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

i

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

v

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 manual.

IFuse 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	1
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.

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		1
		Specifications
	Table 1-1. Specifications
	Maximum Voltage Between any	Rated voltage
	Terminal and Earth Ground
	Display	Digital: 3,200 counts, updates 2.5/sec
		Analog: 31 segments, updates 25/sec
	Response Time of Digital Display	V ac < 2 s
		V dc < 1 s
		Ω < 1s to 320 kΩ, < 2s to 3.2 MΩ,
		< 10 s to 32 MΩ
	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)
	Electromagnetic Compatibility In	Total accuracy = Specified accuracy
	RF field of 3 V/m on all functions.	+ 0.1% of range.
	Relative Humidity
	except 32 MΩ range	0% to 90% (0°C to 35°C)
	32 MΩ range only	0% to 70% (35°C to 50°C)
		0% to 80% (0°C to 35°C)
		0% to 70% (35°C to 50°C)
	Altitude	Operating: 2000 meters
		Storage: 12,000 meters
	Battery Type	9 V NEDA 1604 or 6F22 or 006P,
		or NEDA 1604A or 6LR61
	Battery Life	2000 hrs typical with alkaline
		1600 hrs typical with carbon zinc
	Continuity Beeper	4096 Hz
	Shock, Vibration	per MIL-T-PRF 28800F Class III, Sinusoidal,
		Non Operating
	Size (H x W x L)	3.7 cm x 8.9 - 7.8 cm x 19 cm
		(1.5 in x 3.5 - 3.1 in x 7.49 in)
	Weight	365 g (12.9 oz)
	Safety	600 V CAT III and 1000 V CAT II per
		ANSI/ISA S82.01-1994, EN 61010-1: 1993,
		CSA C22.2 No 1010.1-92, UL 3111-1.
	EMC Regulations	EN 61326-1 1997.
	Certifications/Listings

1-5

77 Series III

Service Manual

			Table 1-1. Specifications (cont)
	Function		Range				Accuracy
	L		3.200	V			±(0.3%+1)
			32.00	V			±(0.3%+1)
			320.0	V			±(0.3%+1)
			1000 V				±(0.4%+1)
	mL		320.0 mV				±(0.3%+1)
	K (45 to 500 Hz,		3.200	V			±(2%+2)
	3.2 V range. Other		32.00	V			±(2%+2)
	ranges 45 to 1		320.0	V			±(2%+2)
	kHz)		1000 V				±(2%+2)
	e		320.0	Ω			±(0.5%+3)
			3200 Ω				±(0.5%+1)
			32.00 kΩ				±(0.5%+1)
			320.0 kΩ				±(0.5%+1)
			3.200	MΩ			±(0.5%+1)
			32.00	MΩ			±(2.0%+1)
	G R		2.0 V				±(1% typical)
	Function		Range			Accuracy		Burden Voltage
								(typical)
	? (45 Hz to 1 kHz)		32.00 mA,			±(2.5%+2)		6 mV/mA
			320.0 mA		±(2.5%+2)			50 mV/A
			10.00	A *
	A		32.00 mA,			±(1.5%+2)		6 mV/mA
			320.0 mA		±(1.5%+2)			50 mV/A

10.00A *

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

1-6

Introduction and Specifications	1
Specifications

Overload protection for all functions and ranges: Rated voltage.

Function	Input Impedance (Nominal)
L, mL, K	>10 MΩ, <50 pF
	Common Mode Rejection					Normal Mode Rejection
	Ratio (1 kΩ Unbalanced)
L, mL	>120 dB at dc, 50 Hz, or 60 Hz					>60 dB at 50 Hz or 60 Hz
K	>60 dB dc to 60 Hz
	Open Circuit Test Voltage					Full Scale Voltage
						To 3.2 MΩ		32 MΩ
e	<3.1 V dc					<440 mV dc		<1.4 V dc
	<2.8 V dc (typical)					<420 mV dc		<1.3 V dc
						(typical)		(typical)
	Open Circuit Test Voltage					Full Scale Voltage
G R	<3.1 V dc						2.0 V dc
		Short Circuit Current (typical)
e			300 μA
G R			400 μA
G	VF					Current (typical)
	0.0	V				0.4 mA
	0.6	V				0.3 mA
	1.2	V				0.2 mA
	2.0	V				0.1 mA

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