Tektronix 7B85 User manual

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M A N I~ .1
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Tektronix, Inc .
P .O . Box 500
Beaverton, Oregon

97077

Serial Number
_
COMMITTED
TO EXCELLENCE
Al"IQN
070-1961-01

First Printing JAN 1976
Product Group 42

Revised AUG
1983

7885 Instruction
LISA" OF ILLUSTRATIONS
. . ............. . . .

iv

Applications . . ............. ..... ... 1-13
LIST OF TA~LI~S
......... . ............. . . . v

Delayed-Sweep Measurements ..... 1-13
SAF T"Y SUMMARY ....... . . ..............

vii

Time-Interval Measurements
(Delay-Time Mode) ..... . . . . .... 1-13
Section 1 OPEi~A"i - ING INSTFtUC~'IONS

Differential Time-Interval
Features ......... . ............. 1-1

Measurements (~ Time Mode) ... 1-14
Installation ....... . ............. 1-1

Delayed-Sweep Magnification ....
1-14
Controls, Connectors,

T°riggered Delayed-Sweep
Magnifi-
and Indicators ..... . . ............ 1-1

cation ............... . . ...... 1-18
Functional Check ... . . ........... 1-1

Independent Mime-Interval
Setup Procedure . . . ........... 1~4

Measurements .......... . . . . .... 1-18
Sweep Functions . . . . . ......... 1-4
Normal Sweep . . . . . ........ 1-4
Magnified Sweep . . . ........ 1-4

SeCtiOn 2
SPECIFICATION
Delaying and Delayed Sweep . . 1-4
~ (Differential) TIME . ........ 1-5

Standard Accessories ............ . . . 2-4
Triggering Functions ... . ....... 1-5
General Operating Information ...... 1-6
Triggering Switch Logic . . ....... 1-6
7"riggering Modes ....... . ...... 1-6
P-P AUTO ........... . . ...... 1-6
AUTO . . . ............. . . ..... 1-6

THEREMAINING POR770N OF THIS TABLE
OF
NORMaI
. ...............
. . ... 1-6

CONTENTS LIS7 - SERVICING INSTRUCTIONS
.
SINGLE SWeeP .......... . . ... 1-6

7HESE SERVICING lNSl"RUCTIONS ARE FORUSE
Trigger
Coupling
............. ..
1-T

BY QUALIFIED PERSONNEL ONLY .

TO AVOID
AC ... . . .............. . . . . 1-7

ELECTRICALSHOCK, DO NOT PERFORM ANY
AC LF REJ
.............. . .
1-7

SERVICING OTHER THAN '1"HAT CALLED
OUT
IN
AC
HF
REJ
. ............. . .
1-7

THE OPERATING INSTRUCTIONS UNLESS QUALI-
DC ........ ............. . . 1-7

F1ED TO DOSO .
Trigger
Source . .............
. .
1-7
INTernal .... . ............ . . 1-7
LINE ....... . .....,...... . 1-7
EXTernal ... . . .....~~~~~-~
-
1-7

Section 3 1"HEORY OF OPERATION
Trigger Slope ... . ............. 1-8
d'~ARNING
Trigger Level ... . . ............ 1-8

Block Diagram Description ........... 3-1
Horizontal Sweep Rates ........ 1-8

Trigger Generator . ............... 3-1
Time Measurement . . . ......... 1-8

Sweep Generator . ............... 3-1
Sweep Magnification .. ......... 1-8

Pickoff Amplifiers and Delay
Variable Hold Off ..... . ........ 1-8

Gate Generator . . . . . . . ........... 3-1
Delay-Time Operation . . ........ 1-8

Logic ........... . . . . ........... 3-1
TIME Operation .... . ........ i-11

Digital Voltmeter ... . . . . .......... 3-1
TIME Operation in a

Detailed Circuit Description . .......... 3-3
Dual-Beam Oscilloscope

Logic Fundamentals .... . ......... 3-3
Mainframe ......... . . ...... 1-11

Non-Digital Devices .... .......... 3-3
Mainframe
Operating Modes . .... 1-11

Front-Panel Distribution . . ......... 3-6
REV AUG 1981

I

7885 Instruction
Section 3 THEORYOF OPERATION (cont)

Comparator (SN B088750 & Up) . 3-21
Comparator
(SN 8088749 &
Trigger Generator ........ . . ......
3-6

Below)
... . .................. 3-21
External Source ...... . . .......
3-6

Ramp
Control ................ 3-21
Internal and Line Source
........ 3-6

Divide by 4 Counter .......... . . 3-21
Trigger Source Selector
and

Timer .... ............... . . . . 3-21
Amplifier ....... . . . . ..........
3-6

Reference Current Source
Peak-to-Peak Auto ...........
. 3-8

(SN
~088750 & Up) ....... ..... 3-22
Slope Selector
and Trigger

Reference Current Source
Generator
.. .
. . .............
. . 3-8

(SN ~088749 & Below) ... . ..... 3-22
Gate Generator
........... . . . . 3-9

Reference Current Inverter
Logic ..... . ............. ~ ~ ~~~~.
3-10

(SN
~088750 & Up) .... . . ...... 3-22
Sweep Modes
......... . ...... 3-10

Reference Current Inverter
Hold Off
Timing ....... . ....... 3-11

(SN B088749 & Below) ... ...... 3-22
Lockout
Buffer Amplifier ........ 3-11

Reference Current Switch .......
3-22
Hold Off
Generator . . . ......... 3-11

Counter and Encoder
Hold
Off Output Amplifier .......
3-11

(SN B088"750 & Up) . ...........
3-22
Delay
Pickoff Inhibit ........... .
3-12

Counter and Encoder
Delay
Mode Control ........... .
3-12

(SN ~088749 &
Below) ......... 3-22
Auxiliary Y-Axis Generator ... . . .
3-12

Counter Transfer
Control ........ 3-23
Sweep Generator ............ . . . .
3-13

Zero
Count Correction .......... 3-23
Timing Current Source .... . .....
3-13

Time/Division and Readout
Ramp Generator ....... . ......
3-13

Switching ..... ..... ............ 3-23
Output
Preamplifier ... . . .......
3-13

Basic
Readout System ......... 3-23
Sweep Gate Generator
......... 3-16

Time/Division and Readout ..... . 3-23
Pickoff Amplifiers and Delay

Delay Time Readout .......... .
3-23
Gate Generator ..... . ............
3-16

Interface
Connectors and Power
Delay Time Comparison

Supply ............... .... ......
3-24
(SN B088750 & Up) .......... .
. 3-16
Delay 'time Comparison
(SN ~088749 &
Below) ... . ..... 3-16
O 'Time Comparison
(SN ~088750
& Up) .... . . ......
3-16
Time
Comparison

Section
4 MAINTENANCE
(SN ~088749
& Below) .........
3-18
Delay Bias and
Second Delay

Preventive Maintenance ....... . . ....
4-1
Pickoff
Clamp . . ... ........... .
3-18

Cleaning ............... . . . . ....
4-1
Delay
Comparison Voltage

Exterior ............ . ........
4-1
Switch
.... . ...........-. . . . .
3-18

Interior ............. . ........
4-1
Delay Gate
Generator ..... . ....
3-18

Switch Contacts ..... .........
4-1
Symbol
Enable .......... . ...:
3-19

Visual Inspection
. . . . . . . ......... 4-1
Digital
Voltmeter ......... . . ......
3-19

Lubrication ...... . ..............
4-2
Delay
Comparison Voltage
to Ramp

Cam Switch
Lubrication ......... 4-2
Converter (SN ~088750 & Up) ...
3-20

Semiconductor Checks
........... . 4-2
Delay Comparison
Voltage to Ramp

Adjustment
After Repair ......... . . 4-2
Converter (SN ~088749
& Below) 3-21

Troubleshooting
............... . . 4-3
ii

REV AUG 1981
(cont)

REV
AUG 1981
(CONT .)
Page

Page
Section 4 MAINTENANCE (cont)

Section 5 PERFORMANCE CHECK AND
ADJUSTMENT
Troubleshooting Aids ... . . . . ...... 4-3

Preliminary Information .... . . ......
5-1
Diagrams .......... . . . . ...... 4-3

Adjustment Interval .... ........
5-t
Voltages
and
Waveforms
... ..... 4-3

Tektronix Field Service . . . . ...... 5-1
Circuit-Board
Illustrations . . ..... 4-3

Using This Procedure . . .... ....
5-1
Switch Cam Identification . . . ....
4-3

Test Equipment Required .. ........ 5-1
Diode Color Code ........ . . ...
4--3

Special Fixtures ....... . . ...... 5-1
Wiring Color Code ......... . ...
4-3

Test Equipment Alternatives . .... 5-1
Semiconductor Basing ...... . . . .
4-3

Index to Performance Check
Inter-Board Pin Connector

and Adjustment Procedure .... . . . . . 5-4
Identification . . . . . ............ .
4
.,-3

Preliminary Procedure ....... . . . . . 5-4
Multi-Pin Connector Identification .
4-3

A . Triggering System .......... . . . 5-5
Interface Connector Pin
Locations 4-3

B . Horizontal System .......... . . . 5-10
Performance Check and
Adjustment ....... . ........... 4-5
Troubleshooting Equipment ........ 4-5
Troubleshooting Techniques . . . .....
4-6
Troubleshooting Procedure . ..... 4-6

Section 6 INSTRUMENT OPTIONS
Corrective Maintenance ........ . .... 4-10
Obtaining Replacement Parts ... . ... 4-10
Soldering Techniques ........ . . ... 4-10

SeCtiOn 7 REPLACEABLE ELECTRICAL PARTS
Component Removal and
Replacement . . . ............... . . 4-11
Circuit Boards ............ . . . . 4-11

SeCtlOn 8 DIAGRAMS AND CIRCUIT BOARD
Switches ... . .............. . . 4-14

ILLUSTRATIONS
Semiconductors . . ............. 4-14
Interconnecting Pins ........... 4-14
Circuit-Board Pins . ............ 4-15

Section 9 REPLACEABLE MECHANICAL PARTS
Front-Panel Lights . . ........... 4-15
Adjustment
After Repair
...........
4-15
Instrument
Repackaging
..........
4-15

CHANGE INFORMATION
7885 Instruction

7885
Instruction
Fig .
No .

Page

Page
7B85
Delaying ~T'ime
Base ............. .

viii

3-9

Digital Voltmeter detailed block diagram
1-1

Location of release latch
.............. .

1-1

(SN 8088749 & below) . ...............

3-19
1-2

Front-panel controls, connectors,

3-10

Digital Voltmeter timing diagram .........

3-20
and
indicators ... . .................. .

1-2

4-1

Lubrication procedure for a typical cam
1-3

Effects of LEVEL control and SLOPE

switch
.......... . . .................

4-2
switch on crt display ................. .

1-9

4-2

Semiconductor lead
configuration ........

4-4
1-4

Area of graticule used for most accurate

4-3

Inter-boar°d
multi-pin
connector assembly
. .

4-5
time measurements .................. .

1-10

4-4

End-lead multi-pin connector assembly ...

4-5
1-5

Effect of sweep magnifier on crt display . . .

1-10

4-5

Location of
pin
numbers on
Interface
con-
1-6

(A) Delaying-sweep display produced by

necior
............... . .............

4-6
78$5 in the A horizontal compartment . (B)

4-6

7885 troubleshooting chart
............
.

4-8
Delayed-sweep display produced by com-

4-7

Readout board removal procedure .......

4-12
panion time-base unit in the B horizontal

4-8

Coaxial end-lead connector assembly
....

4-13
compartment .... . ............... ... .

1-10

4-9

Cam switch removal procedure .........

4-16
1-7

Typical ,~ (differential) time operation .....

1-12

4-10

Removal procedure for typical push-button
1-8

Measuring time intervals from a triggering

switch .......... . . . . ............... 4-18
event (start of sweep) to any point on a

4-11

Exploded view of circuit-board pin and ferrule 4-19
waveform ..... . .............. . . .....

1-14

4-12

Front-panel light socket assembly ...... .

4-19
1-9

Measuring rise time, fall time, period, fre-
quency, or pulse width in the ;~ (differential)
time mode .... . . ............. . . . . . . .

1-15

The
illustrations in Section 8 are located near
their
1-10

Magnifying a selected segment of the delay-

associated diagrarrr on the foldout
pages .
ing (A) sweep in the delay-time mode with
mainframe alternate or chopped horizontal

8-1

Semiconductor lead configuration .
operation .... . . .............. . ......

1-16

8-2

Location of circuit boards in the 7885 .
1-11

Time-interval measurements in the delay-

8-3

A1--°-Interface circuit board assembly .
time and ,~ (differential) time mode with

8-4

A2-- .-Trigger circuit board assembly .
mainframe alternate or chopped operation
.

1-17

8-5

A3----Readout circuit board assembly .
1-12

Examining an event that occurs
within
a se-

8-6A

A4---(SN B088750 & Up) Digital Voltmeter cir-
lected time interval after a known delay time

cult board assembly .
in the delay-time mode .... . . . . . .......

1-18

8-6B

A4---(SN B088749 & Below) Digital Voltmeter
2-1

7885 dimensional
drawing . . . . . ........

2-4

circuit board assembly .
3-1

Basic block diagram of
the 7885 Delaying

8-7

A1--Interface circuit board assembly .
Time-Base unit ............. . . .......

3-2

8-8

A2---_l"rigger circuit board assembly .
3-2

Detailed block diagram of
Trigger Generator 3-7

8-9A

A4-_-(SN 8088750 & Up) Digital Voltmeter cir-
3-3

Functional diagram of
Trigger Source Selec-

cuit board assembly .
for
...... . ............. . . . . ........

3-8

8-98

A4n-(SN
~088749 & Below) Digital Voltmeter
3-4

Timing diagram
for Gate Generator stage

circuit board assembly .
(092, 096,
098) ......... . . . . ........

3-9

8-10

Readout circuit board assembly .
3-5

Detailed
block diagram of Logic circuit ....

3-10

8-11

Location of Sweep
riming
adjustments .
3-6

Timing diagram for

Delay

Pickoff

Inhibit

8-12

Location of Triggering
adjustments .
stage .... . ............. . . ..........

3-12

8-13A

(SN B088750

&

Up)

Location

of

Digital
3-7

Detailed block diagram of Sweep Generator 3-14

Voltmeter adjustments .
3-8

Detailed block diagram of Pickoff Amplifiers

8-138

(SN 8088749 & Below) Location of Digital
and Delay Gate Generator . ............

3-17

Voltmeter adjustments .
IV

REV AUG 1981

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

7885 Instruction
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 mustbe properly grounded . 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 arepresent in this instrument . The protective instrument covers must not be removed by
operating personnel . Component replacement and infernal adjustments mustbe referred to qualified service personnel
.
Do Not
Service or Adjust Alone
Do
not service or make internal adjustments to This instrument unless another person, capable of giving first aid
and resuscitation, is present .
tMl4RNING
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 .
REV AUG 1981

vii

7885 Instruction
viii
J
J
J
J
J
J
J
TR,c~o
LEVEL
0 ~ ~

MODE

CTS)PtfkG

SCUH('
P-P AUTO

AC

ih ;
AUTO

AC Lf REJ
7885 Delaying Time
Base
AC HE RfJ
SWP
CAL
TEKTRONIX'S
1MS2
1

D
ELAYING
TIME
BASE
7B85
1961-80A
REV AUG 1981

The 7885 Delaying TimeBase 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 .
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 X10 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 .
fi`~~~,~1~ .>~_~`~C ~I
The time-base unit is designed to operate
in
the
horizon-
tal plug-in compartment of the
mainframe .
l~his 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 remove the unit, pull the release latch (see Fig . 1-1)
and pull it out of the plug-in compartment .
RELEASE
LATCH
,Mn
~Bp8~5

DELAYING TIME BASE
_ _ .___ 1___ ._ ._ ___

. __ _ . . .___ .___ _ .
Section 1 ~-71385
-, C 1960-13~
To
install the unit in a plug-in compartment, push it in
until it fits firmly into the compartment . The front panel of

Fig . 1-1 .
Location of release latch .
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

el . Figure 1-2 provides a brief description of all front-panel
is given under Sweep Functions in the Functional Check

controls, connectors, and indicators . More
detailed
informa-
procedure in this section .

lion is given in the General Operating Instructions
.
~UN~T°I®NmAL . ~H~~K
The following procedures are provided for checking
basic
instrument functions . Refer to the description of the con-
C NI~i~~l~~, CONN

1"C)H~, ,GNU

trots, connectors, and indicators while performing this pro-
cedure . If performing the functional check procedure reveals
INUI~A~°~H

a malfunction or possible improper adjustment, first check
the operation of the associated plug-in units, then refer to
All
controls, connectors, and indicators required for the

the instruction manual for maintenance and adjustment
operation of the time-base unit
are located on the front pan-

procedures .
REV
AUG 1981

1-1

Operating Instructions--7885
III
~~J~
I
I
.
~~

~
I

I~
.
, .
v'
;
" 1
~ .`
:
Fig . 1-2 . Front-panel controls, connectors, and indicators .
RI=V AUG 1981

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--Illuminates when sweep circuit is armed (SINGLE SWEEP Model
.
TRIG'D Indicator--Illuminates when the display is triggered .
MODE
Pushbuttons---Selects the operating mode of the triggering circuits .
COUPLING Pushbuttons-Selects the method of coupling the trigger signal to triggering circuit .
~]

SOURCE Pushbuttons-Selects source of the trigger signal .
POSITION
Control-Provides horizontal positioning .
FINE Control-Provides precise horizontal positioning .
TRIGGERING
SWEEP
~()

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 .
~2

TIME/DIV Switch-Selects the sweep rate of the sweep generator .
Operating Instructions-7885
13

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
.
14

SWPCAL Adjustment-Compensates for basic timing changes due to the differences in sensitivity of mainframes in which
the 7885 may be used .
EXTERNAL TRIGGER INPUT
15

EXT TRIG
ATTENUATOR-Selects attenuation factor for external trigger signals .
Js

EXTTRIG 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
18

DELAY TIME Control-Provides variable delay time before the start of the delayed sweep produced by companion time-
base unit .
19

TRACE SEP
Control
and
Switch-Enables ~
TIME functions and provides vertical separation of the delayed sweep
traces (~ TIME operationl .
Z~

~ TIME Control-Provides differential time 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 .
Fig . 1-2 . Front-panel controls, connectors, and indicators (coot .) .
REV
AUG 1981

1- 3
1960-14

Operating Instructions~~-7885
Setup Procedure

6 .
Turn
the
FINE control and note that the display can be
1 . Install the 7B85 in the A horizontal compartment of

precisely positioned horizontally .
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

INl'
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
Delaying and Delayed Sweep .
Perform the following
Normal Sweep .
Perform the following procedure to ob-

procedure to obtaan delaying- and
delayed-sweep displays
tain a normal sweep
and to demonstrate the function of the

and to demonstrate the
function of the related controls . - fo
related controls .

obtain a delayed-sweep display, a
companion time-base unit
must be installed in the
B horizontal compartment of the
mainframe .
1 . Perform
the preceding Setup Procedure .
1 . Obtain a display as described in the preceding Normal
2 .
Connect a 0 .4 V, 1 kHz signal from the mainframe

Sweep procedure .
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 .
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%
(-i--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 (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) .
2 . Press the B S"CARTS AFTER DLY button .
3
.
Set the mainframe horizontal mode for chopped
operation .
4 . Set the companion time-base unit sweep rate
for
5 . Turn the POSITION
control and note that the trace

0 .1 ms/div, and triggering for p-p auto mode, ac
coupling,
moves horizontally .

internal source, and ~- slope .
1- 4

REV AUG 1981

5 . Adjust the mainframe B
sweep
intensity
and check for

1 . Obtain a display as described in the preceding Normal
an intensified zone about 1 division wide on the delaying (A)

Sweep procedure .
sweep display . Also note that the delayed (B) sweep pro-
vides an expanded display of the intensified portion of the
delaying (A) sweep .

2 . Press the AUTO MODE button and turn the LEVEL
control fully counterclockwise to obtain
a
free-running
sweep .
6 . Position the start of the delaying (A) sweep to the left
edge of the graticule .
3 . Slowly turn the HOLD OFF control clockwise and
note that a stable display can be obtained at several posi
7 . Adjust the DELAYTIME control for a crt readout (bot-

tions of the HOLD OFF control . Return the HOLD OFF
con-
tour
division
of crt graticule) of 5 .000 ms . Check that the left

trot to the fully counterclockwise (MIN) position .
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 (B) sweep unit
sweep rate to 20 ~s/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
B 1"RIGGERABL .E
AFTER DLY button and check that the
intensifed zone
moves to the front corner of the next displayed
square
wave .
~ (Differential) 1`IME . Perform the following procedure
to obtain a O (differential) time display and to demonstrate
the function of the related controls .
1 .
Obtain a delaying (A) and delayed (B) sweep display
as described in steps 1 through 4 of the preceding Delaying
and Delayed Sweep procedure .
6 . Press the EXT SOURCE button and set the amplifier
unit deflection factor for a 4-division display .
2 . Turn the l'RACE SEP control counterclockwise
out of
the OFF (detent) position .
7 . Press the AC, AC HF REJ, and DC COUPLING but-
tons for both the
+
and -- positions of the SLOPE switch
3 . Set the DELAYTIME and O 1"IME controls to the fully

and check for a stable display (LEVEL control may be
counterclockwise position .

Check for two delayed (B)

adjusted, if necessary, for a stable display) .
sweeps and note that the crt readout (bottom right of crt) is
0 .000 ms .
8 . Press the AC COUPLING, INl' SOURCE, and NORM
MODE
buttons . Adjust the LEVEL control for a stable
4 . Slowly
turn the ,~ TIME control clockwise and note

display .
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

9 . Press the
AUTO MODE button and adjust the LEVEL
zone and the left
edge of the second intensified zone . Also

control
for
a free-running display .
note that the lower delayed
(B) 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

11 . Adjust the LEVEL control for
a stable display and
controls .

press the SINGLE SWP MODE button .
REV AUG
1981

1-5
Operating Instructions-w-7B85
NOTE"
The
HOLD OFF control varies the sweep holdoff time,
which effectively
changes the repetition rate of the
horizontal sweep signal . However,
its primary function
is to obtain
a stable display of co~r~plex 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 necessary,
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 .
10 . Press the NORMMODE
button and check for no
display .

Operating
Instructions-T~85
12 . Note that
one trace occurs when the RESET MODE

When the trigger
repetition rate is outside the parameter
button is
pressed .

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
13 . Disconnect the mainframe calibrator
signal from the

trace (1'RIG'D light off) . When an adequate trigger signal is
amplifier unit input and press the RESET
MODE button .

again applied, the free-running condition ends and a
trig
Check for no display and note that the READY
indicator is

gered display is presented .
lit .
The P-P AUTO MODE is particularly useful
when observ-
14 . Note that one trace occurs and
that the READY indi-

ing a series of waveforms, since it is not necessary to
reset
cator extinguishes when the mainframe calibrator
signal is

the LEVEL control for each observation . The
P-P AUTO
connected to the amplifier unit input .

MODE is used for most applications because of
the
ease
of
obtaining a triggered display . The AU1 - O,
NORM, and SIN-
GLE SWP MODE settings
may be used for special
applications .
~ NE AIm ~F ~~lTINC
INS°®RIi~ATI~N
AUTO
Triggering
Switch Logic
The AUTO MODE
provides a triggered display with the
The MODE, COUPLING, and SOURCE
push buttons of

correct setting of the LEVEL
control whenever an adequate
the TRIGGERING switches
are arranged in a sequence that

trigger
signal
is
applied (see Trigger Level discussions) . The
places
the most-often used position at the top of each se-

TRIG'D
light indicates when the display is triggered .
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

When the
trigger repetition rate is outside the frequency
applied and the LEVEL control is correctly set, the unit is

range
selected by the COUPLING switch or the trigger
sig-
triggered as indicated by the illuminated TRIG'D light . If the

nal is inadequate, the sweep free runs at the rate
indicated
1'RIG'D light is not on, the LEVEL control is either at a set-

by the TIME/DIV switch (TRIG'D indicator off) . An adequate
ting outside the range of the trigger signal applied to this

trigger signal ends the free-running condition and a triggered
unit from the vertical unit, the trigger signal amplitude is in-

display is presented . The sweep also free runs at the
rate
adequate, or its frequency is below the lower frequency
limit

indicated by the TIME/DIV switch when the
LEVEL control
of the AC COUPLING switch position . If the desired display

is at a setting outside the amplitude
range
of
the trigger
is not obtained with these buttons pushed in, other selec-

signal . This type of free-running display is useful
when it is
tions must be made . Refer to the following discussions or

desired to measure only the peak-to-peak amplitude of a
the instruction manuals for the associated oscilloscope

signal without observing the waveshape (such as
bandwidth
mainframe and vertical units) for more information
.

measurements) .
Triggering Modes

NORMaI
The MODE push-button
switches select the mode in

The NORMMODE provides a
triggered display with the
which the sweep is
triggered .

correct setting of the LEVEL control whenever an adequate
trigger signal is applied . The'TRIG'D light indicates
when the
display is triggered .
P-P AUTO
The P-P AUTO
MODE provides a triggered display at

The normal trigger mode must be
used to produce trig-
any setting of
the LEVEL control whenever an adequate

gered displays with trigger repetition
rates below approxi-
trigger signal is applied . The range of the LEVEL control in

mately 30Hz . When the TRIG'D
light is off, no trace is
the P-P AUTO MODE is between approximately 10% and

displayed .
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

SlNGL~ SWeeP
trigger circuits automatically compensate for a change
in
trigger signal amplitude . Therefore, if the
LEVEL control
is

When the signal to be displayed is not repetitive or varies
set to start the waveform display at a certain percentage

in amplitude,
waveshape, or repetition rate, a conventional
point on the leading edge of a low-amplitude signal, it
trig-

repetitive type
display may produce an unstable presenta-
gers at the same percentage point on the leading edge of a

tion . Under these circumstances, a stable display can often
high-amplitude signal if the LEVEL control is
not changed .

be
obtained by using the single-sweep feature of this unit
.
1- 6

REV AUG 1981

Operating Instructions-~-7E85
The single-sweep mode is also useful
to photograph non-

LF REJ position provides the best
alternate-mode vertical
repetitive or
unstable displays .

displays at fast sweep rates
when comparing two or more
unrelated signals .
To obtaan
a single-sweep display of a repetitive signal,
first obtain the best possible display in the NORM MODE .

AC HF
FtEJ
. AC
HF REJ COUPLING passes all low-fre-
Then, without changing the other TRIGGERING controls,

quency
signals between approximately 30Hz and 50 kl-iz .
press the SINGLE SWP RESET button . A single trace is

Dc is rejected,
and signals outside the above range are at-
presented each time this button is pressed . Further sweeps

tenuated .
When triggering from complex waveforms, this
cannot be presented until the SINGLE SWP RESEI~ button

position is useful to
provide a stable display of the low-
is pressed again . If the displayed signal is a complex

frequency
components .
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

DC . DC COUPLING can be used to provide stable trig-
persistence, allow the display to disappear
before pressing

Bering from low-frequency signals that would be attenuated
the SINGLE SWP RESET button again
.
At fast sweep

in other COUPLING switch positions . DC COUPLING can
rates, it may be difficult to view the single-sweep
display .

be used to trigger the sweep when the trigger signal reaches
The apparent trace
intensity
can be
increased by reducing

a do level set by the L . .EVEL control . When
using internal
the ambient
light level
or by
using a viewing hood as recom-

triggering, the setting of the vertical unit
position control af-
mended
in the mainframe instruction manual .

fects the triggering point .
When using the single-sweep
mode to photograph

Trigger Source
waveforms,
the graticule may have to be photographed sep-
arately,
in
the normal manner,
to prevent over-exposing the

The TRIGGERING SOURCE push buttons select
the
film .
Be
sure the camera system is well protected against

source of the trigger signal connected to the trigger circuits .
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-

INTernal . The INT position connects the
trigger signal
pletely symmetrical . Otherwise, multiple waveforms may

from the vertical plug-in unit .
Further selection of the internal
appear on the film . For random signals, the lens can be left

trigger signal may be provided by
the vertical plug-in unit or
open until the signal triggers the unit . Further information on

bY the
mainframe ; see
the instruction manuals for these in-
photographic techniques is given in the appropriate camera

struments for more information . For most applications, the
instruction manual .

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 EXl~ positions of the
Trigger Coupling

SOURCE
switches must be used .
The TRIGGER COUPLING push buttons select
the meth-
od in which the trigger
signal
is connected to
the trigger

LINE . l"he LINE position connects a sample of the pow-
circuits . Each position permits selection or rejection of some

er-line voltage from the mainframe to the trigger circuit . Line
frequency components of the signal that
triggers
the sweep .

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
AG . AC COUPLING blocks the do component of the
trig-

complex waveform .
ger signal . Signals with low-frequency
components below
approximately 30Hz are attenuated . In general, AC COU
PLING can be used for most applications . However, if the

EXTernal .
The EXT position connects the signal from the
signal contains unwanted frequency components or
if
the

EXT TRIG IN connector to
the trigger circuit . The external
sweep is to be triggered at a low repetition rate or do
level,

signal must be
time-related to the displayed waveform for a
one of the other COUPLING
switch positions will provide a

stable display . An external trigger signal can be used to pro
better display .

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
AC LF REJ . AC
LF REJ COUPLING rejects dc, and at-

useful when signal tracing in amplifiers, phase-shift net-
tenuates
low-frequency trigger signals below approximately

works, wave-shaping circuits, etc . The signal from a
single
30
kHz . Therefore, the sweep is triggered only by the high-

point in the circuit can be connected to the EXT
TRIG IN
er-frequency components of the trigger signal . This position

connector through a probe or cable . The sweep is then trig-
is
particularly useful for providing stable triggering if the trig-

gered by the same signal at all times and allows amplitude,
ger
signal contains line-frequency components . Also, the AC

time relationship, or waveshape changes of
signals
at
var-
REV AUG 1981 1-7

Operating Instructions-7885
ious points in the circuit to be examined without resetting

A calibrated sweep rate can be obtained in any position
the 'TRIGGERING controls .

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
The -: 10 push buttons attenuates the external trigger

to switch between calibrated and uncalibrated displays .
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 .

Time Measurements
When
making
time measurements
from the
graticule,
the
Trigger Slope

area between the second and tenth vertical lines of the
graticule provides the most linear time measurements (see
'The TRIGGERING SLOPE switch (concentric with the

Fig . 1-4) .
Position the start of the
timing
area to
the
second
TRIGGERING LEVEL control)
determines
whether
the
trig-

vertical
ine
and adjust the
TIME/DIV
switch so
the
end of
ger circuit responds on the positive- or negative-going por-

the timing area falls between the second and tenth vertical
tion of the trigger signal . When the SLOPE switch is in the

lines .
( +-)
(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

Sweep Magnification
the SLOPE switch is often unimportant . However, if only a
certain portion of a cycle is to be displayed, correct setting

The sweep magnifier can be used to expand the display
of the SLOPE switch is important to provide a display that

bY a
factor of 10 . The center division of the unmagnified
starts on the desired slope of the input switch .

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
Trigger Level

adjusting the POSITION and FINE POST"fION controls to
bring the desired portion into the viewing area .
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

When the MAG switch is set to X10 (OUT), the equiv-
circuit responds at a more positive point on the trigger sig-

alent magnified sweep rate can be determined by dividing
nal . When the LEVEL control is set in the - region, the

the TIME/DIV setting by 10 ; the equivalent magnified sweep
trigger
circuit responds at a more negative point on the trig-

rate is displayed on
the crt
readout
.
ger signal . Figure 1-3 illustrates this effect with different
settings of the SLOPE switch .
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 I_EVFL 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 .
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 TIMEIDIV control must be in the calibrated position
and the MAG switch set to X1 to obtain the sweep rate

delay-Time Operation
indicated by the TIME/DIV switch . However, the mainframe

A 7B85 installed in the mainframe A horizontal compart
crt readout will display the appropriate sweep rate .

ment can delay a companion time-base unit installed in the
B horizontal compartment . When operating the 7885 in a
The VARIABLE TIME/DIV control includes a two-

delaying mode (B DELAY MODE switch set to B STARTS
position switch to determine if the sweep rate is calibrated,

AFTER DLY or B T'RIGGERABLE AFTER DLY), an intensi-
or uncalibrated . When the VARIABLE control is pressed in,

fled zone is provided on the delaying sweep display during
it is inoperative and the sweep rate is calibrated . When

the time that the companion time-base unit runs (see Fig .
pressed and released outward, the VARIABLE control is ac-

1-6) . A delayed-sweep trace is provided by the companion
tivated for uncalibrated sweep rates, to at least the sweep

time-base unit, corresponding to the intensifed zone on the
rate of the next slower position .

delaying trace, at the sweep rate set by the TIME/DIV
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
1- 8

REV AUG 1981

CRT DISPLAY
OBTAINED WITH
SLOPE SWITCH
SET TO POSITIVE (+)
CRT DISPLAY
OBTAINED WITH
SLOPE SWITCH
SET TO NEGATIVE
(-)
TRIG'D
~dOO p~ al
LEVEL
" _+
TR16'D
3dOOpC~
LEVEL
"
_
TRIG'D
~3dOOpL~
LEVEL
0
(SLOPE)
.. .s
POSITIVE
SLOPEI+) '"
Fig . 1-3 . Effects of LEVEL
control and SLOPE switch on crt display .
Operating Instructions-~-7B85
C1960-30
REV
AUG 1981

1- 9

Operating Instructions---7B85
SECOND-VERTICAL
LINE
1
Fig . 1-4 . Area of graticule used for most accurate time
measurements .
Fig . 1-6 . (A) Delaying-sweep display
producedby 7B85 in the
A horizontal compartment .
(B) Delayed-sweep display pro-
duced by companion
time-base unit in the B horizontal
compartment .
switch of the companion time-base unit (see 1=ig . 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
B .
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-
Fig .
1-5 . Effect of sweep magnifier on crt display .

fied zone on the
delaying-sweep trace and the correspond-
1- 1 0

REV
AUG 1981

OperatingInstructions-7B85
ing delayed-sweep trace is controlled by the triggering

symbol
indicates that the TIME/DIV VARIABLE control is
controls of the companion time-base unit when the 7B85 is

activated or that the B DELAY MODE switch is set to B
in the B TRIGGERABLE AFTER DLY
mode .

TRIGGERABLE AFTER DLY and, therefore, the differential
time is uncalibrated .
Delay-time measurements must be made with the B DE-
LAY MODE switch set to B STARTS AFTER DLY . When

The TRACE SEP control vertically positions the second
the B DELAY MODE switch is set to B 'TRIGGERABLE

delayed-sweep trace with respect to the first delayed-sweep
AFT ER DLY, the delayed sweep starts with the first trigger

trace . Vertical positioning of the delayed-sweep traces with
pulse after the delay time shown on the crt readout . There-

respect to the delaying-sweep trace is provided by the verti
fore, precision time measurements cannot be made in this

cal separation control on the oscilloscope mainframe .
mode because the time delay is only partially dependent on
the DELAY TIME control . The crt readout displays the
greater-than symbol (>) preceding the delay time when op-

0 TIME Operation in a Dual-Beam Oscilloscope
erating in the B TRIGGERABLE AFTER DLY mode to indi-

Mainframe . The 7885 O TIME function is compatible with
Gate that the delay time is uncalibrated . However, the B

7000-series dual-beam mainframes and operation is basical-
TRIGGERABLE AFTER DLY mode is useful for triggering

l
ythe
same as given for ~ 'Time Operation . The 7885 must
on wavefoms
with
excessive fitter
.

be installed in the A horizontal compartment and the com-
panion time-base unit must be installed in the B horizontal
compartment, as with conventional four plug-in compart
`TIME Operation

ment mainframes . Set the horizontal mode switch so that
the 7B85 provides horizontal deflection for one beam and
The ~ TIME delaying
mode provides the best means of

the companion time-base unit provides horizontal deflection
making differential time measurements . The 7B85
can delay

for the other beam . Apply the input signal to the desired
a companion time-base unit at two separate delay times . At

vertical

lu

m unit and select that unit for vertical deflection
the end of the first delay time (determined by the
7885
DE-

p g
.
of both beams .
LAY TIME control and TIME/DIV switch)
an intensifed zone
is provided on the delaying-sweep trace . Further,
a separate
delayed-sweep trace corresponding to the first intensifed

Operation of the ~ TIMEmode in dual-beam mainframes
zone is provided . At the end of the second delay time (deter-

with a dedicated vertical system differs slightly from conven-
mined by the 7B85 TIME/DIV switch, the DELAY TIME, and

tional dual-beam mainframes with vertical-mode switches .
d TIME controls) a second intensifed zone and correspond-

The plug-in unit in the left vertical compartment provides
ing second delayed-sweep trace are displayed (see Fig . 1-7) .

vertical deflection of beam 1, and the plug-in unit in the right
The 7885 must be installed in the A horizontal compart-

vertical compartment provides vertical deflection for beam
ment . The companion time-base unit must be installed in the

p . Therefore, the input signal must be applied to the units in
B
horizontal compartment . The TRACE SEP control must

both the left and right vertical compartments for O TIME
be rotated counterclockwise out of the switch detent posi-

operation .
tion for ~ TIME operation . The sweep rate for the delaying-
sweep trace is determined by the 7B85 TIME/DIV switch,
and the sweep rate of the intensified zones and correspond-

Mainframe Operating Modes
ing
delayed-sweep display is determined by the sweep rate
setting of the companion time-base unit .

The
7885 can also be operated either as an independent
time base in any 'TEKTRONIX
7700-, 7800-, and 7900-Se-
ries
mainframes,
or as a delayed-sweep unit (B DELAY
The differential time between the start
of the
first
intensi-

MODE switch set to INDEPENDENT) in those mainframes
fied zone and the start of the second intensified
zone is

that have two horizontal compartments . A companion
de-
displayed on the crt readout (see Fig . 1-7) . A0
symbol pre-

laying time-base unit (e .g ., another
7885) is required
for
de-
ceding the delay-time readout indicates a differential
mea-

layed-sweep operation . Refer
to
Applications in this
section
surement . The > (greater-than) symbol following
the 0

for additional information .
REVAUG 1981

1- 1 1