Troubleshooting For Circuit Faults
Troubleshooting For Circuit Faults
Ideally, most people would like electrical or electronic products and devices to be “breakdown-proof,” but unfortunately this is not possible. Most breakdowns are probably—directly or indirectly—a result of operating abuse or lack of maintenance.
Electrical or electronic breakdowns can be categorized by some very basic causes as follows:
- Dirt and contaminants
- Abnormal or excessive movement
- Poor installation
- Manufacturing defect
- Animals and rodents
Whenever too much heat is applied to electrical or electronic devices, problems occur. Heat increases the resistance of circuits, which in turn increases the current. Heat will cause the materials to expand, dry out, crack, blister, and wear down much more quickly; sooner or later, the device will break down.
Moisture will also cause circuits to draw more current and eventually break down. Moisture (water and other liquids) causes expansion, warping, quicker wear, and abnormal current flow (short circuits).
Dirt and other contaminants, such as fumes, vapors, abrasives, soot, grease, and oils, are materials that cause electrical and electronic devices to “clog” or “gum” up and operate abnormally until they finally break down.
Abnormal or excessive movement can lead to breakdowns. Vibrations and physical abuse are the leading causes of these types of breakdowns.
Poor installation is often the work of an unqualified installer or one who is careless or in a hurry. Failure to tighten a bolt or properly solder a connection results in an electrical or electronic device’s breaking down prematurely.
Manufacturing defects are also very common. For example, it is not uncommon to find a loose circuit board after delivery and installation. The shipping and transporting can also loosen or damage circuit boards and components.
Animals and rodents can also be the cause of electrical or electronic breakdowns. A rat or other small rodent may have chewed on an electric wire or found its way into a motor.
Circuit Fault Types
It is essential that every troubleshooter understand the four most common causes of circuit faults:
- Short circuit
- Open circuit
- Mechanical fault
Torubleshooting For Short Circuit
Basically, a short circuit results when the current takes a direct path across its source. For example, a short circuit in an electric motor is caused by a defect in the motor in which two wires of the circuit touch and cause a bypassing of the normal current flow.
Short circuits draw more current because the resistance in the circuit decreases; as a result, the voltage decreases. Typical signs of short circuits are the following:
- Blown fuses
- Increased heat
- Low voltage
- High amperage
Troubleshooting For Open Circuit
An open circuit results from an incomplete circuit. For example, an electric motor with an open circuit can be caused by a break in the motor circuit, which prevents the current from flowing in a complete path.
An open circuit will have infinite (unlimited) resistance and zero current since its path has been broken. Typical signs of an open circuit are (1) infinite resistance, (2) zero amperage, and (3) completely dead (inoperable) device.
Troubleshooting For Grounded Fail
A ground results when a defect in the insulation or placement of a wire or component causes the current to take an incorrect (abnormal) route in the circuit. For example, an electric motor with a grounded circuit results when part of the windings make electrical contact with the iron “frame” of the motor. A ground is theoretically similar to a short circuit; however, it has distinct characteristics. Generally, the short circuit causes the device to stop operating and trips a circuit breaker due to the direct bypass. However, in the grounded circuit, the device often keeps operating due to the indirect circuit bypass, but it operates poorly and draws abnormal currents and voltages. The grounded circuit also can be the most dangerous, since the device often keeps functioning; the operator can experience shocks, especially without proper ground-fault interrupters.
Common grounds result from wires with poor insulation, pinched wires, or misplaced components. Shocks are obtained from a grounded motor because the frame of the motor and the operator have become part of the electric circuit. Typical signs of a ground are as follows:
- Abnormal amperage reading
- Abnormal voltage reading
- Abnormal resistance reading
- Abnormal circuit performance
- Tripped ground-fault interrupters
- Periodic blown fuses or circuit breakers
Troubleshooting For Mechanical problems
Mechanical problems are a result of too much friction, wear, abuse, or vibration, where the physical part of an electrical or electronic device causes the breakdown. Broken belts, worn bearings, loose bolts, worn contacts, damaged chassis, and broken controls are common examples of mechanical problems. Typical signs of mechanical problems are as follows:
- Noisy operation
- Abnormal operation
- Visual clues
- Circuit failure
The most important tool or instrument a troubleshooter can use is his or her own senses. Most troubleshooting problems can be found by the use of one or all of the main senses: sight, smell, touch, and hearing.
Before any sophisticated attempt is made to analyze a problem, first visually look for an obvious cause. A cracked circuit board, broken wire, burned or charred component, or any type of damaged item can quickly lead the troubleshooter to the problem.
To the troubleshooter, there is not a more identifiable smell than that of a burned transformer. A good troubleshooter should easily be able to recognize this smell. Also, burned cables, insulation, wires, and components can give obvious clues to circuit faults and help isolate the main cause. Many troubleshooters rely on their sense of touch to locate component faults. Integrated circuits (ICs) should never be hot when touched. A hot IC would indicate a short circuit in the IC. Likewise, a hot, smoky motor is a common sign of a short circuit. On the other hand, a 10-watt (W) line resistor should not be cold when touched; it should feel warm or hot. This cold resistor would indicate an “open” component. Through experience, troubleshooters learn that different components tend to have degrees of temperatures unique to them and the specific operating environment. When you learn to recognize these differences, troubleshooting defective components will become easier.