Fluke 77 III Service Manual

®

77 Series III

Multimeter

Service Manual

PN 800604
November 1998 Rev.1, 11/99

© 1998,1999 Fluke Corporation. All rights reserved. Printed in U.S.A.
All product names are trademarks of their respective companies.

Table of Contents

Chapter Title Page

1 Introduction 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

2 Theory 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. Current Conditioning .............................................. 2-4

2-6. Ohms ....................................................................... 2-4

2-7. Additional Circuitry ................................................ 2-4

2-8. AC Converter ..................................................... 2-5

2-9. Active Filter ....................................................... 2-5

2-10. Rotary Switch ..................................................... 2-5

2-11. A/D Conversion .................................................. 2-5

3 Maintenance ................................................................ 3-1

3-1. Introduction ................................................................. 3-3

3-2. PCA Access and General Maintenance ...................... 3-3

3-3. Display Access ............................................................ 3-4

3-4. Cleaning ...................................................................... 3-4

3-5. Performance Test ........................................................ 3-7

3-6. Initial Procedure ..................................................... 3-7

3-7. DC Voltage Test ..................................................... 3-7

3-8. AC Voltage Test ......................................................... 3-8

3-9. Resistance Test ....................................................... 3-8

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77 Series III

Service Manual

3-10. Diode Test .............................................................. 3-9

3-11. DC mA Test ............................................................ 3-10

3-12. DC Amps Test ........................................................ 3-11

3-13. Calibration .............................................................. 3-11

3-14. Troubleshooting .......................................................... 3-11

3-15. Supplemental Troubleshooting Procedures ............ 3-13

3-16. Checking the Crystal Oscillator ......................... 3-13

3-17. Checking The Reference Voltage ...................... 3-13

3-18. Checking Display Drive Voltage ....................... 3-13

3-19. Checking Beeper Drive Signal ........................... 3-13

3-20. Tracing the VDC Signal Path ............................. 3-13

4 List of Replaceable Parts............................................ 4-1

4-1. Introduction ................................................................. 4-3

4-2. How to Obtain Parts .................................................... 4-3

4-3. Newer Instruments ...................................................... 4-3

4-4. Service Centers ........................................................... 4-3

4-5. Manual Status Information ......................................... 4-4

4-6. Parts Lists .................................................................... 4-4

5 Schematic Diagrams................................................... 5-1

ii

List of Tables

Table Title Page

1-1. Specifications ..................................................................... 1-5

2-1. S1 Function Codes.............................................................. 2-6

3-1. Recommended Test Equipment.......................................... 3-3

3-2. DC Voltage Test................................................................. 3-8

3-3. AC Voltage Test................................................................. 3-8

3-4. Resistance Test................................................................... 3-10

3-5. DC mA Test........................................................................ 3-11

3-6. DC Amps Test.................................................................... 3-11

4-1. Final Assembly................................................................... 4-5

4-2. A1 Main PCA..................................................................... 4-7

5-1. Abbreviations ..................................................................... 5-3

iii

77 Series III

Service Manual

iv

List of Figures

Figure Title Page

2-1. Overview ............................................................................ 2-3

2-2. AC and A/D Converter....................................................... 2-7

3-1. Assembly Details................................................................ 3-6

3-2. Troubleshooting Tree......................................................... 3-12

4-2. A1 Main PCA..................................................................... 4-9

5-1. A1 Main PCA..................................................................... 5-4

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77 Series III

Service Manual

vi

OPERATOR SAFETY

INFORMATION

This instrument has been designed and tested in accordance with IEC
Publication 348, Safety Requirements for Electronic Measuring Apparatus. This
manual contains information and warnings which have to be followed by the
user to ensure safe operation and to retain the instrument in safe condition.

Warning statements identify conditions or practices that could result in
personal injury or loss of life.

Caution statements identify conditions or practices that could result in damage
to the equipment or other property.

•

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 a circuit when power is applied to the circuit.

•

Never touch the probes to a voltage source when the test leads are

plugged into the 10A or 300 mA input jack.

•

Never apply more than 1000V dc or 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.

SAFETY-1

Symbols Marked on Equipment

DANGER — High Voltage
Attention — refer to the manual. This symbol indicates that

information about the usage of a feature is contained in the

l.

manua

I Fuse information

Use the Proper Fuse

To avoid fire hazard, use only the fuse identical in type, voltage
rating, and current rating as specified on the case bottom fuse rating
label.

Do Not Remove Cover

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 is doubt, have the
instrument serviced.

SAFETY-2

Chapter 1

Introduction and

Specifications

Contents Page

1-1. Introduction.................................................................. 1-3

1-2. Organization of the Service Manual............................ 1-3

1-3. Conventions ................................................................. 1-4

1-4. Specifications............................................................... 1-4

1-1

77 Series III

Service Manual

1-2

Introduction and Specifications

Introduction

1-1. Introduction

This manual presents service information for the Fluke 77 Series III
Multimeter. The manual includes a theory of operation, general maintenance
procedures, performance tests, calibration procedures, troubleshooting
information, a list of replaceable parts, and schematic diagrams.

A meter under warranty will be promptly repaired or replaced (at Fluke’s
option) and returned at no charge. See the registration card for warranty terms.
To locate an authorized service center, visit us on the World Wide Web:
www.fluke.com or call using any of the phone numbers listed below:

USA: 1-888-99-FLUKE (1-888-993-5853)
Canada: 1-800-36-FLUKE (1-800-363-5853)
Europe: [phone]
Japan: [phone]
Singapore: [phone]
Anywhere in the world: [phone]

1-2. Organization of the Service Manual

The following descriptions briefly describe each chapter in the manual.

1

Chapter 1 Introduction and Specifications
This chapter describes use of the Service Manual and application of special

terminology (conventions) to describe the meter’s circuitry. A complete set of
specifications appears at the end of this chapter.

Chapter 2 Theory of Operation
This chapter first categorizes instrument circuitry into functional blocks, with

a description of each block’s role in overall operation. A detailed 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.

Chapter 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 Chapter 2 and the Schematic Diagrams
shown in Section 5.

Chapter 4 List of Replaceable Parts
Includes parts lists for all standard assemblies. Information on how and where

to order parts is also provided.
Chapter 5 Schematic Diagrams

Includes schematic for the A1 Main PCA.

1-3

77 Series III

Service Manual

1-3. Conventions

Through the manual, certain notational conventions are used. A summary of
these conventions follow:

• Instrument Reference

The Fluke 77 Series III Multimeter is also referred to throughout this

manual as “the meter”.

• Printed Circuit Assembly

The term “pca” is used to represent a printed wiring board and its

attached parts.

• Circuit Nodes

Individual pins or connections on a component are specified by a dash

(-) 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 Chapter 5.

1-4. Specifications

Specifications for the meters are presented in Table 1-1.

1-4

Introduction and Specifications

Table 1-1. Specifications

Specifications

1

Maximum Voltage Between any
Terminal and Earth Ground

Display Digital: 3,200 counts, updates 2.5/sec

Response Time of Digital Display V ac < 2 s

Operating Temperature 0°C to 50°C
Storage Temperature -40°C to 60°C
Temperature Coefficient 0.1 x (specified accuracy)/°C

Electromagnetic Compatibility In
RF field of 3 V/m on all functions.

Relative Humidity

except 32 MΩ range
32 MΩ range only

Altitude Operating: 2000 meters

Battery Type 9 V NEDA 1604 or 6F22 or 006P,

Battery Life 2000 hrs typical with alkaline

Continuity Beeper 4096 Hz
Shock, Vibration per MIL-T-PRF 28800F Class III, Sinusoidal,

Size (H x W x L) 3.7 cm x 8.9 - 7.8 cm x 19 cm

Weight 365 g (12.9 oz)
Safety 600 V CAT III and 1000 V CAT II per

EMC Regulations EN 61326-1 1997.
Certifications/Listings

Rated voltage

Analog: 31 segments, updates 25/sec

V dc < 1 s
Ω < 1s to 320 kΩ, < 2s to 3.2 MΩ,
< 10 s to 32 MΩ

(<18°C or >28°C)
Total accuracy = Specified accuracy

+ 0.1% of range.

0% to 90% (0°C to 35°C)
0% to 70% (35°C to 50°C)
0% to 80% (0°C to 35°C)
0% to 70% (35°C to 50°C)

Storage: 12,000 meters

or NEDA 1604A or 6LR61

1600 hrs typical with carbon zinc

Non Operating

(1.5 in x 3.5 - 3.1 in x 7.49 in)

ANSI/ISA S82.01-1994, EN 61010-1: 1993,
CSA C22.2 No 1010.1-92, UL 3111-1.

1-5

77 Series III

Service Manual

Table 1-1. Specifications (cont)

Function Range Accuracy

L

L

m

K (45 to 500 Hz,

3.2 V range. Other
ranges 45 to 1
kHz)

e

G R 2.0 V ±(1% typical)

Function Range Accuracy Burden Voltage

? (45 Hz to 1 kHz)

A

* 10 A continuous, 20 A for 30 seconds maximum.

3.200 V

32.00 V

320.0 V
1000 V

320.0 mV ±(0.3%+1)

3.200 V

32.00 V

320.0 V
1000 V

320.0 Ω
3200 Ω

32.00 kΩ

320.0 kΩ

3.200 MΩ

32.00 MΩ

32.00 mA,

320.0 mA

10.00 A *

32.00 mA,

320.0 mA

10.00 A *

±(2.5%+2)
±(2.5%+2)

±(1.5%+2)
±(1.5%+2)

±(0.3%+1)
±(0.3%+1)
±(0.3%+1)
±(0.4%+1)

±(2%+2)
±(2%+2)
±(2%+2)
±(2%+2)

±(0.5%+3)
±(0.5%+1)
±(0.5%+1)
±(0.5%+1)
±(0.5%+1)
±(2.0%+1)

(typical)

6 mV/mA
50 mV/A

6 mV/mA
50 mV/A

1-6

Introduction and Specifications

Overload protection for all functions and ranges: Rated voltage.

Function Input Impedance (Nominal)

L, mL, K

L,

L

m

K

e

G R

e

G R

G

>10 MΩ, <50 pF

Common Mode Rejection
Ratio (1 kΩ Unbalanced)

>120 dB at dc, 50 Hz, or 60 Hz >60 dB at 50 Hz or 60 Hz
>60 dB dc to 60 Hz

Open Circuit Test Voltage Full Scale Voltage

<3.1 V dc
<2.8 V dc (typical)

Open Circuit Test Voltage Full Scale Voltage

<3.1 V dc 2.0 V dc

Short Circuit Current (typical)

300 µA
400 µA

V

F

0.0 V

0.6 V

1.2 V

2.0 V

Normal Mode Rejection

To 3.2 MΩ 32 MΩ

<440 mV dc
<420 mV dc
(typical)

Current (typical)

0.4 mA

0.3 mA

0.2 mA

0.1 mA

Specifications

<1.4 V dc
<1.3 V dc
(typical)

1

1-7

77 Series III

Service Manual

1-8

Chapter 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 ........................................................ 2-5

2-10. Rotary Switch...................................................... 2-5

2-11. A/D Conversion................................................... 2-5

2-1