Fluke 78 Service Manual

®

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.

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	Fluke Europe B.V.
P.O. Box 9090	P.O. Box 1186
Everett WA	5602 B.D. Eindhoven
98206-9090	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:

∙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.

∙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:

∙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

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.	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.	Ohms Function ............................................................................	2-5
	2-9.	Continuity ....................................................................................	2-6
	2-10.	Temperature Function ..................................................................	2-6
	2-11.	Diode Test Function ....................................................................	2-7
	2-12.	RPM Function ..............................................................................	2-7
	2-13.	Current Function ..........................................................................	2-7
	2-14.	Analog Section of Integrated Multimeter IC (U1) ..........................	2-7
	2-15.	Frequency Measurements ............................................................	2-9
	2-16.	Dwell and Duty Cycle Measurements .........................................	2-9
	2-17.	Microcomputer Control ....................................................................	2-9
	2-18.	Peripherals to U1 ...............................................................................	2-9
	2-19.	AC Buffer .....................................................................................	2-9
	2-20.	AC converter .................................................................................	2-9
	2-21.	Active Filter ..................................................................................	2-9
	2-22.	A/D Converter ..............................................................................	2-9
	2-23.	Beeper ...........................................................................................	2-10
	2-24.	Power Supply ................................................................................	2-10
	2-25.	Display ..............................................................................................	2-10
3	Maintenance .........................................................................................		3-1

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	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.	Display Access ..................................................................................	3-5
	3-10.	Cleaning .................................................................................................	3-7
	3-11.	Performance Tests .................................................................................	3-7
	3-12.	Setup ..................................................................................................	3-7
	3-13.	Display Test ......................................................................................	3-8
	3-14.	DC Voltage Test ................................................................................	3-8
	3-15.	AC Voltage Test ................................................................................	3-9
	3-16.	Frequency Test ..................................................................................	3-9
	3-17.	Frequency, Dwell, and Duty Cycle Trigger Level Test ....................	3-10
	3-18.	RPM Test ..........................................................................................	3-10
	3-19.	Ohms Test .........................................................................................	3-11
	3-20.	Continuity Test ..................................................................................	3-11
	3-21.	Diode Test .........................................................................................	3-12
	3-22.	DC and AC Current Test ...................................................................	3-12
	3-23.	Temperature Test ..............................................................................	3-12
	3-24.	RPM80 Inductive Pickup Test (Optional Accessory) .......................	3-14
	3-25.	Calibration .............................................................................................	3-17
	3-26.	Troubleshooting ....................................................................................	3-18
	3-27.	Surface Mount Assemblies ...............................................................	3-18
	3-28.	Power Supply Related Troubleshooting ...........................................	3-18
	3-29.	Common (Shunt) Regulator Troubleshooting ..................................	3-19
	3-30.	Vdd (Series) Regulator Troubleshooting ..........................................	3-20
4	List of Replaceable Parts ....................................................................		4-1
	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
5	Schematic Diagrams............................................................................		5-1

ii

List of Tables

Table	Title	Page
1-1.	Specifications...........................................................................................................	1-5
2-1.	Typical Voltage Levels and Tolerance (Referenced to Common) ..........................	2-10
3-1.	Recommended Test Equipment...............................................................................	3-4
3-2.	DC Voltage Test ......................................................................................................	3-8
3-3.	AC Voltage Test ......................................................................................................	3-9
3-4.	Frequency Test.........................................................................................................	3-9
3-5.	Frequency, Dwell, and Duty Cycle Trigger Level Test ..........................................	3-10
3-6.	RPM Test .................................................................................................................	3-10
3-7.	Resistance Test ........................................................................................................	3-11
3-8.	Continuity Test ........................................................................................................	3-11
3-9.	Diode Test................................................................................................................	3-12
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

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iv

List of Figures

Figure	Title	Page
2-1.	Block Diagram.........................................................................................................	2-3
2-2.	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.	Typical Waveforms for Inductive Pickup Test .......................................................	3-16
3-6.	Calibration Adjustment Point ..................................................................................	3-17
4-1.	Fluke Final Assembly .............................................................................................	4-6
5-1.	A1 Main PCA ..........................................................................................................	5-5

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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

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1-2

Introduction and Specifications 1

Introduction

1-1. Introduction

This Service Manual provides information on maintaining, troubleshooting, and repairing the Fluke 78 Automotive Meter. This information includes the following:

∙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:

∙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.

∙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:

±([% of reading] + number of least significant digits)

1-4

		Introduction and Specifications		1
		Specifications
		Table 1-1. Specifications
	Maximum Voltage Between
	any Terminal and Earth	300 V
	Ground
	Fuse Protection
		15 A 600 V FAST Fuse
	Display
		Digital: 4000 counts, updates 4/s
		Bar Graph: 64 segments, update rate 40/s
		Frequency: 9,999 counts, updates 3/s
	Operating Temperature
		0°C to 55°C (32°F to 131°F)
	Storage Temperature
		40°C to 60°C (40°F to 140°F)
	Temperature Coefficient
		0.1 x (specified accuracy) per °C ambient
		(<18°C or >28°C). Temperature, 0.04% + 0.1°C per °C
	Relative Humidity
		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
		2000 meters maximum
	Electromagnetic Compatibility	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.
	Battery Type
		9 V, NEDA 1604 or 6F22 or 006P
	Battery Life
		Alkaline: 500 hrs (typical)
		Carbonzinc: 300 hrs (typical)
	Continuity Beeper
		4096 Hz
	Shock, Vibration
		Per MILT28800E for a Type III, Class 3 Style D, Instrument
	Size (HxWxL)
		1.12 in x 2.95 in x 6.55 in
		(2.8 cm x 7.5 cm x 16.6 cm)
	Weight
		12 oz (340g)
	Safety
		Complies with EN 610101:1993, ANSI/ISA S82.011994 and
		CAN/CSA C22.2 No. 1010.192 Overvoltage Category II.
	Safety Approvals
		CSA Certified, TUV Product Service licensed, UL
	EMI Regulation
		Complies with FCC Part 15, Class B, VDE 0871B, Vfg. 2431991
	Inductive Pickup
		Input: Magnetic field from spark plug
		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).
		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
	MIN MAX Recording
		Accuracy: Specified accuracy of measurement function ±16 digits for
		changes > 200 ms in duration (±52 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	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)	N/A
	300.0	V		0.1 V		± (2.5%+2)
	300 V			1 V		± (2.5%+2)
To 20 kHz	--			--		± 1.5 dB typical
DC Volts*	400.0 mV			0.1 mV		± (0.3%+5)
	4000 mV			1 mV		± (0.3%+1)
	4.000	V		0.001 V		± (0.3%+1)
	40.00	V		0.01 V		± (0.3%+1)	N/A
	300.0	V		0.1 V		± (0.3%+1)
	300 V			1 V		± (0.3%+1)
Resistance	400.0 J			0.1J		± (0.5%+2)	N/A
	4.000 kJ			0.001 J		± (0.5%+1)
	40.00 kJ			00.01 kJ		± (0.5%+1)
	400.0 kJ			000.1 kJ		± (0.5%+1)
	4.000	MJ		0.001 MJ		± (0.5%+1)
	40.00	MJ		0.01 MJ		± (1%+3)
Continuity	400.0 J			0.1J		Beeper on @	Open circuit voltage
						<30 J for	< 1.5 V
						short of
						1 ms or longer
Diode Test	2.500	V		0.001 V		± 2% typical	Open circuit voltage
							< 3.3 V
AC Current	10.00	A**		0.01 A		± (2.5%+2)	0.03 V/A
(45 Hz to 1 kHz)
DC Current	4.000	A		0.001 A		± (1.0%+5)	0.03 V/A
	10.00	A**		0.01 A		± (1.0%+2)	0.03 V/A

*Input impedance: 10 MJ (nominal), < 150 pF.

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

Function	Range	Resolution	Accuracy
Frequency	99.99	0.01 Hz	± 0.01%+2)
(1 Hz to 20 kHz)	999.9	0.1 Hz	± (0.01%+2)
	9.999 kHz	0.001 kHz	± (0.01%+2)
	20.00 kHz	0.01 kHz	± (0.01%+2)
(107 V-Hz maximum)	>20.00 kHz to 99.99 kHz	0.01 kHz	Usable
	500.0 kHz	0.1 kHz	Usable
RPM 1	70-7,000 RPM (usable to 9,999)	1RPM	± (0.2% + 2)
RPM 1	120-7,000 RPM (usable to 9,999)	1RPM	± (0.2% + 2)
Dwell Angle	0-120	1 degree	± 2 degrees
Duty Cycle	0.0-99.9%	0.1%	± (0.2% per kHz +0.1%)
	(1 Hz to 20 kHz, pulse width> 5 µs)		(for rise time <1 µs)
Temperature*	-40 to +999°C @ >20°C ambient,	1 degree	± (0.3%+6°C) @ -40 to -20°C
	to +980°C below 20°C ambient		± (0.3%+4°C) @ -20 to 0°C
			± (0.3%+3°C) @ 0 to 170°C
			± (0.3%+5°C) @ 170 to 260°C
			± (0.3%+6°C) @ 260 to 700°C
			± (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		1
				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
	4.00 V	0.7 V	0.3 V	1.7 V
	40.00 V	7 V	3 V	4 V
	300.0	70 V	30 V	40 V

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1-8

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.	Ohms Function ..............................................................................	2-5
2-9.	Continuity ......................................................................................	2-6
2-10.	Temperature Function....................................................................	2-6
2-11.	Diode Test Function ......................................................................	2-7
2-12.	RPM Function................................................................................	2-7
2-13.	Current Function............................................................................	2-7
2-14.	Analog Section of Integrated Multimeter IC (U1) ............................	2-7
2-15.	Frequency Measurements ..............................................................	2-9
2-16.	Dwell and Duty Cycle Measurements ...........................................	2-9
2-17.	Microcomputer Control .....................................................................	2-9
2-18.	Peripherals to U1................................................................................	2-9
2-19.	AC Buffer ......................................................................................	2-9
2-20.	AC converter..................................................................................	2-9
2-21.	Active Filter ...................................................................................	2-9
2-22.	A/D Converter ...............................................................................	2-9
2-23.	Beeper ............................................................................................	2-10
2-24.	Power Supply.................................................................................	2-10
2-25.	Display ...............................................................................................	2-10

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2-2