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Ž

Automotive Meter

78

Service Manual
For IEC 61010 CAT II Meters Only

PN 666617 November 1998
Š 1998 Fluke Corporation, All rights reserved. Printed in U.S.A. All product names are trademarks of their respective companies.

LIMITED WARRANTY & LIMITATION OF LIABILITY Fluke Corporation (Fluke) warrants this product to be free from defects in material and workmanship under normal use and service for the life of the product. This warranty extends only to the original buyer or end-user customer of a Fluke authorized reseller, and does not apply to fuses, batteries or to any product which, in Fluke's opinion, has been misused, altered, neglected or damaged by accident or abnormal conditions of operation or handling. Fluke warrants that software will operate on appropriate Fluke instruments substantially in accordance with its functional specifications for 90 days and that it has been properly recorded on non-defective media. Fluke does not warrant that software will be error free or operate without interruption. Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers only but have no authority to extend a greater or different warranty on behalf of Fluke. Fluke's warranty obligation is limited, at Fluke's option, to refund of the purchase price, or free of charge repair or replacement of a defective product which is returned to an authorized Fluke Service Center within the warranty period. To obtain warranty service, contact your nearest Fluke Service Center or send the product, with a description of the difficulty, postage and insurance prepaid (FCA Destination), to the nearest Fluke Service Center. Fluke assumes no risk for damage in transit. Following warranty repair, the product will be returned to Buyer, transportation prepaid (FCA Destination). If Fluke determines that the failure was caused by misuse, alteration, accident or abnormal condition of operation or handling, Fluke will provide an estimate of repair costs and obtain authorization before commencing the work. Following repair, the product will be returned to the Buyer transportation prepaid and the Buyer will be billed for the repair and return transportation charges (FCA Shipping Point). Warranty service is available outside the United States only if product was purchased through a Fluke Authorized Sales Outlet in the country of use or the applicable Fluke international price was paid. Product transported from the United States for which the applicable Fluke international price was not paid must be returned to the U.S. to receive warranty service, at the shipment expense and risk of Buyer. Fluke reserves the right to invoice Buyer for importation costs of repair/replacement parts when product purchased in one country is submitted for repair in another country. THIS WARRANTY IS PURCHASER'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. FLUKE SHALL NOT BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSSES, INCLUDING LOSS OF DATA, WHETHER ARISING FROM BREACH OF WARRANTY OR BASED ON CONTRACT, TORT, RELIANCE OR ANY OTHER THEORY. Since some countries or states do not allow limitation of the term of an implied warranty, or exclusion or limitation of incidental or consequential damages, the limitations and exclusions of this warranty may not apply to every buyer. If any provision of this Warranty is held invalid or unenforceable by a court of competent jurisdiction, such holding will not affect the validity or enforceability of any other provision of this warranty. Fluke Corporation P.O. Box 9090 Everett WA 98206-9090 Fluke Europe B.V. P.O. Box 1186 5602 B.D. Eindhoven The Netherlands

Safety Information
This meter complies with EN 61010-1:1993, ANSI/ISA S82.01-1994 and CAN/CSA C22.2 No. 1010.1-92 Overvoltage Category II. Use the meter only as specified in the Users Manual, otherwise the protection provided by the meter may be impaired. A Warning identifies conditions and actions that pose hazards to the user; a Caution identifies conditions and actions that might damage the meter. International electrical symbols used on the meter are shown below.

W Warning
To avoid possible electric shock or personal injury: ˇ Do not use the meter if it is damaged. Before use, inspect the case for cracks or missing plastic. Pay particular attention to the insulation surrounding the connectors. Always turn off power to the circuit before cutting, unsoldering, or breaking the circuit. Small amounts of current can be dangerous. Inspect the test leads for damaged insulation or exposed metal. Check test lead continuity. Replace damaged leads. To avoid damage or injury, never use the meter on unprotected circuits that exceed 4800 volt-amps. Do not use the meter if it operates abnormally. Protection may be impaired. When in doubt, have the meter serviced. Do not operate the meter around explosive gas, vapor or dust. Do not apply more than 300 V dc or ac rms (sine) between terminals or between any terminal and earth ground. Before each use, verify the meter's operation by measuring a known voltage. When servicing the meter, use only specified replacement parts. Use caution when working above 30 V ac rms, 42 V ac peak, or 60 V dc. Such voltages pose a shock hazard. Keep your fingers behind the finger guards on the probe when making measurements. Connect the common test lead before connecting the live test lead. Disconnect the live test lead first. Remove test leads from the meter before opening the case. Use only a single 9 V battery, properly installed in the meter case, to power the meter. Follow all equipment safety procedures. Before measuring current, check the meter's fuses (see "How to Test the Fuse"). Never touch the probe to a voltage source when the test leads are plugged into the 10 A input jack.

ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ

ˇ ˇ ˇ ˇ

Always use clamp-on probes (dc current clamps) when measuring current exceeding 10 A. DO NOT connect thermocouple to voltages exceeding 30 V. Always use a high voltage probe to measure voltage if peak voltage might exceed 300 V. To avoid false readings, which could lead to possible electric shock or personal injury, replace the meter's battery as soon as the low battery indicator (N) appears. To avoid fire hazard, only use a fuse identical in type, voltage rating, and current rating to that specified on the fuse rating label located on the case bottom. Do not operate the meter if it is disassembled. Always operate the meter with the case top and bottom properly assembled. Disassembly procedures and warnings are in the 78 Automotive Service Manual. Service procedures are for qualified personnel only. Caution To avoid possible damage to the meter or to equipment under test:

ˇ

ˇ

ˇ

Disconnect the power to the circuit under test and discharge all high voltage capacitors before testing resistance, continuity or diodes. Use the proper function and range for your measurement applications. When measuring current, turn off circuit power before connecting the meter in the circuit. Remember to place the meter in series with the current.
Symbols Symbol Meaning Important information. See manual. Ground Fuse Double insulation (Protection Class II) Conforms to European Union directives

ˇ ˇ

Table of Contents

Chapter 1

Title

Page

Introduction and Specifications.......................................................... 1-1 1-1. 1-2. 1-3. 1-4. Introduction ........................................................................................... Organization of the Service Manual ..................................................... Conventions ........................................................................................... Specifications ........................................................................................ 1-3 1-3 1-4 1-4

2

Theory of Operation............................................................................. 2-1 2-1. 2-2. 2-3. 2-4. 2-5. 2-6. 2-7. 2-8. 2-9. 2-10. 2-11. 2-12. 2-13. 2-14. 2-15. 2-16. 2-17. 2-18. 2-19. 2-20. 2-21. 2-22. 2-23. 2-24. 2-25. Introduction ........................................................................................... Functional Block Description ............................................................... Circuit Descriptions .............................................................................. Input Overload Protection ................................................................. Rotary Knob Switch ......................................................................... Input Signal Conditioning Circuits .................................................. Volts Functions ............................................................................ Ohms Function ............................................................................ Continuity .................................................................................... Temperature Function .................................................................. Diode Test Function .................................................................... RPM Function .............................................................................. Current Function .......................................................................... Analog Section of Integrated Multimeter IC (U1) .......................... Frequency Measurements ............................................................ Dwell and Duty Cycle Measurements ......................................... Microcomputer Control .................................................................... Peripherals to U1 ............................................................................... AC Buffer ..................................................................................... AC converter ................................................................................. Active Filter .................................................................................. A/D Converter .............................................................................. Beeper ........................................................................................... Power Supply ................................................................................ Display .............................................................................................. 2-3 2-3 2-4 2-4 2-4 2-4 2-4 2-5 2-6 2-6 2-7 2-7 2-7 2-7 2-9 2-9 2-9 2-9 2-9 2-9 2-9 2-9 2-10 2-10 2-10

3

Maintenance ......................................................................................... 3-1
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3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 3-7. 3-8. 3-9. 3-10. 3-11. 3-12. 3-13. 3-14. 3-15. 3-16. 3-17. 3-18. 3-19. 3-20. 3-21. 3-22. 3-23. 3-24. 3-25. 3-26. 3-27. 3-28. 3-29. 3-30. 4

Introduction ........................................................................................... Recommended Equipment .................................................................... Operator Maintenance ........................................................................... Case Disassembly ............................................................................. Battery Replacement ......................................................................... Fuse Test ........................................................................................... Fuse Replacement ............................................................................. Circuit Assembly Removal ............................................................... Display Access .................................................................................. Cleaning ................................................................................................. Performance Tests ................................................................................. Setup .................................................................................................. Display Test ...................................................................................... DC Voltage Test ................................................................................ AC Voltage Test ................................................................................ Frequency Test .................................................................................. Frequency, Dwell, and Duty Cycle Trigger Level Test .................... RPM Test .......................................................................................... Ohms Test ......................................................................................... Continuity Test .................................................................................. Diode Test ......................................................................................... DC and AC Current Test ................................................................... Temperature Test .............................................................................. RPM80 Inductive Pickup Test (Optional Accessory) ....................... Calibration ............................................................................................. Troubleshooting .................................................................................... Surface Mount Assemblies ............................................................... Power Supply Related Troubleshooting ........................................... Common (Shunt) Regulator Troubleshooting .................................. Vdd (Series) Regulator Troubleshooting ..........................................

3-3 3-3 3-3 3-3 3-3 3-5 3-5 3-5 3-5 3-7 3-7 3-7 3-8 3-8 3-9 3-9 3-10 3-10 3-11 3-11 3-12 3-12 3-12 3-14 3-17 3-18 3-18 3-18 3-19 3-20

List of Replaceable Parts .................................................................... 4-1 4-1. 4-2. 4-3. 4-4. 4-5. Introduction ........................................................................................... How to Obtain Parts .............................................................................. Manual Status Information .................................................................... Service Centers ...................................................................................... Parts Lists .............................................................................................. 4-3 4-3 4-3 4-4 4-4

5

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

ii

List of Tables

Table 1-1. 2-1. 3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 3-7. 3-8. 3-9. 3-10. 3-11. 3-12. 4-1. 4-2. 5-1.

Title Specifications........................................................................................................... Typical Voltage Levels and Tolerance (Referenced to Common) .......................... Recommended Test Equipment............................................................................... DC Voltage Test ...................................................................................................... AC Voltage Test ...................................................................................................... Frequency Test......................................................................................................... Frequency, Dwell, and Duty Cycle Trigger Level Test .......................................... RPM Test ................................................................................................................. Resistance Test ........................................................................................................ Continuity Test ........................................................................................................ Diode Test................................................................................................................ DC and AC Current Test ......................................................................................... Functional Description of Power Supply Components ........................................... Voltage Levels ......................................................................................................... Fluke 78 Final Assembly ......................................................................................... A1 Main PCA .......................................................................................................... Signal Abbreviations ...............................................................................................

Page 1-5 2-10 3-4 3-8 3-9 3-9 3-10 3-10 3-11 3-11 3-12 3-12 3-19 3-19 4-5 4-7 5-3

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iv

List of Figures

Figure 2-1. 2-2. 2-3. 2-4. 3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 4-1. 5-1.

Title Block Diagram......................................................................................................... 4 V Range Simplified Schematic............................................................................. 400 Ohm Range Simplified Schematic ................................................................... A/D Converter ......................................................................................................... Disassembled Fluke 78 ............................................................................................ Display..................................................................................................................... Ambient Temperature Lag Bath .............................................................................. Setup for RPM80 Inductive Pickup Test ................................................................. Typical Waveforms for Inductive Pickup Test ....................................................... Calibration Adjustment Point .................................................................................. Fluke Final Assembly ............................................................................................. A1 Main PCA ..........................................................................................................

Page 2-3 2-5 2-6 2-8 3-6 3-8 3-13 3-15 3-16 3-17 4-6 5-5

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Chapter 1

Introduction and Specifications

Title 1-1. 1-2. 1-3. 1-4. Introduction ............................................................................................ Organization of the Service Manual ...................................................... Conventions............................................................................................ Specifications .........................................................................................

Page 1-3 1-3 1-4 1-4

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1-2

Introduction and Specifications Introduction

1

1-1. Introduction
This Service Manual provides information on maintaining, troubleshooting, and repairing the Fluke 78 Automotive Meter. This information includes the following: ˇ ˇ ˇ ˇ ˇ ˇ Specifications Theory of operation Calibration Performance testing and troubleshooting procedures Replacement parts lists 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. If the warranty has expired, the meter will be repaired and returned for a fixed fee. Contact the nearest Service Center for information and prices. A list of U.S. and International Fluke telephone numbers is included at the end of Chapter 4 of this manual.

1-2. Organization of the Service Manual
This service manual has the following five chapters.

Chapter 1. Introduction and Specifications Chapter 1 describes the Service Manual, explains special terminology and conventions, and provides complete meter specifications. Chapter 2. Theory of Operation Chapter 2 treats the meter's circuitry as 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 explain operation to the component level and support the troubleshooting and repair procedures in Chapter 3. Chapter 3. Maintenance Chapter 3 provides maintenance information, detailed repair procedures to the component level, and performance tests. Troubleshooting and repair procedures rely on the Theory of Operation presented in Chapter 2 and the Schematic Diagrams in Chapter 5. Chapter 4. List of Replaceable Parts Chapter 4 provides parts lists and information on how and where to order parts. Chapter 5. Schematic Diagrams Chapter 5 provides schematic diagrams for all assemblies and a list of mnemonic definitions to aid in identifying signal name abbreviations.

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1-3. Conventions
The following conventions are used in this manual: ˇ ˇ Printed Circuit Assembly (PCA) A "pca" is a printed circuit board and its attached parts. Circuit Nodes A pin or connection on a component is specified by a dash (-) and number following the component reference designator. For example, pin 19 of U30 would be U30-19. ˇ User Notation Switch positions, input terminals, and display annunciators are usually shown as they appear on the meter. Mnemonics used in the meter circuit descriptions correspond to those on the schematic diagrams in Chapter 5.

1-4. Specifications
Specifications for the Fluke 78 are in Table 1-1. Accuracy is specified for a period of one year after calibration, at 18°C to 28°C (64°F to 82°F) with relative humidity to 95%. AC conversions are ac-coupled, average responding, and calibrated to the rms value of a sine wave input. Accuracy Specifications are given as: ą([% of reading] + number of least significant digits)

1-4

Introduction and Specifications Specifications

1

Table 1-1. Specifications Maximum Voltage Between any Terminal and Earth Ground Fuse Protection Display

300 V 15 A 600 V FAST Fuse Digital: 4000 counts, updates 4/s Bar Graph: 64 segments, update rate 40/s Frequency: 9,999 counts, updates 3/s

Operating Temperature Storage Temperature Temperature Coefficient Relative Humidity

0°C to 55°C (32°F to 131°F) 40°C to 60°C (40°F to 140°F) 0.1 x (specified accuracy) per °C ambient (<18°C or >28°C). Temperature, 0.04% + 0.1°C per °C 0% to 95%, to 30°C (86°F) 0% to 75%, to 40°C (104°F) 0% to 45%, to 55°C (131°F)

Altitude Electromagnetic Compatibility

2000 meters maximum In an RF field of 1 V/m on all ranges and functions: Total Accuracy = Specified Accuracy +0.7% or range Performance above 1 V/m is not specified. 9 V, NEDA 1604 or 6F22 or 006P Alkaline: 500 hrs (typical) Carbonzinc: 300 hrs (typical) 4096 Hz Per MILT28800E for a Type III, Class 3 Style D, Instrument 1.12 in x 2.95 in x 6.55 in (2.8 cm x 7.5 cm x 16.6 cm) 12 oz (340g) Complies with EN 610101:1993, ANSI/ISA S82.011994 and CAN/CSA C22.2 No. 1010.192 Overvoltage Category II. CSA Certified, TUV Product Service licensed, UL Complies with FCC Part 15, Class B, VDE 0871B, Vfg. 2431991 Input: Magnetic field from spark plug Output: Pulse to trigger Fluke 78 Type: K (Chromel vs. Alumel) (Fluke 80PK1) Not suitable for immersion in liquid. Accuracy: ą1.1°C (2°F) between 0°C to 260°C (32°F-500°F). Typically within 1.1°C (2°F) of NBS tables for temperatures between 40°C (40°F) to 0°C (32°F). Temperature Range: 40°C to 260°C. (40°F to 500°F). Above 260°C (500°F), toxic gas might be emitted. NOTE: The temperature range is primarily a function of the thermal limitations of the thermocouple's insulation. Cable Insulation: Teflon

Battery Type Battery Life Continuity Beeper Shock, Vibration Size (HxWxL) Weight Safety Safety Approvals EMI Regulation Inductive Pickup Thermocouple

MIN MAX Recording

Accuracy: Specified accuracy of measurement function ą16 digits for changes > 200 ms in duration (ą52 digits in 400 J). Nominal response time (5 to 100% of range) 100 ms to 80%

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Table 1-1. Specifications (cont) Function
AC Volts* (45 Hz to 1 kHz)

Range
4.000 V 40.00 V 300.0 V 300 V -400.0 mV 4000 mV 4.000 V 40.00 V 300.0 V 300 V 400.0 4.000 k 40.00 k 400.0 k 4.000 M 40.00 M 400.0

Resolution
0.001 V 0.01 V 0.1 V 1V -0.1 mV 1 mV 0.001 V 0.01 V 0.1 V 1V 0.1 0.001 00.01 k 000.1 k 0.001 M 0.01 M 0.1

Accuracy

Burden Voltage (Typical)

To 20 kHz DC Volts*

Resistance

Continuity

J J J J J J J

J

J

J J J J J

Diode Test AC Current (45 Hz to 1 kHz) DC Current

2.500 V 10.00 A**

0.001 V 0.01 A

ą (2.5%+2) ą (2.5%+2) N/A ą (2.5%+2) ą (2.5%+2) ą 1.5 dB typical ą (0.3%+5) ą (0.3%+1) ą (0.3%+1) ą (0.3%+1) N/A ą (0.3%+1) ą (0.3%+1) ą (0.5%+2) N/A ą (0.5%+1) ą (0.5%+1) ą (0.5%+1) ą (0.5%+1) ą (1%+3) Beeper on @ Open circuit voltage <30 for < 1.5 V short of 1 ms or longer ą 2% typical Open circuit voltage < 3.3 V

J

ą (2.5%+2) ą (1.0%+5) ą (1.0%+2)

0.03 V/A 0.03 V/A 0.03 V/A

4.000 A 0.001 A 10.00 A** 0.01 A * Input impedance: 10 M (nominal), < 150 pF. ** 10 A continuous, 20 A overload for 30 seconds maximum.

J

Function
Frequency (1 Hz to 20 kHz)

Range
99.99 999.9 9.999 kHz 20.00 kHz >20.00 kHz to 99.99 kHz 500.0 kHz 70-7,000 RPM (usable to 9,999) 120-7,000 RPM (usable to 9,999) 0-120 0.0-99.9% (1 Hz to 20 kHz, pulse width> 5 ľs) -40 to +999°C @ >20°C ambient, to +980°C below 20°C ambient

Resolution
0.01 Hz 0.1 Hz 0.001 kHz 0.01 kHz 0.01 kHz 0.1 kHz 1RPM 1RPM 1 degree 0.1%

Accuracy

ą 0.01%+2) ą (0.01%+2) ą (0.01%+2) ą (0.01%+2) (107 V-Hz maximum) Usable Usable RPM 1 ą (0.2% + 2) RPM 1 ą (0.2% + 2) Dwell Angle ą 2 degrees Duty Cycle ą (0.2% per kHz +0.1%) (for rise time <1 ľs) Temperature* 1 degree ą (0.3%+6°C) @ -40 to -20°C ą (0.3%+4°C) @ -20 to 0°C ą (0.3%+3°C) @ 0 to 170°C ą (0.3%+5°C) @ 170 to 260°C ą (0.3%+6°C) @ 260 to 700°C ą (0.3%+7°C) @ 700 to 999°C * When measuring temperature, the accuracy of the system is the combined accuracy of the meter and the thermocouple.

1-6

Introduction and Specifications Specifications
Table 1-1 Specifications (cont) Frequency Counter Sensitivity and Trigger Level Minimum Sensitivity Approximate Trigger Level (Rms Sine Wave) (DC Volts Function) 1 Hz to 5 Hz 5 Hz to 20 kHz --400 mV --400 mV 0.7 V 0.3 V 1.7 V 7V 3V 4V 70 V 30 V 40 V

1

Input Range

400.0 mV dc 4000 mV dc 4.00 V 40.00 V 300.0

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1-8

Chapter 2

Theory of Operation

Title 2-1. 2-2. 2-3. 2-4. 2-5. 2-6. 2-7. 2-8. 2-9. 2-10. 2-11. 2-12. 2-13. 2-14. 2-15. 2-16. 2-17. 2-18. 2-19. 2-20. 2-21. 2-22. 2-23. 2-24. 2-25. Introduction ............................................................................................ Functional Block Description................................................................. Circuit Descriptions................................................................................ Input Overload Protection.................................................................. Rotary Knob Switch........................................................................... Input Signal Conditioning Circuits .................................................... Volts Functions.............................................................................. Ohms Function .............................................................................. Continuity ...................................................................................... Temperature Function.................................................................... Diode Test Function ...................................................................... RPM Function................................................................................ Current Function............................................................................ Analog Section of Integrated Multimeter IC (U1) ............................ Frequency Measurements .............................................................. Dwell and Duty Cycle Measurements ........................................... Microcomputer Control ..................................................................... Peripherals to U1................................................................................ AC Buffer ...................................................................................... AC converter.................................................................................. Active Filter................................................................................... A/D Converter ............................................................................... Beeper ............................................................................................ Power Supply................................................................................. Display ...............................................................................................

Page 2-3 2-3 2-4 2-4 2-4 2-4 2-4 2-5 2-6 2-6 2-7 2-7 2-7 2-7 2-9 2-9 2-9 2-9 2-9 2-9 2-9 2-9 2-10 2-10 2-10

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Theory of Operation Introduction

2

2-1. Introduction
Chapter 2 provides theory of operation for the Fluke 78 Automotive Meter. An overview of circuit operation is presented in the form of functional block descriptions. Circuit descriptions cover the major circuit functions in more detail. Schematic diagrams are in Chapter 5.

2-2. Functional Block Description
The instrument is partitioned into analog and digital sections. See Figure 2-1. The integrated multimeter IC (U1) performs both analog and digital functions, which are explained in more detail below. The analog section of U1 contains the a/d converter, active filter, ac converter, frequency comparator, analog signal routing, range switching, and power supply functions. The digital section of U1 executes software functions, formats data for the display, drives the display, and controls most analog and digital logic functions. The pushbutton selects various operating modes for the meter. Output from the digital section can be viewed on the liquid crystal display (LCD) and is audible through the beeper.

INPUTS

INPUT PROTECTION

INPUT SIGNAL CONDITIONING U1 INTEGRATED MULTIMETER IC VREF ANALOG SECTION POWER SUPPLY

BEEPER

MICROPROCESSOR

FUNCTION SWITCH

LCD

zr01f.eps

Figure 2-1. Block Diagram

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2-3. Circuit Descriptions
Each of the functional blocks in Figure 2-1 is discussed in more detail in the following paragraphs. Refer to the schematic diagrams in Chapter 5 for circuit details not provided in this chapter.

2-4.

Input Overload Protection The zinput is protected from overload by a network consisting of metal-oxide varistor (RV1), three current-limiting resistors (R1, R2, and RT1) and spark gap E1. Under extremely high energy conditions, R1 will help limit overload current until RT1 heats up. Thermistor RT1 rises to a high impedance during a sustained voltage overload in the ohms or temperature mode. Transistors Q1 and Q2 form a voltage clamp network. This clamp performs a current-limiting function on the overload current to U1 at 10 mA during ohms and temperature overloads. Power supply regulation and system operation is maintained during any of these overloads. The 10 A input is protected from overloads by F1 (15 A/600 V). R40 limits the input current in RPM, while Q11 and Q12 clamp the voltage seen by U4. Rotary Knob Switch Input signals are routed from the overload protection circuits to a double-sided switch wafer. This switch wafer provides the necessary connections to implement signal conditioning and function-encoding for U1. Input Signal Conditioning Circuits Each input signal is routed through signal conditioning circuitry before reaching IC U1. Incoming signals received through thez input are routed to precision resistor network Z1. This divider network precisely scales the input for the various voltage ranges and provides precision reference resistors that are used for the ohms and capacitance functions.
Input divider Z1 is used in two modes, series and parallel. In volts functions, a series mode provides four divider ratios. In the ohms function, a parallel mode provides five reference resistors.

2-5.

2-6.

2-7.

Volts Functions During the following discussion of the volts function, refer to schematic and signal flow diagrams in Chapter 5. In volts functions, signal flow for input divider Z1 begins with a voltage that appears at the z input. (See Figure 2-2, 4V Range Simplified Schematic.) This input is connected to the high end of the 9.996-MJ resistor (Z1-1) through R1 and RT1. If the AC volts function is selected, dc blocking capacitor C1 is also connected in series. If the DC volts function is selected, C1 is shorted by S1 (contacts 5 and 6).
Internal switches connect the 9.996-MJ and 1.1111-MJ resistors (Z1-2 and -3). The low end of the 1.1111-MJ resistor (Z1-7) is connected to the COM input through S1 contacts 11 and 12. This produces the divide-by-10 ratio needed for the 400 mV dc, 4000 mV dc, 4 V dc, and 4 V ac ranges. The 4 V ac range requires frequency compensation, which is supplied by C2. For the 40 V range, internal switches connect the Z1-4 (101.01 kJ) resistor to provide a divide-by-100 ratio. In the 300.0 V range, Z1-5 (10.01 kJ) produces a divide-by-1,000 ratio. And in the 300 V range, the Z1-6 (1.0001kJ) resistor provides a divide-by-10,000 ratio.

2-4

Theory of Operation Circuit Descriptions

2

C1 R1+RT1 6 S1 5 1 C2 2 4 VAC 4V

V/

Z1 9.996M

DC ACTIVE FILTER HIGH 3 7 A/D AC AC CONVERTER

Z1 1.1111M

12 S1 11 COM

LOW

zr02f.eps

Figure 2-2. 4 V Range Simplified Schematic

2-8.

Ohms Function When the 400-ohm range is selected, internal switches connect the resistor Z1-2 (9.996 MJ) to resistor Z1-6 (1.0001 kJ). (See Figure 2-3, 400-Ohm Range Simplified Schematic.) Then through switch contacts S1 5, 6, and 9, these resistors form a reference resistor of 1 kJ.
The source voltage is connected internally at both V0 and V4 of U1. The current is routed through two parallel resistors Z1-6 and Z1-2 (1.0001 kJ and 9.996 MJ) into S1 at contacts 5 and 9. The signal then travels out of S1 at contact 6, through RT1 and R1 and to the z input. The signal then goes through the unknown resistance and back to the COM input. The same current flows through the unknown resistance and the reference resistor. The voltage dropped across the unknown resistance is sensed from the z input jack through R2 and S1 (contacts 2 and 3) to SENS of U1. The a/d converter senses the voltage drop across the 1 kJ reference resistor through the low (RRS of U1 through R8) and high (V0 and V4) points. These two voltages are used by the a/d converter to perform a ratiometric measurement. Since the same current flows through the reference and unknown resistors, the ratio of the resistance values is the same as the ratio of the voltage drops across them. For the 4-kJ range, the 10.010-kJ resistor (Z1-5) used in parallel with the 9.996-MJ resistor (Z1-2) forms a 10-kJ reference resistor. For the 40-kJ range, 101.01 kJ(Z1-4) and 9.996 MJform a 100-kJ reference resistor. And for the 400-kJ range, 1.1111 MJ (Z1-3) and 9.996 MJ provide a 1-MJ reference resistor. The 4-MJ and 40-MJ ranges use the 9.996-MJ resistor alone.

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2-9.

Continuity The continuity function is the 400 J range of the ohms function with no active filtering of the input signal. A comparator is used to turn on the beeper when the input drops below about 50 J.

2-10. Temperature Function The thermocouple voltage is measured by the a/d converter through R2, S1-2 and S1-3, and the SENS input of U1-93. The voltage is the result of any temperature difference between the thermocouple and the reference junction (at the meter). U3 produces an output voltage of 10 mV per degree C, proportional to the meter temperature (reference junction), which is divided by R15 and R16, and measured by the a/d converter. The thermocouple and reference junction measurements are combined, resulting in the temperature of the thermocouple.
At the beginning of each measurement cycle, an open thermocouple detect voltage (OTD, U1-89) is applied to the U1 SENS input through resistor R12. If the thermocouple wire is broken (open) or not installed, the SENS is driven high enough to be measured as an overload. The display then flashes the meter (reference junction) temperature.

OHMS VOLTAGE SOURCE IX LOW

REFERENCE RESISTOR Z1 9.996M 1 2 Z1 1.0001k 7 6 + VRREF R8

A/D INTEGRATE REFERENCE

HIGH 5 S1 6 9 S1 6

R1+RT1 R2

ACTIVE FILTER

HIGH A/D INTEGRATE UNKNOWN R LOW

RX UNKNOWN RESISTOR

+ VRX

RX IXˇRX VR X = = IXˇRREF R REF VR REF
zr03f.eps

Figure 2-3. 400 Ohm Range Simplified Schematic

2-6

Theory of Operation Circuit Descriptions

2

2-11. Diode Test Function Q4 provides the source current for the diode test function. The input is sensed through R2. R2 and R9 form a 10:1 divider for measuring the voltage in diode test. A single beep sounds when the input drops below about 0.77 V; a continuous tone sounds for inputs below about 60 mV. 2-12. RPM Function The output signal pulses of the RPM80 Inductive Pickup are divided by input resistors R40 and R41, then applied to comparator U4. Resistors R42 and R43 set the trigger level for U4 (and the protection clamp voltage for Q12), while R44 and R45 provide hysteresis. When Q13 is turned on, R47 parallels R43, resulting in the lower input trigger level. Q13 off produces the higher input trigger level. The lower trigger level is annunciated on the display as a 4 V range, while the higher trigger level is annunciated as a 40 V range. The output of U4 drives the frequency counter in U1. To convert to rpm, the frequency is multiplied by 60 for RPM1 (1 revolution/spark), or 120 for RPM2 (2 revolutions/spark). The 10 A input serves as a common for the RPM input. Fuse F1 must be intact for RPM to work. 2-13. Current Function Input current through R11 develops a voltage that is proportional to the input. The dc voltage is routed to the active filter and a/d converter inside U1. The ac voltage is routed to the ac buffer, ac converter, active filter, and a/d converter. 2-14. Analog Section of Integrated Multimeter IC (U1) The a/d converter, autorange switching, frequency comparator, and most of the remaining analog circuitry are contained in the analog section of U1. Peripherals to this U1 analog section include the crystal clock, the system reference voltage, the filter and amplifier resistors, and capacitors.
U1 uses the dual-rate, dual-slope a/d converter circuit shown in Figure 2-4, A/D Converter. For most measurements, the basic a/d conversion cycle is 25 ms, for a rate of 40 measurements per second. A single conversion at this rate is called a minor cycle sample. Each minor cycle sample is used to provide updates at a rate of 40 per second for the fast response bar graph display, and also provides fast autoranging. Eight minor cycle samples are necessary to accumulate data for displaying a fullresolution (4000-count full scale) measurement on the digital display. A 40-ms autozero phase occurs following every eight-sample sequence. Therefore, each digital display update requires 240 ms, approximating four updates per second. Basic a/d conversion elements and waveforms are illustrated in Figure 2-4, A/D Converter. A voltage level proportional to the unknown input signal charges (integrates) integrator capacitor C12 for an exact amount of time. This capacitor is then discharged by a reference voltage of opposite polarity. The discharge (read) time, which is proportional to the level of the unknown input signal, is measured by the digital circuits in U1 and sent to the display. Basic timing for the a/d converter is defined as a series of eight integrate and read cycles, followed by a 40-ms autozero phase. However, the 40-MJ, overload recovery, and autoranging modes all require variations from the basic timing.

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BUFFER

INTEGRATOR

COMPARATOR REFER TO WAVEFORM

INPUT VOLTAGE

1

+ +

+

COMPARE 2

3 A/D CONTROL 4 + VOLTAGE REFERENCE 131.072 kHz CLOCK

5

SWITCH NO. 1 2 3 4 5

AUTO ZERO

INTEREAD READ GRATE +INPUT INPUT ON

HOLD

MICROCOMPUTER

ON

ON ON ON

ON

ON

ON

ON

INTEGRATE ZERO RAMP BASELINE

READ RAMP

HOLD

AUTO ZERO

16.7 ms SAMPLE #1

8.33 ms SAMPLE #2 SAMPLE #8

REPEAT

8 MINOR CONVERSIONS, 200 ms (1 FULL RESOLUTION CONVERSION) AS SEEN AT INTEGRATOR OUTPUT

CONTROL

zr04f.eps

Figure 2-4. A/D Converter

2-8

Theory of Operation Circuit Descriptions

2

2-15. Frequency Measurements A voltage comparator is used for both signal detection in frequency mode and threshold detection in continuity mode. In frequency mode, digital pulses from the voltage comparator are routed to the counter. Pressing the range push button while in frequency mode causes a range change in the primary function (ac or dc volts) that may change the sensitivity. 2-16. Dwell and Duty Cycle Measurements Dwell is a duty cycle measurement of the input waveform taken in the 40 V dc range. A voltage comparator and frequency counter are used. Information from the selected number of cylinders is combined with the duty cycle to compute dwell (the number of degrees of distributor rotation that the points are closed).
The duty cycle function is performed in the 4 V dc range. Changing the trigger slope in Duty Cycle (momentary button press) also changes the trigger slope for Dwell. The meter returns to the default slope (-) when entering the sleep mode or when turned off.

2-17. Microcomputer Control A microcomputer, integrated within U1, controls the various instrument functions and drives the display. The position of the rotary switch, S1, is decoded by the microcomputer from the three inputs F0, F1, and F2. All function modes, input ranging, signal routing, active filter enable, a/d timing, and mode are controlled by the microcomputer. 2-18. Peripherals to U1 In addition to input overload protection and input signal conditioning circuits, other devices peripheral to U1 are needed to support the meter's features. The ac converter, active filter, and a/d converter circuits require off-chip resistors and capacitors. Digital drive and level-shifting circuits are needed for the beeper drive. A voltage reference is generated separately from U1, and some discrete resistors and transistors support the power supply. 2-19. AC Buffer The ac buffer drives the converter and the frequency comparator and provides a driven guard voltage. 2-20. AC converter The averaging ac converter uses components R14, R18, R19, C4, C6, and C7. This ac converter is a full-wave rectifying converter with a differential output, and it is gain selected to give a dc output equal to the rms value for a sine wave input. Filtering is provided by C4 and C7. 2-21. Active Filter
The active filter uses components R21, R22, C9, and C10. The active filter is a second order low-pass filter with two poles at 5.9 Hz in normal mode. It filters input signal noise and ac ripple from the ac converter, yielding stable a/d converter readings. The microcomputer can disable the filter completely or enable the filter fast response mode by shorting R21 and R22 with internal IC switches.

2-22. A/D Converter
Precision resistor network Z1-8, 9, and 10 connects to the three a/d buffer/integrator range resistors. Z1-8 connects to 190 kJ for the 1-volt (read) range. Z1-9 connects to
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166 kJ for the 400-mV range, and Z1-10 connects to 16 kJ for the 40-mV range. Z1-11 is the summing node of the integrator circuit. The autozero capacitor (C11) stores op amp and comparator offsets. The integrator capacitor is C12. The system reference voltage (1.23 V) is generated by VR1 and R23. The 1.000 V reference voltage for the a/d converter is supplied through U1-1 (REFI). This voltage is adjusted by R26, the dc calibration potentiometer in conjunction with R24 and R25. In addition to generating the a/d reference, the VR1 voltage is used for power supply reference, voltage comparator offset generation, the ohms source voltage, and the open thermocouple detect source voltage.

2-23. Beeper
Devices Q5, Q6, R27, R28, and R29 make up the beeper drive circuit.

2-24. Power Supply
The power supply consists of two regulators, one shunt and one series, which set Vdd at +3.1 V and Vss at -3.2 V for all battery voltages down to about 7 V. The shunt (common) regulator sets |Vdgnd - Vss| (Vdgnd = COM = 0V) and consists of an op amp and current shunt devices integrated on U1. Resistors R34 and R35 provide voltage division. The series (Vdd) regulator, which sets |Vdd-Vdgnd|, is made up of another onchip op amp, along with devices Q7, R32, and R33. Q7 is the series regulator element, and R32 and R33 are for voltage sensing. Capacitors C16 and C17 provide circuit compensation and power supply decoupling for the shunt and series regulators, respectively. Q8 provides base drive for Q7 at turn on. Voltage level information is presented in Table 2-1.

2-25. Display
The liquid-crystal display (LCD) operates under control of the microcomputer. Segments are driven by the computer and displayed on the LCD. Both digital readings and an analog bar-graph display are presented in conjunction with annunciators and decimal points. Refer to the Fluke 78 Users Manual for information about the display.
Table 2-1. Typical Voltage Levels and Tolerance (Referenced to Common) VBT + VDD VSS VBTREFH PS0 PS1 VOA VOB 3.7 ą0.2 3.1 ą0.2 -3.2 ą0.2 -5.3 (battery at full 9 V charge of 6.9 V) -3.2 (battery at low charge of 6.9 V) 1.23 ą0.04 1.23 ą0.15 0 ą0.15 2.2 to 1.7 (referenced from VSS) 1.07 to .85 (referenced from VSS)

2-10

Chapter 3

Maintenance

Title 3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 3-7. 3-8. 3-9. 3-10. 3-11. 3-12. 3-13. 3-14. 3-15. 3-16. 3-17. 3-18. 3-19. 3-20. 3-21. 3-22. 3-23. 3-24. 3-25. 3-26. 3-27. 3-28. 3-29. 3-30. Introduction ............................................................................................ Recommended Equipment ..................................................................... Operator Maintenance ............................................................................ Case Disassembly .............................................................................. Battery Replacement.......................................................................... Fuse Test ............................................................................................ Fuse Replacement .............................................................................. Circuit Assembly Removal ................................................................ Display Access................................................................................... Cleaning.................................................................................................. Performance Tests .................................................................................. Setup................................................................................................... Display Test ....................................................................................... DC Voltage Test................................................................................. AC Voltage Test................................................................................. Frequency Test................................................................................... Frequency, Dwell, and Duty Cycle Trigger Level Test..................... RPM Test ........................................................................................... Ohms Test .......................................................................................... Continuity Test................................................................................... Diode Test .......................................................................................... DC and AC Current Test.................................................................... Temperature Test ............................................................................... RPM80 Inductive Pickup Test (Optional Accessory)........................ Calibration.............................................................................................. Troubleshooting ..................................................................................... Surface Mount Assemblies ................................................................ Power Supply Related Troubleshooting ............................................ Common (Shunt) Regulator Troubleshooting ................................... Vdd (Series) Regulator Troubleshooting...........................................

Page 3-3 3-3 3-3 3-3 3-3 3-5 3-5 3-5 3-5 3-7 3-7 3-7 3-8 3-8 3-9 3-9 3-10 3-10 3-11 3-11 3-12 3-12 3-12 3-14 3-17 3-18 3-18 3-18 3-19 3-20

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Maintenance Introduction

3

WWarning
Service procedures described in Chapter 3 should be performed by qualified personnel only. To avoid electric shock, perform only those procedures described in this service manual.

3-1. Introduction
Chapter 3 contains maintenance information for the Fluke 78 meter and includes performance tests, calibration, general maintenance procedures, and troubleshooting. For operator maintenance, refer to the Fluke 78 Users Manual. The performance tests are recommended as a preventive maintenance tool to verify proper instrument operation. A one year calibration cycle is recommended to maintain the specifications given in the Users Manual.

3-2. Recommended Equipment
Test equipment recommended for the performance tests and calibration is listed in Table 3-1. If the recommended equipment is not available, instruments with equivalent specifications may be used.

3-3. Operator Maintenance
WWarning
To avoid electrical shock, remove the test leads before opening the case, and close the case before operating the meter. To prevent fire, install fuse with the rating shown on the back of the meter. Caution To avoid contamination with oil from the fingers, handle the pca by the edges or wear gloves. PCA contamination may not cause immediate instrument failure in controlled environments. Failures typically show up when contaminated units are operated in humid areas.

3-4.

Case Disassembly
Use the following procedure to disassemble the case: 1. Set the rotary switch to OFF and disconnect the test leads if they are installed. 2. Remove the four Phillips screws from the case bottom. 3. Turn the meter face up, grasp the case top, and pull the case top from the meter.

3-5.

Battery Replacement

WWarning
To avoid false readings, which could lead to possible electric shock or personal injury, replace the battery as soon as the battery indicator (N) appears. The meter is powered by a single 9 V battery (NEDA 1604, 6F22, or 006P). Refer to Figure 3-1, and use the following procedure to replace the battery: 1. Remove the upper case as described under Case Disassembly. 2. Lift the battery from the case bottom and install the new battery.
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Table 3-1. Recommended Test Equipment Equipment DMM Calibrator Minimum Specifications DC Voltage: 0-500 V Accuracy: .05% AC Voltage: 0-500 V Accuracy: 0.5% Frequency: 100 Hz-20 kHz DCA: 3.5-10 A Accuracy: 0.2% ACA: 10 A Accuracy: 0.5% Frequency: 45 Hz-1 kHz Range: 0-35 MJ Accuracy: 0.1% High Accuracy Function Generator Waveforms: Sine, Square & Triangle Voltage: 8 V peak DC offset voltage: 0-4 V Frequency: 10 Hz-20 kHz Frequency Accuracy: .002% DMM 100 mV DC Voltage Range Accuracy: 0.5% Resolution: 100 ľ V Accuracy: 0.2 °C @ Ambient Resolution: 0.1 °C or °F. Must fit inside of a banana jack Lag Bath Room Temperature Water For Testing the RPM-80 Inductive Pickup Function Generator Single Cycle Triangle Waveform, -pi/2 Start Phase, 10 ms Repetition Rate Frequency: 600 Hz Output Voltage: 20 V (unterminated) 50 MHz, 3% vertical error 2 10X scope probes Binding Post to BNC Male 10 Ohm, ą 1.0% 14 or 16 AWG, 1 foot insulated Philips Models PM 5133 or PM 5134 Fluke 20 Series, 70 Series or 80 Series Mercury or Digital Fluke 80T-150U Philips Models PM 5191, PM 5192, or PM 5193 Recommended Model Fluke Model 5500A

Thermometer Temperature Probe

Oscilloscope Adapter Resistor Wire

Philips PM 3055, Fluke 93, 95, or 97 Pomona Model 1296 NA NA

3-4

Maintenance Operator Maintenance

3

3-6.

Fuse Test Use the following procedure to test the meter's internal fuse:
1. Turn the rotary selector switch to the J position. 2. Plug a test lead into the z input terminal, and touch the probe to the 10 A input terminal. 3. The display should indicate between 0.1 and 0.5 ohms. This tests F1 (15 A, 600 V). If the display reads OL (overload), replace the fuse and test again. If the display reads any other value, further servicing is required.

3-7.

Fuse Replacement Refer to Figure 3-1, and use the following procedure to examine or replace the meter's fuses:
1. Remove the upper case. 2. Remove the defective fuse by gently prying one end of the fuse loose and sliding the fuse out of the fuse bracket. 3. Install a new fuse of the same size and rating. Make sure the new fuse is centered in the fuse holder. 4. Ensure that the case top rotary switch and circuit board switch are in the OFF position. 5. Reinstall the four Phillips screws into the case bottom.

3-8.

Circuit Assembly Removal 1. Remove the 15 A fuse (F1) to access the screw that holds the pca to the case bottom (refer to Fuse Replacement, above).
Note Be careful not to lose the spring located directly under the screw on the back side of the pca. 2. Remove the pca from the case bottom.

3-9.

Display Access
Caution To prevent contamination, do not handle the conductive edges of the LCD interconnects. If they are contaminated, clean them with alcohol. Refer to Figure 3-1. 1. Remove the four Phillips screws from the back side of the pca. 2. Remove the LCD assembly. 3. Insert a small screwdriver under the edges of the display mask bracket, and gently pry the bracket loose from the snaps. 4. Turn the bracket (with LCD) upside down to remove the LCD. 5. Before installing a new LCD, make sure that all connector contact points are clean. If needed, they may be cleaned with alcohol.
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DECAL WINDOW KNOB ASSEMBLY

DECAL, TOP CASE

TOP CASE LCD, WINDOW FUSE LCD, ASSEMBLY SHIELD, TOP SCREW 4-24 ROTORY SWITCH SCREW 4-14X3/8 SHIELD, BOTTOM BATTERY, 9V MAIN PRINTED CIRCUIT ASSEMBLY

SCREW #2-14X3/8

CONTACT, ANNUCIATOR TRANSDUCER

SPRING

CASE, BOTTOM

4 X FOOT, NON-SKID 4 X SCREW 5-14X3/4

KNOB ASSEMBLY

SPRING DETENT MASK,BRACKET

LCD

SWITCH, MOMENTARY

BRACKET, LCD SHOCK ABSORBER

SHAFT, KNOB

MASK,BRACKET

LCD ASSEMBLY KNOB ASSEMBLY

zr05f.eps

Figure 3-1. Disassembled Fluke 78

3-6

Maintenance Cleaning

3

3-10. Cleaning
Caution To avoid damaging the meter, do not use aromatic hydrocarbons or chlorinated solvents for cleaning. These solutions will react with the plastics used in the instruments. Do not allow the LCD to get wet. Remove the display assembly before washing the pca and do not reinstall it until the pca is completely dry. Do not use detergent of any kind for cleaning the pca. Do not remove lubricants from the switch when cleaning the pca. 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.

3-11. Performance Tests
Performance tests are recommended for incoming inspection, periodic maintenance, and for verifying the specifications. If the instrument fails any part of the test, calibration and/or repair is indicated.

3-12. Setup 1. Allow the Fluke 78 to stabilize to room temperature 23°C +/- 5°C (73°F +/- 9°F).
2. Check the fuse and battery, and replace them if necessary. (Refer to the battery and fuse replacement procedures in this chapter.)

WWarning
To prevent fire, install the fuse in accordance with the rating shown on the back of the meter. Injury hazard. Connect the ground/common/low side of the ac calibrator to common on the Fluke 78.

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3-13. Display Test To test the display, hold the pushbutton down and turn the Fluke 78 on. All segments will remain on as long as the pushbutton is held down. Check whether all display segments come on as indicated in Figure 3-2.

AC DC mV Mk Hz RPM 1 2
0 MAX 1 MIN 2 3
AUTO

4000 V

zr06f.eps

Figure 3-2. Display

3-14. DC Voltage Test 1. Set the Fluke 78 rotary switch to F and connect the DC Voltage Calibrator output to the z and COM input terminals of the meter.
Note For autorange to include the 400 mV (lowest) range, press the pushbutton three times. 2. Referring to Table 3-2, set the DC Voltage Calibrator for the output indicated, and verify that the Fluke 78 display reading is within the limits shown. 3. Reset the source to 0 V.
Table 3-2. DC Voltage Test Step Range 1 2 3 400.0 mV 4000 mV or 4.000 V 4000 mV or 4.000 V short +3.500 V - 3.500 V Input Voltage 0 to +/-000.5 m V DC 3488 to 3512 V mV DC or 3.488 to 3.512 V DC -3488 to 3512 mV DC -3.488 to -3.512 V DC (and within 2 counts of +3.5 V reading) 34.88 to 35.12 V DC 348.8 to 351.2 V DC 497 to 503 V DC Display Reading

4 5 6

40.00 V 300.00 V 300 V

+35.00 V +350 V +500 V

3-8

Maintenance Performance Tests

3

3-15. AC Voltage Test

WWarning
Injury hazard. Connect the ground/common/low side of the AC calibrator to common on the Fluke 78. 1. Set the Fluke 78 rotary switch to K and connect the AC Voltage Calibrator to the z and COM input terminals. 2. Set the AC Voltage Calibrator for the output given in Table 3-3, and verify that the Fluke 78 display reading is within the limits shown in the table. 3. Reset the source to 0 V. Note When the input is open in the V AC function, it is normal for the meter to read some counts on the display. This is due to the ac pickup in the ac amplifier when the ac amplifier is unterminated.
Table 3-3. AC Voltage Test Step 1 2 3 4 5 6 Range 4V 4V 4V 40 V 300.0 V 300 V Input Voltage short 3.500 V 3.500 V 35.00 V 350 V 500 V Frequency ---100 Hz 1 kHz 1 kHz 1 kHz 1 kHz Display Reading 0 to .002 V AC 3.410 to 3.590 V AC 3.410 to 3.590 V AC 34.10 to 35.90 V AC 341.0 to 359.0 V AC 485 to 515 V AC

3-16. Frequency Test 1. Set the Fluke 78 rotary switch to HzB and press the pushbutton for 2 seconds to put the meter in the ac-coupled frequency function.
2. Connect the Function Generator output to the z and COM input terminals of the meter. Note The frequency accuracy of the Function Generator must be appropriate for the specified accuracy of the Fluke 78. 3. Referring to Table 3-4, set the Function Generator for the output indicated in the steps. Verify that the Fluke 78 display reading is within the limits shown in the table.
Table 3-4. Frequency Test Step Range 1 4V Sine Wave Input Voltage 300 mV rms (848 mV p-p) Frequency 20 kHz 19.98 kHz to 20.02 kHz Display Reading

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3-17. Frequency, Dwell, and Duty Cycle Trigger Level Test 1. Connect the High Accuracy Function Generator output to the z and COM input terminals on the Fluke 78.
2. Referring to Table 3-5, set the High Accuracy Function Generator for the output indicated in the steps. 3. Verify that the Fluke 78 display reading is within the limits shown for each function. Note For tests: waveform = Triangle and Frequency = 100 Hz.
Table 3-5. Frequency, Dwell, and Duty Cycle Trigger Level Test Step Function Amplitude (Peak-Peak) 8.00 V 3.40 V DC Offset Display Reading

1 2

Dwell Duty Cycle

4.00 V 1.70 V

4-33 to 4-71 36% to 64%

3-18. RPM Test 1. Connect the High Accuracy Function Generator output to the RPM+ and 10 A input terminals on the Fluke 78.
Note Be sure that fuse F1 is installed and intact for RPM to work. 2. Referring to Table 3-6, set the High Accuracy Function Generator for the output indicated in the steps. Verify that the Fluke 78 display reading is within the limits shown for each range. Note For tests: Waveform = Square and Frequency = 10 Hz.
Table 3-6. RPM Test Step Range Amplitude (peak-peak) 2V 2V 2V 2V DC Offset Display Reading

1 2 3 4

4V 40 V 40 V 4V

1.7 V 1.7 V 3.8 V 3.8 V

1196 to 1204 RPM (2) 0000 RPM (2) 1196 to 1204 RPM (2) 0000 RPM (2)

3-10

Maintenance Performance Tests

3

3-19. Ohms Test 1. Set the Fluke 78 rotary switch to the e function.
2. Connect the Ohms Calibrator or Decade Resistor to the z and COM input terminals of the meter. 3. Referring to Table 3-7, set the Decade Resistor or Ohms Calibrator to the resistance value indicated in steps 1 through 7. Verify that the display reading is within the limits shown in the table.
Table 3-7. Resistance Test Step 1 Decades of 1: 2 3 4 5 6 7 Decades of 1.9: 2 3 4 5 6 7 Decades of 3.5: 2 3 4 5 6 7 Range 400 J 400 J 4 kJ 40 kJ 400 kJ 4 MJ 40 MJ 400 J 4 kJ 40 kJ 400 kJ 4 MJ 40 MJ 400 J 4 kJ 40 kJ 400 kJ 4 MJ 40 MJ Input Resistance short 100 J 1 kJ 10 kJ 100 kJ 1 MJ 10 MJ 190 J 1.9 kJ 19 kJ 190 kJ 1.9 MJ 19 MJ 350 J 3.5 kJ 35 kJ 350 kJ 3.5 MJ 35 MJ Display Reading 000.0 to 000.2 J 99.3 to 100.7 J (plus 0 reading) .994 to 1.006 kJ 9.94 to 10.06 kJ 99.4 to 100.6 kJ .994 to 1.006 MJ 9.87 to 10.13 MJ 188.8 to 191.2 J(plus 0 reading) 1.889 to 1.911 kJ 18.89 to 19.11 kJ 188.9 to 191.1 kJ 1.889 to 1.911 MJ 18.78 to 19.22 MJ 348.0 to 352.0 J (plus 0 reading) 3.481 to 3.519 kJ 34.81 to 35.19 kJ 348.1 to 351.9 kJ 3.481 to 3.519 MJ 34.62 to 35.38 MJ

3-20. Continuity Test 1. Set the Fluke 78 rotary switch to w and press the pushbutton for 2 seconds to put the meter in the continuity test function.
2. Referring to Table 3-8, apply inputs as indicated. Verify that the Fluke 78 display and beeper indicate as shown in the table.
Table 3-8. Continuity Test Step 1 2 Range 400 J 400 J Input open 30 J Display Reading OL tone

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3-21. Diode Test 1. Set the Fluke 78 rotary switch to G and press the pushbutton for 2 seconds to put the meter in the diode test function.
2. Connect the DC Voltage Calibrator output to the zand COM input terminals of the meter. 3. Referring to Table 3-9, set the DC Voltage Calibrator for the output indicated in the steps. Verify that the Fluke 78 display reading is within the limits shown in the table.
Table 3-9. Diode Test Step 1 2 Range 2.45 V 2.45 V Input open +2.00 V OL 1.920 to 2.080 V DC Display Reading

3-22. DC and AC Current Test
1. Set the Fluke 78 rotary switch to A. 2. Set the output of the Current Calibrator to standby and connect it to the 10 A and Common input terminals of the meter. 3. Set the Current Calibrator to the output shown in Table 3-10, and verify that the Fluke 78 display reading is within the limits shown in the table.
Table 3-10. DC and AC Current Test Step Range 1 2 4 A DC 10 A DC Input A +3.5 A +10 A Frequency --3.460 to 3.540 DC 9.88 to 10.12 DC Display Reading

Note To enter AC Amps, press and hold the button for 2 seconds.
3 10 A AC 10 A 1 kHz 9.73 to 10.27 AC

3-23. Temperature Test
Note The meter and any test leads plugged into the input during the temperature test must be at the same room temperature, 23 °C +/-5°C. Handling, and nearby warm equipment, can alter temperature readings. 1. Set the Fluke 78 rotary switch to °C°F. Apply a short between the z and COM inputs. The display will show a steady reading of the meter's internal temperature. 2. Remove the short from the input. The display will flash the same temperature reading about once every 1.3 seconds. 3. Construct an ambient temperature lag bath as shown in Figure 3-3. Immerse the thermometer into the bath.
3-12

Maintenance Performance Tests

3

4. Insert the 80T-150U into the DMM and select a DC mV range with 100 ľV resolution. Turn on the 80T-150U to °C or °F to match the lag bath thermometer. 5. Immerse the probe of the 80T-150U into the lag bath to the same depth as the thermometer and allow the system to stabilize. 6. Note the difference in temperature readings between the 80T-150U/DMM and the lag bath thermometer. If the 80T-150U/DMM reads higher than the thermometer, subtract the difference from the 80T-150U/DMM reading in step 8. If the 80T-150U/DMM reads lower, add the difference to the 80T-150U/DMM reading in step 8. 7. Remove the 80T-150U probe from the lag bath and insert it down into the COM input terminal on the Fluke 78, making contact at the bottom. 8. Select the temperature function on the Fluke 78, °C or °F to match the 80T-150U. Allow the readings to settle. The flashing reading of the Fluke 78 should be within 3 °C or 5.5 °F of the 80T150/DMM reading after taking into account the reading difference noted in step 6.

DMM

THERMOMETER
mV

80T-150U

TEMPERATURE PROBE

80T-150U

°C

°F

OFF

IMMERSED TO APPROXIMATELY SAME DEPTH

LAG BATH (ROOM TEMPERATURE WATER)
zr07f.eps

Figure 3-3. Ambient Temperature Lag Bath

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3-24. RPM80 Inductive Pickup Test (Optional Accessory) To test the RPM-80 inductive pickup, a triangle wave from a Function Generator will simulate automobile spark plug signals on a loop of wire containing a 10-ohm resistor. The pickup will be clamped to the wire, and output voltage from the pickup will be monitored by an oscilloscope.
To test the RPM80 Inductive Pickup, proceed as follows, referring to Figures 3-4 and 35 as necessary: 1. Solder a 10-inch piece of 14 or 16-AWG wire to one end of the 10-ohm resistor. 2. Connect the other end of the resistor to th