Fluke Series II User manual

For the benefit and convenience of its customers, Fluke
Corporation (Fluke) has reproduced this copy of amanual
which is no longer in production. This manual has not been
edited or updated since the revision date shown on the lower
left hand corner of the first page. Fluke will not be liable for
any claims, losses or damages of any kind incurred by any
user arising from use of this manual.
FLUKE
77/75/73/70/23/2
1
Series II Multimeter
Service Manual
PN 896204
July 1991 Rev. 1, 9/92
©1992 John Fluke Mfg., Inc. All rights reserved. Lltho in U.S.A. ®

OPERATOR SAFETY INFORMATION
This meter has been designed and tested according to IEC Publication 348. Follow all safety
and operating instructions to ensure that the meter is used safely and is kept in good
operating condition.
•Never use the meter if the meter or test leads look damaged.
•Always turn off power to the circuit before cutting, unsoldering, or breaking the circuit. Small
amounts of current can be dangerous.
•Never measure resistance in acircuit when power is applied to the circuit.
•Never touch the probes to avoltage source when the test leads are plugged into the 10A or
300 mA input jack.
•To avoid damage or injury, never use the meter on unprotected circuits that exceed 4800
volt-amps.
•Never apply more than 1000V dc or 750V ac rms (sine) between any input jack and earth
ground.
•Always be careful when working with voltages above 60V dc or 30V ac rms. Such voltages
pose a shock hazard.
•Always keep your fingers behind the finger guards on the probe when making
measurements.
•Always use a high voltage probe to measure voltage if the peak voltage might exceed
1000V.
SYMBOLS MARKED ON EQUIPMENT
DANGER -High voltage.
Attention -refer to the manual. This symbol indicates that information about
usage of afeature is contained in the manual.
Fuse information.
USE THE PROPER FUSE
To avoid fire hazard, use only afuse identical in type, voltage rating, and current rating as
specified on the case bottom fuse rating label.
DO NOT OPERATE DISASSEMBLED METER
Always operate the meter with case top and bottom properly assembled.
Access procedures and the warnings for such procedures are contained in this Service
Manual. Service procedures are for qualified service personnel only.
DO NOT ATTEMPT TO OPERATE IF PROTECTION MAY BE IMPAIRED
If the meter appears damaged or operates abnormally, protection may be impaired.
Do not attempt to operate it. When in doubt, have the meter serviced.

Table of Contents
SECTION TITLE PAGE
1Introduction and Specifications 1-1
1-1. INTRODUCTION 1-3
1-2. ORGANIZATION OF THE SERVICE MANUAL 1-3
1-3. CONVENTIONS 1-4
1-
4. SPECIFICATIONS 1-4
2Theory of Operation 2-1
2-
1. INTRODUCTION 2-3
2-2. FUNCTIONAL BLOCK DESCRIPTION 2-3
2-3. DETAILED DESCRIPTION 2-3
2-4. Voltage Signal Conditioning 2-3
2-5. Cunrent Conditioning 2-4
2-6. Ohms 2-4
2-7. Additional Circuitry 2-4
2-8. AC CONVERTER 2-4
2-9. ACTIVE FILTER 2-4
2-10. ROTARY SWITCH 2-5
2-
11. A/D CONVERSION 2-5
3Maintenance 3-1
3-
1. INTRODUCTION 3-3
3-2. PCAACCESS AND GENERAL MAINTENANCE 3-3
3-3. DISPLAY ACCESS 3-4
3-4. CLEANING 3-4
3-5. PERFORMANCE TESTS 3-6
3-6. Initial Procedure 3-6
3-7. Display Test 3-6
3-8. DC Voltage Test 3-6
3-9. AC Voltage Test 3-7
3-10. Resistance Test 3-8
3-11. Diode Test 3-8
3-12. DC mA Test (75/21 &77/23 Only) 3-9
3-13. DC Amps Test (73, 75/21, and 77/23 Only) 3-9
3-14. CALIBRATION 3-9
3-15. TROUBLESHOOTING 3-9
3-16. Supplemental Troubleshooting Procedures 3-11

Table of Contents
SECTION TITLE PAGE
3-17. CHECKING THE CRYSTAL OSCILLATOR 3-11
3-18. CHECKING THE REFERENCE VOLTAGE 3-11
3-19. CHECKING DISPLAY DRIVE VOLTAGE 3-11
3-20. CHECKING BEEPER DRIVE SIGNAL 3-11
3-
21. TRACING THE VDC SIGNAL PATH 3-11
4List of Replaceable Parts 4-1
4-
1. INTRODUCTION 4-3
4-2. HOW TO OBTAIN PARTS 4-3
4-3. TECHNICAL SERVICE CENTERS 4-3
5Schematic Diagrams 5-1
ii

List of Tables
TABLE TITLE PAGE
1-
1. Specifications 1-5
2-
1. SI Function Codes 2-6
3-
1. Recommended Test Equipment 3-4
3-2. DC Voltage Test 3-7
3-3. AC Voltage Test 3-7
3-4. Resistance Test 3-8
3-5. DC mA Test 3-9
3-6. DC Amps Test 3-9
5-1. Abbreviations 5-2
Hi

List of Tables
IV

List of Illustrations
FIGURE TITLE PAGE
2-1. Overview 2-3
2-2. Ohms Function 2-5
2-
3. AC and A/D Converter 2-7
3-
1. Assembly Details 3-5
3-2. Display 3-6
3-3. Troubleshooting Tree 3-10
5-1. A1 Main PCA 5-3
5-2. Signal Flow Diagram 5-5
v

List of illustrations

Section 1
Introduction and Specifications
CONTENTS PAGE
1-1. INTRODUCTION 1-3
1-2. ORGANIZATION OF THE SERVICE MANUAL 1-3
1-3. CONVENTIONS 14
14. SPECIFICATIONS 14
1-1

Introduction and Specifications

Introduction and Specifications
INTRODUCTION
INTRODUCTION 1-1.
This manual presents service information for the Fluke 70, 73, 75, 77, 21, and 23 Series
II Multimeters. The manual includes atheory of operation, general maintenance
procedures, performance tests, calibration procedures, troubleshooting information, alist
of replaceable parts, and schematic diagrams.
Ameter under warranty will be promptly repaired or replaced (at Fluke’s option) and
returned at no charge. See the registration card for warranty terms. If the warranty has
lapsed, the meter will be repaired and returned for afixed fee. Contact the nearest
Service Center for information and prices. Alist of U.S. and International Service
Centers is included at the end of Section 4of this manual.
ORGANIZATION OF THE SERVICE MANUAL 1-2.
The following descriptions briefly describe each section in the manual.
SECTION 1. INTRODUCTION AND SPECIFICATIONS
This section describes use of the Service Manual and application of special terminology
(conventions) to describe the meter’s circuitry. Acomplete set of specifications appears
at the end of this section.
SECTION 2. THEORY OF OPERATION
This section first categorizes instrument circuitry into functional blocks, with adescrip-
tion of each block’s role in overall operation. Adetailed circuit description is then given
for each block. These descriptions explore operation to the component level and fully
support troubleshooting and repair procedures defined in Section 3.
SECTION 3. MAINTENANCE
Provides complete maintenance information, from general maintenance and cleaning
instructions to detailed troubleshooting and repair procedures to the component level.
Troubleshooting and repair procedures rely heavily on both the Theory of Operation
presented in Section 2 and the Schematic Diagrams shown in Section 5.
SECTION 4. LIST OF REPLACEABLE PARTS
Includes parts lists for all standard assemblies. Information on how and where to order
parts is also provided.
SECTION 5. SCHEMATIC DIAGRAMS
Includes schematic diagrams for all assemblies.
1-3

Introduction and Specifications
CONVENTIONS
CONVENTIONS 1-3.
Throughout the manual, certain notational conventions are used. Asummary of these
conventions follows:
•Instrument Reference
When the discussion involves common features of the Fluke model 70, 73, 75, 77,
21, and 23 multimeters, the term “meter” is used. Where features differ among
models, further identification is made by model number.
•Printed Circuit Assembly
The term “pea” is used to represent aprinted wiring board and its attached parts.
•Circuit Nodes
Individual pins or connections on acomponent are specified by adash (-) following
the component reference designator. For example, pin 19 of U30 would be U30-19.
•User Notation
Generally, push buttons, function positions, input terminals, and display notation are
presented in this manual as they are seen on the meter.
Special terms (mnemonics) used in text descriptions of meter circuitry correspond to
terms used on the schematic diagrams in Section 5.
SPECIFICATIONS 1-4.
Specifications for the meters are presented in Table 1-1.
1-4

Introduction and Specifications
SPECIFICATIONS
Table 1-1. Specifications
Maximum Voltage Between any
Terminal and Earth Ground 1000V dc, 750V ac rms (sine)
Fuse Protection 300 mA: 630 mA, 250V Fast Fuse
10A: 15A, 600V FAST Fuse
Display Digital: 3,200 counts, updates 2.5/sec
Analog: 32 segments, updates 25/sec
Response Time of Digital Dis-
play to Rated Accuracy Vac <2s
Vdc <1s
n<1sto 320 k£2, <2sto 3.2 M£2, <10 sto 32 M
Operating Temperature 0*C to 50'C
Storage Temperature -40‘C to 60*
C
Temperature Coefficient 0.1 x(specified accuracy)/*C
(<18*C or >28*C)
Relative Humidity 0% to 90% (0*C to 35*C)
Except 32 Mfi Range: 0% to 70% (35’C to 50* C)
0% to 80% (0*C to 35’C)
32 M£2 Range Only: 0% to 70% (35‘C to 50*C)
Battery Type 9V, NEDA 1604 or 6F22 or 006P
Battery Life 2000 hrs typical with alkaline
1600 hrs typical with carbon zinc
Continuity Beeper 4096 Hz
Shock, Vibration Per MIL-T-28800 for aStyle B, Class 2Instrument
Size (HxWxL) 2.8 cm x7.5 cm x16.6 cm
(1.12 in x2.95 in x6.55 in)
Weight 340g (12 oz)
Safety Designed to Protection Class II per IEC 348, ANSI/ISA-S82,
UL1244, and CSA C22.2 No.231
1-5

Introduction and Specifications
SPECIFICATIONS
Table 1-1. Specifications (cont)
FUNCTION RANGE RESOLUTION
VAC 3.200V 0.001V
(45-500 Hz, 3.2Vrng 32.00V 0.01V
Other ranges 45-1 kHz) 320.0V 0.1V
750V IV
o320.00 0.10
3200 o1o
32.00 kO 0.01 kO
320.0 kO 0.1 kO
3.200 MO 0.001 MO
32.00 MO 0.01 MO
-H- '«!) 2.0V 0.001V
AAC* 32.00 mA** 0.01 mA
(45 Hz to 1kHz) 320 mA** 0.1 mA
10.00 A*** 0.01 A
ADC* 32.00 mA** 0.01 mA
320 mA** 0.1 mA
10.00 A*** 0.01A
*Current function not available on Fluke 70
** Ranges available on Fluke 75/21 and 77/23 only.
*** 10A continuous, 20A for 30 seconds maximum
BURDEN
VOLTAGE
(TYPICAL)
Not Applicable
FUNCTION RESOLUTION ACCURACY
70 73/75/21 77/23
0.001V ±(0.5%+1
)
+(0.4%+1) ±(0.3%+1)
0.01V ±(0.5%+1) ±(0.4%+1
)
±(0.3%+1)
0.1V ±(0.5%+1) ±(0.4%+1) ±(0.3%+1
)
IV ±(0.6%+1) ±(0.4%+1
)
±(0.4%+1)
0.1 mV ±(0.5%+1) ±(0.4%+1
)
±(0.3%+1
)

Introduction and Specifications
SPECIFICATIONS

Introduction and Specifications
SPECIFICATIONS

Section 2
Theory of Operation
CONTENTS PAGE
2-1. INTRODUCTION 2-3
2-2. FUNCTIONAL BLOCK DESCRIPTION 2-3
2-3. DETAILED DESCRIPTION 2-3
2-4. Voltage Signal Conditioning 2-3
2-5. Current Conditioning 2-4
2-6. Ohms 2-4
2-7. Additional Circuitry 2-4
2-8. AC CONVERTER 2-4
2-9. ACTIVE FILTER 24
2-10. ROTARY SWITCH 2-5
2-11. A/D CONVERSION 2-5
2-1

Theory of Operation
2-2

Theory of Operation
INTRODUCTION
INTRODUCTION 2-1.
This section contains abrief overview of the 70, 73, 75, 77, 21, and 23 Series II
Multimeters, followed by amore detailed explanation of operation.
FUNCTIONAL BLOCK DESCRIPTION 2-2.
The heart of the instrument consists of atwo-chip CMOS system: Ul, aprimarily
analog IC, and U2, acalculator-style microcomputer (see Figure 2-1).
The analog chip, Ul, contains the a/d converter, active filter, ac converter, analog signal
routing, range switching, and power supply functions. Peripherals to Ul include
function switching, voltage reference, and the crystal.
The microcomputer, U2, controls the a/d converter function and range switching, reads
and formats the a/d samples, and drives the liquid crystal display (LCD).
DETAILED DESCRIPTION 2-3.
The following paragraphs describe the 70, 73, 75, 77, 21 and 23 Series II multimeters in
more detail. While reading this description, refer to the schematic diagram in Section 5.
Voltage Signal Conditioning 2-4.
Input divider Z1 and dc blocking capacitor Cl make up an input voltage signal
conditioning circuit.
Figure 2-1. Overview
2-3

Theory of Operation
DETAILED DESCRIPTION
The pins of Z1 are used as follows:
Z1-PIN NUMBER FUNCTION
1input
33.2V range tap
432V range tap
5320V range tap
61000V dc/750V ac range tap
Overvoltage protection is provided by El, Rl, R2, RV1, and RV2.
El is aspark gap that fires between 1200V and 1800V. Rl is afusible resistor that
opens with excessive inputs. RV1 and RV2 are metal-oxide varistors that clamp around
910V each.
Current Conditioning 2-5.
Current input conditioning is provided by R6, R7, R5, and R13. R6 and R7 develop
input voltage from the applied current. R5 and R13 act as avoltage divider for the
300-mA range. FI protects the mA circuitry; F3 protects the 10A circuitry. (Model 70
has no current-measuring capability; Model 73 measures current only on the 10A
range.)
Ohms 2-6.
When the ohms function is selected, the meter compares the unknown resistance at J1
with the reference resistors in Zl. (See Figure 2-2, Ohms Function.)
Input protection for the ohms ranges consists of Ql, Q2, Q3, R2, R3, R4, and RT1. Q1
and Q2 serve as back-to-back zener diodes which limit the input to between 7and 9V.
RT1 is athermistor that normally has about 1kfl of resistance but increases to very
high impedance as it heats up with an overload voltage. Also, R2, R3, and R4 limit
current, and Q3 clamps pin 29 of U1 to approximately 2.5V.
Additional Circuitry 2-7.
In addition to the above circuitry, the following circuitry is also used in the Series II
meters: AC Converter, Active Filter, Rotary Switch, and A/D Conversion.
AC CONVERTER 2-8.
The ratio of R17 and R18 determines ac voltage and current accuracy (see Figure 2-3,
AC and A/D Converter), and Cll is the averaging capacitor for the half-wave ac
converter portion of Ul.
ACTIVE FILTER 2-9.
An active filter that includes R9, R10, C5, and C6 is located in Ul. Conditioned input
signals are passed through the active filter in route to the a/d converter section of Ul.
(See Figure 2-3, AC and A/D Converter.)
2-4
The clock frequency for the digital portion of the circuit is afunction of 32.768-kHz
crystal Yl. Yl, C12, C15, and amplifiers in Ul make up the oscillator circuit.