For IEC 61010 CAT II Meters Only 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. 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)