delaying-sweep trace and the correspond-
REV AUG
1981