A resource for safe and effective troubleshooting from the leaders in simulation training.
Welcome back, Troubleshooters! Today on Troubleshooting Thursdays, we’re presenting a recap of Tips 1 to 16—everything we’ve been learning for the last four months, all in one tidy package. (Call it “Troubleshooting Tips 101.”) If you’ve been following along with us since the beginning, this is a great summary of what you’ve learned. If you haven’t, this list will show you what you’ve missed, and where to find the material.
In this lesson, we explained the importance of troubleshooting, outlined Simutech Multimedia’s Systematic Troubleshooting Approach, and discussed how preparation is the key to success (and safety!). We then looked at the first step of our Systematic Troubleshooting Approach—observation—and saw that careful observation using all of your senses, along with a little bit of reasoning, can identify many defects in a circuit right away, with only minimal testing. Tips 2 through 7 cover the remaining steps.
The second step of our Systematic Troubleshooting Approach is to define the problem area, but that can be challenging. Using your observations, with the help of a schematic diagram, apply logic and reasoning to determine the specific problem area by eliminating all of the functioning areas.
The third step of our Systematic Troubleshooting Approach is to identify possible causes of the electrical fault. Write down each and every possible fault that could cause the problem, no matter how unlikely.
This is the second part of Step 3. Once you have a complete list of the possible causes, then next step is to rank them in order of how probable they are. Most often, there is one faulty component, and so components should be checked in this order: 1) components that burn out or wear out; 2) coils, motors, transformers and other devices with windings; 3) loose connections; 4) defective/incorrect wiring.
Once you have determined the most probable cause, you must perform tests to prove it is in fact the cause, or to rule it out. (WARNING: The electrical energy contained in many circuits can be enough to injure or kill! Make sure you follow all of your company’s safety precautions, rules and procedures while troubleshooting.) Testing can be done with several different devices, particularly multimeters, which can be used on most electrical equipment. Remember to predict what the meter should read BEFORE taking the reading. Use the “divide and eliminate” method to efficiently eliminate parts of the circuit in the problem area until you isolate the defective component. After replacing the component, test all features of the circuit to make sure there are no other problems in the circuit.
When you know the cause of the problem, first lock out the circuit and verify it is dead, and then replace the component. Once the component is removed, test it to be certain it is defective. If it is not defective, go back to Step 2. When the defective component has been confirmed and replaced, test-operate the entire circuit to be sure there are no other faults contributing to the malfunction.
Once you have replaced the defective part and the circuit is working properly, it is valuable to figure out why the malfunction occurred, so that you can assess how likely it is to reoccur. Ask yourself these questions: Did the component fail because it was old? Did the environment where the equipment is located cause excessive corrosion? Are there wear points that caused the wiring to short out? Did the component fail because of improper use? Is there perhaps a design flaw in the component that caused the problem? Determining the answers to these questions can save your organization a lot of money.
In this lesson, we looked at the types of meters used for troubleshooting and their specific uses: voltmeters, ohmmeters, ammeters, and multimeters. Before using any of these meters, you should know what a normal reading should be, so if you get a different reading when testing a faulty circuit, you’ll know that that part of the circuit contains a fault. We also looked at a number of very important Dos and Don’ts for the safe testing of electrical circuits that you must know before using a meter.
In this TsT, we defined an electrical fault as “any abnormal electric current.” We then looked at the most common types of faults: open circuits and short circuits. Opens occur when there is a break in the circuitry, such as a broken wire, loose connection, etc. Shorts occur when two or more components that should not be touching come in contact with one another. Faults may also be a combination of the two.
Before testing for a fault, you must know whether the circuit should be live or dead while testing. Be sure to check your organization’s policy for testing on live circuits, because it can be very dangerous and is sometimes prohibited. Certain work procedures must be followed and protective equipment may be required. Simutech Multimedia’s training simulations allow for testing on both live and dead circuits.
This lesson covered testing for opens and open neutrals with a voltmeter, and featured two excellent teaching videos from our Troubleshooting Electrical Circuits module. Voltmeters are the best tool for finding open circuits IF you can safely turn the power on. In the first example, we showed you how to test for an open in a circuit in which the absence of voltage was the clue to where the problem lay (e.g., the voltmeter reading for the second switch was zero). In the second example, the open neutral, the presence of voltage on either side of the lightbulb in the circuit indicated that the problem was not in the lightbulb, but in the neutral wire.
This lesson described what an ohmmeter is (a tool for measuring resistance in circuits), when it is used, and the best practices for using one to find opens. It featured a teaching video from our TEC module demonstrating how to use an ohmmeter to test for an open in a malfunctioning circuit with a lightbulb. After locking out the circuit and verifying it was dead, we tested the most probable cause (the lightbulb). The reading of 26 ohms indicated the normal resistance of a lightbulb, meaning that the open was before the test point. We kept systematically dividing the circuit in half, eliminating the portions with normal tests, until we isolated the problem component for which the ohmmeter reading was zero.
In this TsT, we defined a short circuit (a fault that occurs when a portion of a circuit accidentally becomes connected to another portion of the circuit, causing improper operation). A teaching video from our TEC module demonstrates a short to ground (a short circuit that occurs when a part of the circuit, usually a conductive portion of a wire, comes into contact with a grounded object such as an enclosure). All circuits are protected by “overcurrent devices” such as fuses or circuit breakers, which open the circuit when a predetermined amount of current flows through them, thereby interrupting the flow of current. When this happens, you have to determine the cause, which may well be a short to ground.
This lesson looked at one method for finding shorts using an ohmmeter. We demonstrated this method using a sample malfunctioning circuit with a blown fuse. After locking out the circuit, verifying it was dead, and removing the fuse, we used the ohmmeter to test the part of the circuit from the load side of the fuse to ground. The low resistance reading indicated a short to ground, but the location was not obvious. To locate it, we kept dividing the circuit in half, keeping the black lead on the ground terminal, opening test points, and testing with the red lead, until we found the defective wire. Only then did we replace the fuse.
This lesson demonstrated a second method for finding shorts using an ohmmeter, using a circuit consisting of two series circuits in parallel, each containing three switches that must be closed in order to turn on a lightbulb. With the circuit locked and verified dead and the blown fuse removed, we began testing. (This method is different from the first in that the ohmmeter leads are left in the one location during the testing.) With the leads on the ground terminal and the load side of the fuse, the meter reads zero, indicating a short to ground somewhere in the circuit. Leaving the leads in place, we disconnected a wire at the half-way point in the circuit, and noted the meter reading, which remained zero. This told us that the short was in the second circuit, so we reconnected the wire and disconnected another at switch 4, at which point the meter read 26 ohms. This result indicated that the short must be located between the open point and the lightbulb. We systematically divided the problem area in half, disconnecting and reconnecting the wires, and noting the meter readings, until we located the defective wire.
In this TsT, we talked about the key points to remember when testing circuits. Most of these are safety measures, so they are very important! It’s critical to keep revisiting these points until they become second nature. Electricity can be deadly, so make sure you take all of the necessary precautions and follow your organization’s safety policies. In addition to safety measures, we looked at some basic points to remember when trying to diagnose malfunctions that will help you locate faults logically and efficiently.
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