Fluke 78 Service Manual
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Fluke 78 Service Manual

For iec 61010 cat ii meters only
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®
78
Automotive Meter
Service Manual
For IEC 61010 CAT II Meters Only
PN 666617
November 1998
© 1998 Fluke Corporation, All rights reserved. Printed in U.S.A.
All product names are trademarks of their respective companies.

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  • Page 1 ® Automotive Meter Service Manual For IEC 61010 CAT II Meters Only PN 666617 November 1998 © 1998 Fluke Corporation, All rights reserved. Printed in U.S.A. All product names are trademarks of their respective companies.
  • Page 2 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...
  • Page 3 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.
  • Page 4 • 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.

  • Page 5: 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. Functional Block Description ............... 2-3 2-3.
  • Page 6 Service Manual 3-1. Introduction ................... 3-3 3-2. Recommended Equipment ..............3-3 3-3. Operator Maintenance ................3-3 3-4. Case Disassembly ................3-3 3-5. Battery Replacement ................. 3-3 3-6. Fuse Test ................... 3-5 3-7. Fuse Replacement ................3-5 3-8. Circuit Assembly Removal ............... 3-5 3-9.
  • Page 7 3-10. DC and AC Current Test ..................3-12 3-11. Functional Description of Power Supply Components ........... 3-19 3-12. Voltage Levels ......................3-19 4-1. Fluke 78 Final Assembly ..................4-5 4-2. A1 Main PCA ......................4-7 5-1. Signal Abbreviations ....................5-3...
  • Page 8 Service Manual...
  • Page 9 4 V Range Simplified Schematic................2-5 2-3. 400 Ohm Range Simplified Schematic ..............2-6 2-4. A/D Converter ......................2-8 3-1. Disassembled Fluke 78 .................... 3-6 3-2. Display........................3-8 3-3. Ambient Temperature Lag Bath ................3-13 3-4. Setup for RPM80 Inductive Pickup Test ..............3-15 3-5.
  • Page 10 Service Manual...

  • Page 11: Introduction And Specifications

    Chapter 1 Introduction and Specifications Title 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...
  • Page 12 Service Manual...

  • Page 13: Introduction

    • 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.

  • Page 14: Conventions

    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.
  • Page 15 Output: Pulse to trigger Fluke 78 Thermocouple Type: K (Chromel vs. Alumel) (Fluke 80PK1) Not suitable for immersion in liquid. Accuracy: ±1.1°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).
  • Page 16 Service Manual Table 1-1. Specifications (cont) Function Range Resolution Accuracy Burden Voltage (Typical) AC Volts* 4.000 V 0.001 V ± (2.5%+2) (45 Hz to 1 kHz) 40.00 V 0.01 V ± (2.5%+2) 300.0 V 0.1 V ± (2.5%+2) 300 V ±...
  • Page 17 Introduction and Specifications Specifications Table 1-1 Specifications (cont) Frequency Counter Sensitivity and Trigger Level Input Range Minimum Sensitivity Approximate Trigger Level (Rms Sine Wave) (DC Volts Function) 1 Hz to 5 Hz 5 Hz to 20 kHz 400.0 mV dc 400 mV 4000 mV dc 400 mV...
  • Page 18 Service Manual...

  • Page 19: Theory Of Operation

    Chapter 2 Theory of Operation Title Page 2-1. Introduction .................... 2-3 2-2. Functional Block Description..............2-3 2-3. Circuit Descriptions................2-4 2-4. Input Overload Protection..............2-4 2-5. Rotary Knob Switch................2-4 2-6. Input Signal Conditioning Circuits ............ 2-4 2-7. Volts Functions................2-4 2-8.
  • Page 20 Service Manual...

  • Page 21: Introduction

    Theory of Operation Introduction 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.

  • Page 22: Circuit Descriptions

    Service Manual 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.

  • Page 23: Ohms Function

    Theory of Operation Circuit Descriptions R1+RT1 Ω 9.996M 4 VAC ACTIVE HIGH FILTER 1.1111M CONVERTER 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.

  • Page 24: Continuity

    Service Manual 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.

  • Page 25: Diode Test Function

    Theory of Operation Circuit Descriptions 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;...
  • Page 26 Service Manual BUFFER INTEGRATOR COMPARATOR REFER TO WAVEFORM INPUT – VOLTAGE – – COMPARE CONTROL VOLTAGE REFERENCE 131.072 kHz CLOCK SWITCH AUTO INTE- READ READ HOLD ZERO GRATE +INPUT –INPUT MICROCOMPUTER INTEGRATE RAMP READ ZERO HOLD RAMP BASELINE 16.7 AUTO ZERO 8.33 REPEAT SAMPLE #1...

  • Page 27: Frequency Measurements

    Theory of Operation Circuit Descriptions 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.

  • Page 28: Beeper

    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 + 3.7 ±0.2...

  • Page 29: Maintenance

    Chapter 3 Maintenance Title Page 3-1. Introduction .................... 3-3 3-2. Recommended Equipment ..............3-3 3-3. Operator Maintenance ................3-3 3-4. Case Disassembly ................3-3 3-5. Battery Replacement................3-3 3-6. Fuse Test .................... 3-5 3-7. Fuse Replacement ................3-5 3-8. Circuit Assembly Removal ..............3-5 3-9.
  • Page 30 Service Manual...

  • Page 31: Introduction

    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.
  • Page 32 Voltage: 8 V peak DC offset voltage: 0-4 V Frequency: 10 Hz-20 kHz Frequency Accuracy: .002% 100 mV DC Voltage Range Fluke 20 Series, 70 Series or 80 Accuracy: 0.5% Series Resolution: 100 µ V Thermometer Accuracy: 0.2 °C @ Ambient...

  • Page 33: Fuse Test

    Maintenance Operator Maintenance 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.
  • Page 34 SCREW #2-14X3/8 CONTACT, ANNUCIATOR SPRING TRANSDUCER CASE, BOTTOM 4 X FOOT, NON-SKID 4 X SCREW 5-14X3/4 KNOB ASSEMBLY SPRING DETENT MASK,BRACKET SWITCH, MOMENTARY BRACKET, LCD SHAFT, KNOB SHOCK ABSORBER MASK,BRACKET LCD ASSEMBLY KNOB ASSEMBLY zr05f.eps Figure 3-1. Disassembled Fluke 78...

  • Page 35: Cleaning

    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.)

  • Page 36: Display Test

    Service Manual 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.

  • Page 37: Ac Voltage Test

    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.

  • Page 38: Frequency, Dwell, And Duty Cycle Trigger Level Test

    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.

  • Page 39: Ohms Test

    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.

  • Page 40: Diode Test

    Service Manual 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.
  • Page 41 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 80T- 150/DMM reading after taking into account the reading difference noted in step 6.

  • Page 42: Rpm80 Inductive Pickup Test (Optional Accessory)

    Service Manual 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.
  • Page 43 Maintenance Performance Tests OSCILLOSCOPE FUNCTION GENERATOR Ω OUTPUT RESISTOR WIRE LOOP (14 AWG) INDUCTIVE PICKUP zr08f.eps Figure 3-4. Setup for RPM80 Inductive Pickup Test 3-15...
  • Page 44 Service Manual OSCILLOSCOPE DISPLAY OF TRIANGLE WAVE 3V P-P µ OSCILLOSCOPE DISPLAY OF INDUCTIVE PICKUP OUTPUT 5.7V 10 ms zr09f.eps Figure 3-5. Typical Waveforms for Inductive Pickup Test 3-16...

  • Page 45: Calibration

    5 times. 4. Set the DC Voltage Calibrator for an output of +3.5 V dc. 5. The Fluke 78 should display 3.500 V dc +/- 0.001. If necessary, remove the four case screws and case top and adjust R26. R26 (ADJUST FOR 3.500V DC ±...

  • Page 46: Troubleshooting

    3-26. Troubleshooting The procedures provided in these paragraphs will help isolate problems with the meter. When troubleshooting the Fluke 78 Automotive Meter, follow the precautions listed on the "Static Awareness" sheet to prevent damage from static discharge. 3-27. Surface Mount Assemblies The Fluke 78 Automotive Meter incorporates surface-mount technology (SMT) on the printed circuit assembly (pca).

  • Page 47: Common (Shunt) Regulator Troubleshooting

    Maintenance Troubleshooting Table 3-11. Functional Description of Power Supply Components Component Function Power supply startup device. Q8 provides Q7 base startup current. Q8 is always off during meter operation. VR1 provides the system reference voltage. It is used for the a/d converter reference and as a reference for both power supply regulators.

  • Page 48: Vdd (Series) Regulator Troubleshooting

    Service Manual 2. If Vrefh is correct, measure the voltage at U1 pin 6 (PS1). If Vps1 is not equal to 0 V +/-0.15 V, check R34 and R35. If Vps1 is still at an incorrect voltage, U1 is bad. 3.

  • Page 49: List Of Replaceable Parts

    Chapter 4 List of Replaceable Parts Title Page 4-1. Introduction .................... 4-3 4-2. How to Obtain Parts ................4-3 4-3. Manual Status Information..............4-3 4-4. Service Centers..................4-4 4-5. Parts Lists ....................4-4...
  • Page 50 Service Manual...

  • Page 51: Introduction

    Introduction 4-1. Introduction This chapter contains an illustrated list of replaceable parts for the Fluke 78 Automotive Meter. Parts are listed by assembly; alphabetized by reference designator. Each assembly is accompanied by an illustration showing the location of each part and its reference designator.

  • Page 52: Service Centers

    4-5. Parts Lists The following tables list the replaceable parts for the 78 Automotive Meter. Parts are listed by assembly; alphabetized by reference designator. Each assembly is accompanied by an illustration showing the location of each part and its reference designator. The parts lists give the following information: •...
  • Page 53 List of Replaceable Parts Parts Lists Manual Status Information Ref or Option No. Assembly Name Fluke Part No. Revision Level Main PCA 919709 Table 4-1. Fluke 78 Final Assembly Reference Description Fluke Notes Designator Stock Number *MAIN PCA BT 1...
  • Page 54 Service Manual MP28 FLUKE 78 T&B VIEW XA11C.EPS Figure 4-1. Fluke 78 Final Assembly...
  • Page 55 List of Replaceable Parts Parts Lists Table 4-2. A1 Main PCA Reference Description Fluke Note Designator Stock Number CAP, POLYES, 0.01 µF, ±10%, 1000 V 822361 CAP, CER, 3.3PF, ±0.25 PF, 1500 V, COJ 904636 C 3, 8 CAP, CER, 150PF, ±5%, 50 V, COG,0805...
  • Page 56 Service Manual FLUKE 78-4001 zr12f.eps Figure 4-2. A1 Main PCA...
  • Page 57 Chapter 5 Schematic Diagrams...
  • Page 58 Service Manual...
  • Page 59 Schematic Diagrams Table 5-1. Signal Abbreviations Number Name Description REFI REFerence Input AGND Analog GrouND REFH REFerence High plus power supply Power Supply 2 Power Supply 1 Power Supply 0 BIAS BIAS input Digital Output Port 2, bit 1 Diode Test Source OSCI OSCillator Input OSCO...
  • Page 60 Service Manual Table 5-1. Signal Abbreviations (cont) Number Name Description TEST TEST Port 0, bit 0 ClocK 1 ClocK 2 Icd backplane 1 Icd backplane 2 Icd backplane 3 Icd backplane 4 PUD* Power Up Digital output, active low Temperature Test RPM function input Function bit 0 Function bit 1...
  • Page 61 Schematic Diagrams FLUKE 78-4001 zr12f.eps Figure 5-1. A1 Main PCA...
  • Page 62 Service Manual FLUKE 78-1201 (1 of 3) zr13f.eps Figure 5-1. A1 Main PCA (cont)
  • Page 63 Schematic Diagrams FLUKE 78-1201 (2 of 3) zr14f.eps Figure 5-1. A1 Main PCA (cont)
  • Page 64 Service Manual FLUKE 78-1201 (3 of 3) zr15f.eps Figure 5-1. A1 Main PCA (cont)

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