Fault finding & diagnostics -
The problem is that the root cause is not always determined by this method, and whist the symptoms may be temporarily alleviated, if the component exchanged was not the cause of the issue but a symptom of it then sooner or later the trouble will come back.
The second method is to use inspection and testing. This is the route we favour. It may cost a little more initially, as time is necessary to undertake this testing, however this will lead to correcting the root cause of the issue and identifying all the affected components. The method involves identifying the system affected then performing end to end testing, measuring the inputs, outputs and power supply to each device until the defective component is identified.
If a methodical step by step approach is followed the cause of an issue will ultimately always be found.