Fluke 77 Series III User 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.

i
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

77 Series III
Service Manual
ii
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

iii
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

77 Series III
Service Manual
iv

v
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

77 Series III
Service Manual
vi

SAFETY-1
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-2
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.

1-1
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