Keithley 3940 User manual

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ontains Servicing Information
Publication Date: August 1991
Document Number: 3940-902-01 Rev. A

WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a
period of 1year from date of shipment.
Keithley Instruments, Inc. warrants the following items for 90days from the date of shipment: probes, cables,
rechargeable batteries, diskettes, and documentation.
During the warranty period, we will, at our option, either repair or replace any product that proves to be de-
fective.
To exercisethis warranty, write or call your local Keithley representative, or contact Keithley headquarters in
Cleveland, Ohio. You will begiven prompt assistanceand return instructions. Sendthe product, transporta-
tion prepaid, to the indicated service facility. Repairs will bemade and the product returned, transportation
prepaid. Repaired or replaced products are warranted for the balance of the original warranty period, or at
least 90 days.
LIMITATION OF WARRANTY
This warranty doesnot apply to defectsresulting from product modification without Keithley’s expresswrit-
ten consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-re-
chargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow
instructions.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANT IES,EXPRESSEDOR IMPLIED, INCLUDING
ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE
REMEDIES PROVIDED HEREIN ARE BUYERS SOLEAND EXCLUSIVE REMEDIES.
NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR
ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USEOF ITS INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS
BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAM-
AGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTSOF REMOVAL AND INSTALLATION,
LOSSESSUSTAINED AS THE RESULT OF INJURY TO ANY PERSON,OR DAMAGE TO PROPERTY.
INSTRUMENT-S
Instruments Division, Keithley Instruments, Inc. l 28775Aurora Road l Cleveland, Ohio 44139 l [phone]* Fax: [phone]
WF.ST GERMANY:
GREAT BRITAIN: Keitbley Instruments GmbH
l Heiglhofstr. 5 l Munchen 70 l 089-71002-O l Telex: 52-12160 l Fax: [phone]
Keitbky
FRANCE:
NETHERLANDS:
SWITZERLAND:
AUSTRIA:
ITALY:
Keithky Instruments, Ltd.
l The Minster l 58, P&man Road l Reading, Berkshire RG 3 X4 l 01144 734 575 666 l Fax: [phone]
Instruments SARL l 3 Allee des Garays l B.P. . l
60.91124 PaIatseau/Z.I. l-6-0115 155. Telex MI0 933 Fax: [phone]
Keithley Instruments BV
l Avelingen West 49 l 4202 MS Gorinchem l l l l l
P.O. Box 559 4200 AN Gorinchem 01830-35333 Telex: 24 684 Fax: [phone]
Keitbley Instruments SA
l Kriesbacbstr. 4 l 8600 Dubendorf l l e
0X321-9444 Telex 828 472 Fax: [phone]
Keitbley Instruments GesmbH
l Rosenhugektrasse 12 l (0222) l
A-1120 Vienna. 84 65 48. T&x: 131677 Fax: [phone]
Keitbley Instruments SRL l Vi& S. Giiano 4/A l 20146 MiIano l 02-4120360 or 02-4156540 l Fax [phone]

Service Manual
Model 3940
Multifunction Synthesizer
01991, Keithley Instruments, Inc.
All Rights Reserved
Instruments Division
Cleveland, Ohio, U. S.A.
Document Number: 3940-902-01

Safety Precautions
The following safety precautions should be observed before using the Model 3940Multifunction Synthesizer and any
associated instruments.
This instrument is intended for useby qualified personnel who recognize shock hazards and arefamiliar with the safety
precautions required to avoid possible injury. Read over this manual carefully before using the instrument.
Exercise extreme caution when ashock hazard is present at the test circuit. The American National Standards Institute
(ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. A good
safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring.
Inspect the connecting cablesand test leads for possible wear, cracks, or breaks before each use.
For maximum safety, do not touch the test cables or any instruments while power is applied to the circuit under test.
Turn off the power and discharge any capacitors before connecting or disconnecting cables from the instrument.
Do not touch any object which could provide a current path to the common side of the circuit under test or power line
(earth) ground. Always make measurements with dry hands while standing on adry, insulated surface capable of with-
standing the voltage being measured.
Instrumentation and accessoriesshould not be connected to humans.

HOW TO USE THIS MANUAL
Details procedures to verify that the instrument meets
stated specifications.
SECTION 1
Performance Verification
Describes basic operating principles for the various circuits in
SECTION 2
the Model 3940.
Principles of Operation
Covers fuse replacement, calibration and repair of the instru-
SECTION 3
ment, and lists replacement parts.
Service Information
WARNING
The information in this manual is intended for qualified serv-
ice personnel who can recognize possible shock hazards. Do
not attempt these procedures unless you arequalified to do so.

Table of Contents
SECTION 1 - Performance Verification
1.1 INTRODUCTION. ............................................................. l-l
1.2 ENVIRONMENTAL CONDITIONS ................................................ l-l
1.3 INITIALCONDTMONS ......................................................... l-l
1.4 LINEPOWERVOLTAGE.. ...................................................... l-1
1.5 RECOMMENDED TESTEQTJIPMENT .............................................. l-l
1.6 VERIEXATION PROCEDURES ................................................... l-2
1.6.1 Frequency and Duty Cycle Accuracy .............................................. l-2
1.6.2 AmplitudeAccuracy .......................................................... l-4
1.6.3 Frequency Response (Sine) ..................................................... 1-6
1.6.4 Frequency Response (Triangle, Sawtooth, Square) .................................... l-7
1.6.5 Frequency Response (Sub Sine) ............................ :. .................... l-8
1.6.6 Total Harmonic Distortion ..................................................... 1-8
1.6.7 DCVoltageAccuracy ......................................................... l-10
1.6.8 DCLevel(Square)andDCOffsetError(Sine) ....................................... l-11
SECTION 2 - Principles of Operation
2.1 INTRODUCTION .............................................................. 2-l
2.2 BLOCKDIAGRAM ............................................................ 2-1
22.1 ControlSection .............................................................. 2-1
2.2.2 Display and Keyboard Section ................................................... 2-1
2.2.3 Trigger Section .............................................................. 2-1
2.2.4 SweepSection ............................................................... 2-1
2.2.5 GMBInterface ............................................................... 2-l
2.2.6 SubSynthesizer ............................................................. 2-3
2.2.7 MainSynthesizer ............................................................ 2-3
2.2.8 PowerSupply ............................................................... 2-3
2.3 MAINSYNTHESIZERDESCRIl?TION .............................................. 2-3
2.3.1 Main Synthesizer Block Diagram ................................................. 2-3
2.3.2 D/AConverter .............................................................. 2-3
2.3.3 SquareWaveGenerator ....................................................... 2-3
2.3.4 Amplitude Control ........................................................... 2-3
2.3.5 OutputAmplifier ............................................................ 2-3
2.3.6 Calibration ................................................................. 23
2.4 SYNTHESIZER OPERATING PRINCIPLES .......................................... 2-5
SECTION 3 - Service Information
3.1 INTRODUCTION .............................................................. 3-1
3.2 LINEFUSEREPLACEMENT ..................................................... 3-1
3.3 CALIBRATION ............................................................... 3-1
3.3.1 EnvironmentalConditions ..................................................... 3-2

3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.3.8
3.4
3.5
3.6
3.6.1
3.6.2
3.6.3
3.7
3.7.1
3.7.2
InitialConditions ............................................................
LinePower............., ...................................................
Recommended Calibration Equipment ............... ; .............................
Cover Removal ..............................................................
CalibrationAdjustments.. .....................................................
CalibrationProcedures ........................................................
CoverReplacement ...........................................................
FANFILTERCLEANING ........................................................
RECHARGEABLE BATTERY REPLACEMENT ........................................
REPAIR .... .................................................................
Factory Service ..............................................................
PowerSupplyTestPoints ......................................................
Board-LevelRepair ...........................................................
REPLACEABLEPARTS .........................................................
PartsList ..................................................................
OrderingParts ..............................................................
APPENDICES
A Typical Data
B Model 3940Specifications
3-2
3-2
3-2
3-2
3-3
3-6
3-8
3-9
3-9
3-9
3-9
3-9
3-11
3-11
3-11
3-11

List of Illustrations
SECTION 1 - Performance Verification
Figure l-l
Figure l-2
Figure l-3
Figure l-4
Connections to Timer/Counter ............................................... l-3
ConnectionstoModel197ADMM ............................................ l-4
Connections to Wideband AC DVM ........................................... l-6
Connections to Audio Analyzer .............................................. l-9
SECTION 2 - Principles of Operation
Figure 2-l
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Overall Block Diagram ..................................................... 2-2
Main Synthesizer Block Diagram .............................................. 2-4
Frequency Synthesizer Address Generator Diagram .... ........................... 2-5
Address Generator Waveform ...... ......................................... 2-6
Waveform Memory and D/A Converter ........................................ 2-6
SECTION 3 - Service Information
Figure 3-1
Figure 3-2
Figure 3-3
Figure 3-4
Figure 3-5
Figure 3-6
Figure 3-7
Figure 3-8
Figure 3-9
CoverRemoval ........................................................... 3-3
Analog Board (NP-10375) Calibration Adjustments ................................ 3-4
Control Board (NP-21007) Calibration Adjustments ................................ 3-5
Sub Synthesizer Output Connections to Model 197A DMM .......................... 3-6
Main Synthesizer Output Connections to Timer/Counter ........................... 3-7
Main Synthesizer Output Connections to DMM .................................. 3-7
DMM Connections to DC OFSand GND Test Points ............................... 3-8
Power Supply Test Points ................................................... 3-10
Model 3940Exploded View .................................................. 3-12

List of Tables
SECTION 1 - Performance Verification
Table l-1 Verification Equipment ..................................................... 1-2
Table l-2 Limits for Frequency and Duty Cycle Accuracy ................................... l-3
Table 1-3 Limits for Amplitude Accuracy ............................................... 1-5
Table 1-4 Limits for Frequency Response (Sine) .......................................... 1-7
Table 1-5 Limits for Frequency Response (Triangle, Sawtooth, Square) .......................... 1-7
Table l-6 Limits for Frequency Response (Sub Sine) ....................................... 1-8
Table 1-7 Limits for Total Harmonic Distortion .......................................... l-10
Table l-8 Limits for DC Voltage Accuracy .............................................. l-10
Table l-9 LimitsforDCLevel(Square)andDCOffsetError(Sine) ............................ l-11
SECTION 3 - Service Information
Table 3-l Recommended Line Fuses ................................................... 3-1
Table 3-2 Recommended Test Equipment for Calibration ................................... 3-2
Table 3-3 Board Level Repair Summary ................................................ 3-11
Table 3-4 Replaceable Parts ......................................................... 3-l 1

SECTION1
Performance Verification
1.I INTRODUCTION
The procedures outlined in this section may be used to
verify that the instrument is operating within the limits
stated in the specifications. Performance verification may
be done when the instrument is first received to ensure
that no damage or misadjustment has occurred during
shipment. Verification may also beperformed whenever
there is a question of instrument accuracy, or following
calibration, if desired.
procedures. If the instrument has been subjected to ex-
tremes of temperature (outside the range specified in the
previous paragraph), additional time should be allowed
for internal temperatures to reach normal operating tem-
perature. Typically, it takes one additional hour to stabi-
lize a unit that is 10°C (18“F) outside the specified tem-
perature range.
1.4 LINE POWER VOLTAGE
NOTE
If the instrument is still under warranty (less
than one year from the date of shipment), and
its performance falls outside the specified
Before performance verification, be sure the line voltage
selector switch setting is setto the correct position. Tests
should be performed with the instrument operating on a
line voltage within 10%of the setvoltage and ataline fre-
quency from 48 to 62Hz.
. A
range, contact your Keithley representative or
the factory to determine the correct course of
1.5 RECOMMENDED TEST EQUIPMENT
action.
1.2 ENVIRONMENTAL CONDITIONS
Table l-1 lists all the test equipment needed for verifica-
tion. The procedure for performance verification isbased
on using this exact equipment.
All measurements should be made at 18-28°C (65-82’F)
and at lessthan 70%relative humidity.
1.3 INITIAL CONDITIONS
NOTE
The verification limits reflect only the accu-
racy specifications of the Model 3940.They do
not include test equipment tolerance.
The Model 3940must beturned on and allowed to warm
up for at least one hour before beginning the verification
Alternate equipment may be used aslong asthe substi-
tute equipment has specifications at least as good as
those listed in Table l-l.
l-l