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o Service Manual
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o Tektronix
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o 494A& 494AP
o SpectrumAnalyzers
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o Volume 1
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o Warning

o The servicing instructions are for use by qualified
personnelonly. To avoid personal injury, do not

o perform any servicing unlessyou are qualified to
do so. Refer to the Safety Summary prior to

o performing service.

o Pleasecheck for change information at the rear
of this manual.
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o First Edition: January1987

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Copyright @ Tekrronix, Inc. 1987. All rights reserved.
a
Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes
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that in all previously published material. Specifications and price change privileges reserved.

Printed in the U.S.A.
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Tektronix, Inc., P.O.Box 1000, Wilsonville, OR 97070_1000
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TEKTRONIX and TEK are registered trademarks of Tektronix. Inc. o
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o RELEASE COPYRIGHT
OF
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o Tektronix cannotprovidemanuals measurement
for
longereligiblefor longterm support. Tektronix
products that are no
herebygrantspermission
o and licensefor othersto reproduce distribute
and copiesof any Tektronix
o measurement
manuals,
productmanual,
servicemanuals, the like,that (a) havea Tektronix
and
including usermanuals, operato/s
part
o Numberand (b) are for a measurement
supported Tektronix. Tektronix
by A
productthat is no longer

a changes
manualmay be revisedto reflect
madeto the productduringits manufacturing Thus,
life.
o differentversions a manual
of
should takento ensure
be
mayexistfor anygivenproduot.
thatone obtains propermanual
the
Gare
version for
I a specificproductserialnumber. This permission licensedoesnot
and
o applyto any manualor otherpublication is still available
that
Tektronix, to any manualor otherpublication a videoproduction
or for
from

o product a colorprinterproduct.
or Tektronix
accuracy completeness the information,
or of
does not wanantthe
text,graphics, schematics,
O partslists,or othermaterialcontained withinany measurement product
o manualor otherpublication is not suppliedby Tektronix that is
that
produced distributed accordance the permission license
or
or

o set forthabove.
in
TEKTRONIX SHALL
with
NoT BE LIABLE
and
FoR ANY
o DAMAGES WHATSOEVER
CONSEQUENTIAL INCIDENTAL
OR
(|NCLUD|NG, WTTHOUT
DAMAGES,
LtMtTATtON,
FOR
ANy

o LOSS PROFITS,
OF BUSINESS INTERRUPTION. FOR
DAMAGES
OR
o TNFRTNGEMENTTNTELLECTUAL
OF
THEUSEOF ANYMEASUREMENT
pROpERTylAR|S|NG
PRODUCT OR
MANUAL OTHER
OUTOF

o PUBLICATION PRODUCED DISTRIBUTED ACCORDANCE
OR IN
o WITHTHEPERMISSION LICENSE AND SETFORTH ABOVE

o Thomas Lenihan
F. Chieftntellectual
Property
CounselTektronix, (503)627-7266
tnc
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I WARRANTY
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I Tektronix warrants that this product will be free from
o year from the date of shipment. If any such product
defects in materials and workmanship fbr a period of one (l)
proves defective during this warranty feriod, Tektronix, at its
o option, either will repair the defective product without charge for parts
exchange for the defective product.
and labor, or will provide a replacementin

I In order to obtain service under this warranty, Customer must
I of the warranty period and make suitable arrangementsfor
notify Tektronix of the defect before the expiration
the performance of service. Customer shall be
O responsible for packaging and shipping the defective product
to the service center designatedby Tektronix, with
o shipping charges prepaid- Tektronix shall pay for the return of
location within the country in which the Tektronix service
the product to Cusromer if the shipment is to a

I paying all shipping charges,duties, taxes, and any
center is located.customer shall be responsible for
other charges for products returned to any other locations.
t
o This warranty shall not apply to any defect, failure or damage
caused by improper use or improper or inadequate
maintenance and care' Tektronix shall not be obligated to furnish
service under this warranry a) to repair damage
I resulting from attempts by personnel other than Tektroriix
b) to repair damageresulting from improper use or connection
representativesto install, repair or service the product;

I product that has been modified or integrated with other products
to incompatibleequipment;or c) to servicea

o when the effect of such modification or
integration increasesthe time or difficulty of servicing the product.

o TIIIS WARRANTY IS GIVEN BY TEKTRONTX WITH RESPECT
o ANY OTI{ER WARRANTIES, EXPRESSED OR IMPLIED.
TO THIS PRODUCT IN LIEU OF
TEKTRONIX AND ITS VENDORS

o DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY
PARTICULAR PURPOSE. TEKTRONIX'RESPONSIBILITY
OR FITNESS FOR A

o TO REPAIR OR REPLACE DEFECTIVE
PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED
TO THE CUSTOMER FOR
o BREACH OF THIS WARRANTY. TEKTRONIX AND ITS VENDORS
WILL NOT BE LIABLE FOR ANY

o INDIRECT' SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
WHETHER TEKTRONIX OR THE VENDOR HAS ADVANCE
DAMAGES IRRESPECTIVE OF
NOTICE OF TIM POSSIBILITY OF
t SUCH DAMAGES.

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o 494A/494AP
o ServiceVot.1

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o PREFACE
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I This manual contains servic informationfor the . ANSIY1.1- Abbreviations
o TEKTRONfX 494A1494Ap. The information tocatedin
is
two volumes. Volume1 containsthe text and Volume2 . ANSIY32.2- GraphicSymbots
a contains the diagrams and parts lists. The Tabte of
Contents in each volume lists the contents of both
o IEEE91 - Logic Symbots

O volumes.
Change/History Inf ormation
I Manuals
are:
that describeother aspectsof the product
Sometimesinstrumentchanges occur or manual
a . Operator's
Manual
errors are found that make some of the information
the manual inaccurate.When that happens,Manual
in

o . Operator's
Handbook
ChangeInformation noticesare insertedat the rear of
the manual.This helpsensure that the manualcontains
I o Programmer's
Manual the latestand most accurate
the productis sold.
information available
when
I o Programmer's
Reference
Guide
o Who Should Use This Manual?
History information, with the updated data, is
integratedinto the text or diagrams: Whena text page
t This rnanualis intendedfor electronic
in
technicians
with experience servicingdigital,analog,and rf circu-
is updated,the revisedpages are identifiedby a revi-
sion date in the lowerinsidecornerof the page. When
I itw. Circuit analysis is mostly functionil and shoutd
a diagramis updated,the revisiondate is placedat the

o help isolate most malfunctione a board or block of
to
lower center of the diagram. History informationis
shown with a gray tint. When a componentvalue is
a circuitry.The technicianshould then be abte, with the
aid of test equipment,to isolate the malfunction a to
changed,the designator the drawingis boxedwith a
on
grey outline. Whena circuit is deletedor changed,
o specificcomponent components.
or
This instrumentcontains firmwarethat provides a
originalconfiguration shown in grey, drawn eitherat
its originallocation to the side of the drawing.
or
is
the

O thoroughinstrument check during power up and during lf you havea manualother than the one that came
o operation,
abbreviated
and if needed,guidesthe usei throughai
front-panelcalibrationprocedure. lf cali_
with your instrument may containrevisions
it
applyto your instrument;
that do not
however all historyinforma-
I brationcannotbe achieved, diagnostic
a test detects tion that pertains the earlierinstruments retained.
to is
o and isolates most problems the system,
LO. The technician
to suchas 1st
can then run troubleshootingdiag-
When a major modification has been made to an
assemblyor circuit board, the data for the replaced
o nostics to further isolate the problemto the board or
blockof components. Referto the Maintenance
assernbly will follow the new information and will be
o for diagnostics information.
section identified
instrurnent
with appropriate titles or headingssuch as
serial number range or the assemblyor
I DocumentationStandards
boardpart numbers.

o Most terminology and graphicsfollow ANSI stan_
Also, if your instrument
has an assemblyreplaced
with a newer version,documentation the newer
for
o qalds. A glossaryof terms is providedas an appendix.
Referto the followingstandards:
assemblymay be supplied. Contactany TektronixSer-
viceCenterfor information.
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o 494A/494AP
o ServiceVot. 1

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o TABLEOF CONTENTS
o
o The 494A/494AP
service Manuatis divided into two volumes.

o VOLUME1
o Page
o PREFACE ........................
i Section4 PERFORMANCE CHECK
Page

o TABLE CONTENTS
OF ..............
LISTOF ILLUSTRATTONS...........
..........
iii
Introduction ..,.4-1
a LISTOF TABLES
SERVICING SAFETY
SUMMARY
........
x
.............
xiii
.........
xv
Incoming Inspection
OptionInstrument
Test ......................
Checks..............,......
4_1
4_1
I Verification Tolerance
of Values ............4_1
o Section1 GENERAL INFoRMATION
History Information
Equipment Required
............
..........
4-1
4-1
I productDescription
...........
1_1
PRELIMINARY PREPARATTON .............4-4

a Conformance
Industry
to
Standards
InitialPower-Up
Calibrate
............
Position,
.....44

a Product Service
............
1_1
.................
1_1
CenterFrequency,
Reference Level,
o Instrumnt
Installation
Construction
and
Preparation Use
.... 1-z
,l_2
and Dynamic
PERFORMANCE
Range
CHECK
..........4-s

I Changing
for
powerInputRange
........... pRocEDURE ................ .....4_6
o Replacing Fuses.........
....,.....,.....
1_2 1. Check't0MHz Reference
Oscillator Accuracy ...........4_6
o Selected
Assembly
Components
and
.......1-2 2. CheckCounter Accuracy
3. CheckCounterSensitivity
..................
................
4-6

o CircuitNumbering
Firmware Versionand
..............
1_2 4. CheckCentErFrequency
4-6

o Error MessageReadout .... 1-g
Accuracy
5. CheckCenterFrequency
.,......4-T

o Options
Accessories
..........
1-g
..,....................
1-3
Stability ...........
6. CheckResidual ..........................
FM
4-9
4-9
o 7. CheckFrequency

o Section2 SPEC|F|CAT|ON
Span/Div Accuracy
8. CheckMarkerAccuracy
............
...................
4-10
4-12
o ELECTRICAL ................
Verification Tolerance
.....2-1 9. CheckSweepTime
Accuracy ........4-19
o Frequency
Amplitude
of
Related
Related
Values .....,. Z-1
Characteristics 2-1
Characteristics 2_6
... 10. CheckPulseStretcher
11.CheckResolution
....................
Bandwidth
4-19

t InputSignat Characteristics
....
.............. 1
2-1 and Shape Factor ..........-...4-14
o OutputSignal
General
Characteristics
Characteristics
...........2-1g 12.Check
13.Check
Calibrator Output
NoiseSidebands
..................
..................
4-15
4-15
a ' PowerRequirements
.................... s
2-1
........,.........,.....
2-15 14.CheckFrequency Response ............4-16

o ENV|RONMENTAL..........
PHYSTCAL
... 2_16
.....2-.t7
15.CheckDisptay
Range andAccuracy
16. CheckPreselector
Dynamic
.............................
4-1g

I Ultimate Rejection .........-...4-20
o Section3 INSTALLATION 17. CheckRF Attenuator Accuracy .......4-20

o UNPACKING AND
tNtilAL TNSPECTTON .......,3-1
18. ChecklF GainAccuracy
'l 9. Gheck
GainVariation
..................
Between
4-25

t coNNECTtNG POWER .....3_2
Resolution Bandwidths
20. CheckSensitivity
......4-26
.........4-26
o PowerSourceand
PowerRequirements g_2
........................
21. CheckResidual
Spurious Response ...........4-27
I STORAGE ANDREPACKAGING ......,....
3.2 22. Cheeklntermodulation

a Storage
Repackaging Shipment
for
.....g_2
g-3
................
Distortion
23. CheckHarmonic Distortion
........4-2A
........,..... 4-29
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49441494AP
ServtceVot. i o
o
I
TABLEOF CONTENTS
(Gonr.) .|

r
Section 4 PERFORMANCE
CHECK(Conr.)
page Page
o
24.CheckLO Emission .....4-29
15. AdjustBandLeveling
Waveguide Bands
for
..............
5-25 o
25.Check1 dB Compression point.......4-29 16. PhasE
OPTION
LockCalibration
INSTRUMENTS
....................
ONLY.............
5-2S a
26. CheckExternalReference
InputPower .... 4-31 17. AdjustOption07 VR Band Leveling 5-29
5-29
a
27. CheckTriggeringOperation
and Sensitivity
.............. .....4-31
18. AdjustOption Module.................
42 5-29
o
28. CheckExternal
Section 6 MAINTENANCE I
SweepOperation
29.CheckVERTOUTPUT
...............
Signat..........
4-92
4-34 TNTRODUCTTON ...............................
6-1 o
30. CheckHORTZ
SignafLevel
OUTPUT
....4-94
Removing
lnstrument
the
from its Cabinet .......... 6-1
o
oPTloN TNSTRUMENTS .......................
4_34 static-sensitive components .......6-1 t
31. CheckOption07
Calibrator
Output ...............4-94
PREVENTIVE
Elapsed
MAINTENANCE ...............
TimeMeter .....................
6.2
6-2 a
32. CheckOption07
FrequencyResponse .........4-95
Cleaning
Lubrication
......-............
...............
6-2
6-2
o
33. CheckOption4i Frequency
Span/DivAccuracy
Fixturesand Tools O
34. CheckOption42
............4-gz for Maintenance
Visual lnspection
.................,.........
6-2
..........................
6-2 o
110MHz OUTLevel
35. GheckOptiopn42110MHz tF
..........4-gB Transistor and Integrated
o
OutputBandwidth,CenterFrequency,
Bandpass Ripple,and Symmetry
Circuit Checks
Performance Checks
and Recalibration
..........6-2

.........................
6-3
o
About110MHz ..................4-gg I
GPIBVERIFICATTON PROGRAM .......... 4-39
SavingStoredDatain
Battery-Backup
TROUBLESHOONNG
Memory ...............6-3
........6.3 a
Section 5 ADJUSTMENT
Troubleshooting ...................
Aids 6-9 o
Introduction .... 5-1
Diagrams
CircuitBoard
.............6-3
o
Equipment
ADJUSTMENT
Required
PROCEDURE
..........5-1
................
5-2 LocatorCharts
and
lllustrations Component
..... 6-4 o
PREPARAT|ON ............. .....5-2 Diagnostics .......... 6-4 t
1. AdjustLow Voltagepower Suppty ... 5-3
2. AdjustZ-Axis and
General Troubleshooting
Techniques ...............6-4 o
HighVoltageCircuits .........5-5 Semiconductor
Diode
Checks............
Checks..........................
6-4
6-4 a
3. Adjust Deflection
Gainand Frequency
Amptifier
Response .............
4. Adjust DigitalStorageCalibration.... 5-g
5-6 Diagnostic Firmware
Troubleshooting
................,...
Steps .................
6-5
6-5
a
5. AdjustSweepTiming .... 5-g DTAGNOSTTCS ......................................
6-5 I
TROUBLESHOOTING USING
6. AdjustFrequency GontrolSystem
and Dot Marker Position .... S-g THEERROR MESSAGE DISPLAY 6.5 .... I
7. AdjustLog Amplifier .........................
5-11
Introduction ..............6-5 I
8. Adjust Resolution
andShape Factor
Bandwidth
..............5-14
Combination Error Messages... 6-6
Procedure
of
Format .... 6-6 o
9. Presetthe VariableResolution TRACE MODES
Alternate Frequency
............
Display........
6-14
6-14 o
Gainand BandLeveling
10.AdjustCalibrator
.....,..................
OutputLevet ........
5-19
5-20 Auxiliary Synthesizer Control.......6-14 o
11.AdjustlF Gain
12.Adjust B-SAVEA
..............
S-20 Correction
coRRECTtVE
Disable/Enable
MATNTENANCE
........-...
..............
6-14
6-15 o
Refergnce Level .........
13.AdjustPreselector
.......5-21
Driver................ S-21
Handling
Components
StaticSensitive
.............6-15 o
14.AdjustBandLeveling for Obtaining Replacement
PartsRepairand Return
Parts....... 5 6-1 I
CoaxialBands ...................
5-24
Program ...................
6-15 o
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o 494A/494APService Vot. 1
o
I
O TABLEOF CONTENTS
(Conr.)
I page
I Page

o Section6 MAINTENANCE
(Conr) Preparing 2nd LO
the
o Firmware Versionand
Enor Message Readout............... 5 6-1
Assembly Adjustment
for
Reassembling the
.............
6-35

O SelectedComponents
Replacing EPROM
.................. 5
6-1 2nd LO Assembty
Troubleshooting and Calibrating
.....6-9g

I or ROMDevices ........ 6-15 the 16-20 MHz PhaseLock
a Surface-Mounted
Replacing
Components 6_1
Surface-Mountd
..... 6 Section
Troubleshooting
.....................
Aids for the
6-40

o Components ..............6_17 2182MHzPhaseLocked
2nd LO Assembty
o Transistor
Circuit
and Integrated
Configurations ................,.. 7
6_1 100MHz Osciltator the in
.....6-42

a Diode Cotor
MultipleTerminal
(Harmonica)
Code.........................6_1g 3rd Converter
l st Converter
...............................
649
Bias .....................,.
6-44
I Resistor
Connectors
Values
............... g
6_1 AuxiliarySynthesizer
VCOAdjustment ...........................
6-44
o Capacitor
Soldering
Marking
Techniques
......... 6-1g
.....6_1g
................... g
Baseline Leveling
(VideoProcessor) ..... 6-46
I Replacing Squarepin for
the
6-1
10 MHz Reference
o the Multi-pin Connectors ..............
Servicing VR Module..............
6_1g Oscillator
MICROCOMPUTER
Accuracy
SYSTEM
.. 6-49

o REPLACING
the
ASSEMELIES
ANDSUBASSEMBLTES
6-1g
MATNTENANCE .............
OptionSwitches
.... 6-50
t Removing
....................
and Installing
6_19
Power-up Self Test
.......6-50
... 6-50
o the GPIBBoard
Removing Replacing
.........6-22 Microcomputer
Address Bus Test
SystemTest ........6-51
.....6-52
o Semi-rigid
or
Coaxial Cables............ 6_22 Microcomputer .................
Bus 6-52

o Replacing DualDiode
the
Assembty the 1st Mixer ............
in 6_22
Mernory
Processor
AddressDecoders..... 6-52
Address Decoder 6-59....
a Replaeing Crt
the
Repairing Crt
the
......6_23 GPIBBoard
AddressDecoders 6-s3
o Trace RotationCoil ... 6-29 Clocksahd Control Lines......... 6-54

o