TROUBLESHOOTING
system in detail and determine the paths of influence that could cause the malfunction. To troubleshoot a fault we need to understand how the system works in a normal operating mode. Only then can we understand in what ways the system is NOT operating properly. We then need to determine the paths of influence – all of the functions whose output, if not working, will cause the observed malfunction indication. There can be multiple paths of influence – they can be electrical, fluid (fuel or hydraulic), mechanical, or any combination of functional activities. The functions within those paths of influence can be: Supply Control Actuation Indication Distribution Protection Carrying Pumping For example, let’s say our widget system is controlled by
three different paths of influence – electrical, mechanical, and hydraulic.
Widget Electrical Mechanical Hydraulic We then need to examine each path of influence and
determine what the critical path is – that path that contains the actual cause of the defect. In the example, maybe we determine that the hydraulic system couldn’t cause the problem our widget system is experiencing. We then have two possible critical paths – electrical or mechanical.
Testing and Corrective Action Now that we understand our paths of influence and what our critical paths are, it is time to test. Since in our widget situation there are two possible critical paths, we need to determine which one is causing the problem. This is where we need to think about how to approach our testing to find our problem. We need to determine which path of influence is the problem. When testing, we need to consider time and difficulty when doing our tests. In this case, maybe a cannon plug which goes into the widget is easily accessible. We can disconnect it and test for continuity, voltage, or ground as needed. If we find it is faulty (let’s say we aren’t getting power at the cannon plug to the widget) we know the electrical path is the
BATTERY Figure 1 22
HelicopterMaintenanceMagazine.com June | July 2016 BATTERY BUSS CIRCUIT BREAKER
critical path we need to continue testing and can eliminate the mechanical path. We refer to the wiring diagrams and schematics we used to determine the electrical critical path to perform our tests. In this case, we know that our critical path contains the following components (See Figure 1). Some people like to work with a theory of halves –
keep testing at the halfway points until the problem is found. In our case, we don’t have power going into the cannon plug at the widget. So if we work with the theory of halves, we would go to, let’s say the control switch, and determine if we are getting power to the control switch. If we aren’t, we know that everything to the right of the control switch should be good, and we can work back towards the battery. We might check for power at the battery buss next. If that test shows we don’t have power going to the buss, we can then eliminate the circuit breaker. Further inspection reveals that there is a broken terminal at the battery buss. We take corrective action and replace the terminal. We then test the voltage at the buss and it checks good. We check the cannon plug at the widget and sure enough, we are getting proper voltage. We reconnect everything and perform an operational test and voila – the widget works. Problem solved! Sometimes the theory of halves isn’t necessarily the
quickest method of testing. Sometimes it depends on access to testing points. Say the control switch isn’t easily accessible, but the circuit breaker panel is. We may want to start there. After all, we are trying to discover the solution in the most efficient manner possible. Sometimes our choice where to begin testing doesn’t end up being the fastest method. For example, in the same widget situation, we test the control switch and determine we have good voltage going into it. We check the output voltage and find out it tests good. We then decide to test the voltage at the resistor and it also checks good on the input and output side. We then test the relay and find out it checks good. Upon further inspection of the cannon plug that connects to the widget, we determine that the pin has a loose crimp on the wire coming from the relay. We replace the pin and everything checks good. In this case, it would have been quicker if we would have just started working our way back from the connector. Even so, the time we took to test and find the problem is a lot less than the time and money it would have cost to take a shotgun approach. What about that guy that decided to just change the widget because “they always fail?” That didn’t fix the problem, so he decided to change out the relay because he knows how darn troublesome relays can be. That didn’t work. You know where this is going…….. If we hadn’t spent the time to understand the system and the paths of influence, this whole process could have taken a lot longer.
CONTROL SWITCH RESISTOR RELAY WIDGET
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