TABLE OF CONTENTS Substitution and fault insertion
"Remove and conquer"
"Circle the wagons"
Trapping
Consultation
Intuition and out-of-the-box thinking
The previous chapter discussed logical/analytical frameworks for troubleshooting. While these frameworks work most of the time, some problems require less systematic techniques to complement the logical frameworks. Normally, you will begin to use these other techniques only after the logical analysis has failed to suggest a viable solution. Defining the problem, gathering information, and performing analysis still take place when you use these methods.
You may need to approach troubleshooting from a different point of view because a system may be too complex or sophisticated to troubleshoot with the knowledge available to you. This can occur with microprocessor-based equipment consisting of multiple components (such as a PLC or a DCS). Sometimes manufacturers provide only limited information about what goes on inside the equipment. Maybe the problem is transient in nature, or is in a complex system with communication links between components and multiple power systems and grounds, as in a multiple variable-speed drive system.
The substitution method is troubleshooting by substituting a known good component for a suspected bad component. For modularized systems or those with easily replaceable components, substitution may reveal the component that is the cause of the problem. First, define the problem and gather and analyze as much information as you can. Note that these steps are no different than the initial steps in the structured framework methodology. Then select a...
