NORTH EET 160 - Chapter 5- Circuit Troubleshooting Four Sections

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Slide 1 Chapter 5:Circuit TroubleshootingFour Sections ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 2 2Troubleshooting• Troubleshooting is the process whereby you diagnose a malfunctioning system and identify the specific defect.• Once the defect is identified, a judgment must be made regarding the feasibility of repair– Time, cost, etc.• This chapter examines troubleshooting strategies and techniques. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 3 35.1a Troubleshooting Series Circuits• Pure series circuits are rare in practical electronic systems.• Troubleshooting strategies applicable to series circuits play a major role in troubleshooting advanced circuit configurations. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 4 4Basic Concepts• Logical troubleshooting procedures will aid in analyzing and troubleshooting all circuits, simple or complex.• Three goalsas a troubleshooter should be:– Make a measurement only if you know what a “good” reading would be.– Make as few measurements as possible.– Select the best tool for the task at hand.• Know what is normal in a circuit.– Schematic– Known good circuit for comparison– Intuitive understanding ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 5 5Intuitive Troubleshooting• Developing a solid intuitive understanding of circuit behavior is important in becoming a skilled troubleshooter.• There are some general rules that form the basis for all troubleshooting efforts.• The effects of defective power supplies, open circuits, short circuits, and components whose values have changed are important to understand. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 6 6Effects of an Open Circuit• Open circuits are characterized by having infinite resistance.• An open circuit will appear to have the applied voltage across it.• If the open circuit appears between a monitored point and ground, the meter will read the source voltage; otherwise it will be zero.If the circuit is open, how much current is flowing? 0How much voltage will be dropped across each resistor? 0What voltage will be measured across the open? The PS 25v ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 7 7Effects of a Short Circuit• A short in a circuit is characterized by having zero resistance, or very low resistance.• When a short circuit occurs within a series component, other components in the series will have higher currents.• The voltage across a short circuit is zero.•The best tool for diagnosis is a VOMR across R4= 0 ΏE across R4= 0 VI through the short = Current increases because R4is out of the circuit. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 8 8Effects of a Short CircuitWith R4 shorted there will be an increase in current. The blue arrows indicate larger voltages across every component because of increased current. Therefore the voltage read across every component (with respect to ground) will measure closer to the applied voltage.5.1a End ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 9 95.1b Effects of Component Tolerances• Because of aging or overheating, component values may change in an electrical circuit.• If a component has increased in resistance, then the effects would be similar to an open circuit.• If a component has decreased in resistance, then the effects would be similar to a short circuit. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 10 10Summary for Troubleshooting Series CircuitsType of Defect Voltage with Respect to Ground Voltage across Defect Voltage across Other Components Open Nearer or equal to supply terminal on same side of defect Full supply Zero Increased resistance Nearer or equal to supply terminal on same side of defect Increased Decreased Shorted Nearer or equal to supply terminal on opposite side of defect Zero Increased Decreased resistance Nearer or equal to supply terminal on opposite side of defect Decreased Increased ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 11 11Circuit Connectivity Problems• In practice, circuit boards can develop defects:–Opens–Shorts– Higher resistance– Lower resistance• When circuit board traces open or short they are very difficult to repair since they are often within the layers of the circuit board. •Options– Entire board is discarded– Miniature Component Repair Technicians can often repair.• High end equipment• Obsolete equipment


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NORTH EET 160 - Chapter 5- Circuit Troubleshooting Four Sections

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