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Fluke 77 Series III Service Manual

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®
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.

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  Summary of Contents for Fluke 77 Series III

  • Page 1: 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.
  • Page 2: Table Of Contents

    Table of Contents Chapter Title Page 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 Theory of Operation ............ 2-1 2-1. Introduction ..............2-3 2-2.
  • Page 3 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.
  • Page 4 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.
  • Page 5 77 Series III Service Manual...
  • Page 6 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...
  • Page 7 77 Series III Service Manual...
  • Page 8 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.
  • Page 9 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 manua 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.
  • Page 10: Introduction And Specifications

    Chapter 1 Introduction and Specifications Contents Page 1-1. Introduction..............1-2. Organization of the Service Manual ......1-3. Conventions ..............1-4. Specifications...............
  • Page 11 77 Series III Service Manual...
  • Page 12: Introduction

    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.
  • Page 13: 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.
  • Page 14 Introduction and Specifications 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 <...
  • Page 15 77 Series III Service Manual Table 1-1. Specifications (cont) Function Range Accuracy 3.200 V (0.3%+1) 32.00 V (0.3%+1) 320.0 V (0.3%+1) 1000 V (0.4%+1) 320.0 mV (0.3%+1) 3.200 V (2%+2) (45 to 500 Hz, 32.00 V (2%+2) 3.2 V range. Other 320.0 V (2%+2) ranges 45 to 1...
  • Page 16 Introduction and Specifications Specifications Overload protection for all functions and ranges: Rated voltage. Function Input Impedance (Nominal) , m , >10 M , <50 pF Common Mode Rejection Normal Mode Rejection Ratio (1 k 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...
  • Page 17 77 Series III Service Manual...
  • Page 18: Theory Of Operation

    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.
  • Page 19 77 Series III Service Manual...
  • Page 20: Introduction

    Theory of Operation Introduction 2-1. Introduction This chapter contains a brief overview of the 77 Series III Multimeter, followed by a more detailed explanation of operation. 2-2. Functional Block Description The heart of the instrument consists of a two-chip CMOS system: U1, a primarily analog IC, and U2, a calculator-style microcomputer (see Figure 2- Input Signal...
  • Page 21: Current Conditioning

    77 Series III Service Manual The pins of Z1 are used as follows: Z1-PIN NUMBER FUNCTION input 3.2V range tap 32V range tap 320V range tap 1000V dc/750V ac range tap Overvoltage protection is provided by R1, RV1, RV2, RV3, and RT1. RT1 is a thermistor that normally has about 1 k of resistance, but increases to very high impedance as it heats up with an overload voltage.
  • Page 22: Active Filter

    Theory of Operation Detailed Description 2-9. Active Filter An active filter that includes R9, R10, C5, and C6 is located in U1. Conditioned input signals are passed through the active filter in route to the a/d converter section of U1. (See Figure 2-2, AC and A/D Converter.) The clock frequency for the digital portion of the circuit is a function of 32.768-kHz crystal Y1.
  • Page 23: S1 Function Codes

    77 Series III Service Manual Conditioned input signals are routed to the a/d converter in U1, where they are integrated. The reference voltage developed by reference supply VR1, R15, R16, and R8 is routed to the a/d converter in U1, where it is used for the integrate reference (de-integrate) portions of the measurement cycle.
  • Page 24 Theory of Operation Detailed Description aaa03f.eps Figure 2-2. AC and A/D Converter...
  • Page 25 77 Series III Service Manual...
  • Page 26: Maintenance

    Chapter 3 Maintenance Contents Page 3-1. Introduction..............3-2. PCA Access and General Maintenance ......3-3. Display Access..............3-4. Cleaning ................3-5. Performance Test ............3-6. Initial Procedure ............3-7. DC Voltage Test ............3-8. AC Voltage Test ............. 3-9. Resistance Test ............3-10.
  • Page 27 77 Series III Service Manual...
  • Page 28: Introduction

    Table 3-1. Recommended Test Equipment Instrument Type Recommended Model Multi-Product Calibrator Fluke 5500A 3-2. PCA Access and General Maintenance Warning To avoid electrical shock, remove the test leads before opening the case, and close the case before operating the meter.
  • Page 29: Display Access

    77 Series III Service Manual 1. Set the function switch to OFF, and disconnect test leads if they are installed. 2. Remove the four Phillips screws from the bottom cover. 3. Turn the meter face up, grasp the top cover, and pull the top cover from the meter.
  • Page 30 Maintenance Cleaning Clean the instrument case with a mild detergent and water. The pca may be washed with isopropyl alcohol or deionized water and a soft brush. Remove the display assembly and fuses before washing, and avoid washing the switch if possible. Dry the pca with clean dry air at low pressure, then bake it at 50 C for 24 hours.
  • Page 31 Shock Absorber Detent Spring Elastomeric Connector Key Pad Internal Cover Shaft Adapter AC Shield Main PCA Screw, 4-24 Screw, 4-14 Bottom Shield Case Bottom Assembly Battery Annunciator Screw, 5-14 Contact Probe Holder Tilt Stand FLUKE-77-3 aaa12c.eps Figure 3-1. Assembly Details...
  • Page 32: Performance Test

    Instruction Sheet. If the instrument fails any part of the test, calibration and/or repair is indicated. In the performance tests, the Fluke 77 Series III is referred to as the unit under test (UUT).
  • Page 33: Dc Voltage Test

    77 Series III Service Manual Table 3-2. DC Voltage Test Step DC Input Voltage Display Reading +2.7V 2.691 to 2.709V DC +27V 26.91 to 27.09V DC +270V 269.1 to 270.9V DC +1000V 995 to 1005V DC +300 mV 299.0 to 301.0V DC *300 mV function only 3-8.
  • Page 34: Diode Test

    1. Set the UUT to the Diode Test function. Note On Fluke 5100 series calibrators, activate the 50 divider override. On Fluke 5500A calibrators, lock voltage to the 33V range. 2. Apply an input from the DC Voltage Calibrator of +.090V dc to the and COM input terminals of the UUT, and verify that the beeper is on.
  • Page 35: Dc Ma Test

    77 Series III Service Manual Table 3-4. Resistance Test Step Input Resistance Display Reading short 0.0 to 0.3 Decades of 1: 99.2 to 100.8 (plus 0 reading) 994 to 1006 10 k 9.94 to 10.06 k 100 k 99.4 to 100.6 k .994 to 1.006 M 10 M 9.79 to 10.21 M...
  • Page 36: Dc Amps Test

    Maintenance Troubleshooting Table 3-5. DC mA Test Step Input Current Display Reading +27 mA 26.57 to 27.43 DC +200 mA 196.8 TO 203.2 DC 3-12. DC Amps Test 1. Set the DC Current Calibrator to standby and connect it to the 10A and COM input terminals of the UUT.
  • Page 37 77 Series III Service Manual Turn meter on Check: Does meter power up? a. Power supplies TP1 = 3.1V dc +/-0.1V TP3 = 1.5V dc U1 pin 48 = 6V dc (Battery voltage - TPIV) (If any of these voltages are high, low, or missing, replacement of U1 is usually necessary) b.
  • Page 38: Supplemental Troubleshooting Procedures

    Maintenance Troubleshooting 3-15. Supplemental Troubleshooting Procedures 3-16. Checking the Crystal Oscillator Connect an oscilloscope or counter to pin 54 U1 or to the junction of C12 and the Y1 crystal. Check for a 32.768-kHz sine wave approximately 600 mV p-p in amplitude.
  • Page 39 77 Series III Service Manual 3-14...
  • Page 40 A Message From Fluke Corporation Some semiconductors and custom IC's can be damaged by electrostatic discharge during handling. This notice explains how you can minimize the chances of destroying such devices 1. Knowing that there is a problem.
  • Page 41 8. WHEN REMOVING PLUG-IN ASSEMBLIES 5. USE STATIC SHIELDING CONTAINERS FOR HANDLE ONLY BY NON-CONDUCTIVE HANDLING AND TRANSPORT. EDGES AND NEVER TOUCH OPEN EDGE CONNECTOR EXCEPT AT STATIC-FREE WORK STATION. PLACING SHORTING STRIPS ON EDGE CONNECTOR HELPS PROTECT INSTALLED S.S. DEVICES. 6.
  • Page 42: List Of Replaceable Parts

    Chapter 4 List of Replaceable Parts Contents Page 4-1. Introduction..............4-2. How to Obtain Parts............4-3. Newer Instruments ............4-4. Service Centers ............... 4-5. Manual Status Information ..........4-6. Parts Lists................
  • Page 43 77 Series III Service Manual...
  • Page 44: Introduction

    Electrical components may be ordered directly from the Fluke Corporation and its authorized representatives by using the part number under the heading FLUKE PN. In the U.S., order directly from the Fluke Parts Dept. by calling 1-800-526-4731. Parts price information is available from the Fluke Corporation or its representatives.
  • Page 45: Manual Status Information

    This instrument may contain a Nickel-Cadmium battery. Do not mix with the solid waste stream. Spent batteries should be disposed of by a qualified recycler or hazardous materials handler. Contact your authorized Fluke service center for recycling information. Warning This instrument contains a fusible resistor (pn 740662).
  • Page 46: Final Assembly

    MASK,BRACKET,77-3 WITH LOGO 648771 MP21 CONN,ELASTOMERIC,LCD TO PWB,1.900 L 650264 MP23 SHIELD,BOTTOM 648839 MP32 TEST LEADS TL75 MP40 CONTACT,ANNUNCIATOR 642983 KEYPAD 648847 77/75/23/21 SERIES III INSTRUCTION 686571 SHEET 77 SERIES III SERVICE MANUAL 800604 W To ensure safety, use exact replacement only.
  • Page 47 77 Series III Service Manual MP11 MP17 MP18 MP20 MP16 MP10 MP21 MP19 MP12 MP23 MP14 MP40 FLUKE-77-3 aaa05c.eps Figure 4-1. Final Assembly...
  • Page 48: A1 Main Pca

    List of Replaceable Parts Parts Lists Table 4-2. A1 Main PCA Ref Des Description Qty. Notes CAP,POLYES,0.0UF, 10%,1000V 822361 C2,C3 CAP,CER,0.1UF, 10%,25v,X7R 942529 CAP,TA,2.2UF, 20%,20V 854760 C5,C6 CAP,POLYCA,0.027UF, 10%,63V 720979 CAP,TA,0.47UF, 20%,25V 876180 CAP,POLYPR,0.033UF, 10%,63V 721050 CAP,TA,10UF, 20%,10V,3528 603032 CAP,CER,0.1UF, 10%,25V,XR7 942529 CAP,TA,2.2UF, 20%,6V,3216 930248...
  • Page 49 77 Series III Service Manual Table 4-2. A1 Main PCA (cont) Ref Des Description Qty. Notes CONTACT, FUSE 707190 CRYSTAL,32.768KHZ, +-1%,3 X 8MM 643031 * RNET,CERM,SIP,FLUKE 77 HI V DIV. 946202 * RNET,CERM,SIP, HI V PROTECT 103454...
  • Page 50 List of Replaceable Parts Parts Lists FLUKE 77-3-4001 aaa06f.eps Figure 4-2. A1 Main PCA...
  • Page 51 77 Series III Service Manual FLUKE 77-3-4001 aaa07f.eps Figure 4-2. A1 Main PCA (cont.) 4-10...
  • Page 52: Schematic Diagrams

    Chapter 5 Schematic Diagrams...
  • Page 53 77 Series III Service Manual...
  • Page 54: Abbreviations

    Schematic Diagrams Table 5-1. Abbreviations Abbreviation Definition AC Converter Feedback ACHI AC Converter High All Clear, Reset ACLO AC Converter Low Active Filter Input Active Filter Output Amp[s Input Amps Divide by 10 Auto Zero Point Beeper Driver Battery Clock Output Common DC Sense Reference Voltage...
  • Page 55 77 Series III Service Manual FLUKE 77-3-4001 aaa06f.eps Figure 5-1. A1 Main PCA...
  • Page 56 Schematic Diagrams FLUKE 77-3-4001 aaa07f.eps Figure. A1 Main PCA (cont)
  • Page 57 C O M M O N C O M V D D REFERENCE DESIGNATON 61.9K LAST NOT USED USED C R 2 C R 2 BAS16 56.2K 0.1W 1.23V 205K 0.1W 2.7V 100K 2 5 % FLUKE 77-3-1001 aaa09f.eps Figure 5-1. A1 Main PCA (cont)
  • Page 58 1000V,300 NDAV DT,OHMS O H M S DE-INT MA,10A DE-INT RANGE DIGITAL SECTION ACTIVE CONVERTER FILTER BUFFER INTEGRATOR L O W FILTER* HIGH 0.47 .033 1.50M 0.1W .027 .027 9.20K 0.5% FLUKE 77-3-1001 aaa10f.eps Figure 5-1. A1 Main PCA (cont)
  • Page 59 DESIGNATES WIRE WOUND RESISTOR DESIGNATES METAL GLAZE RESISTOR AC VOLTS DESIGNATES METAL FILM RESISTOR DC VOLTS CERM DESIGNATES CERMET FILM RESISTOR 300 MVDC OHMS DIODE TEST/CONTINUITY AC CURRENT DC CURRENT *1=VDD 0=COMMON FLUKE 77-3-1001 aaa11f.eps Figure 5-1. A1 Main PCA (cont)