Electrical troubleshooting basic tips and fault cataloging

Effective electrical troubleshooting must be conducted in an orderly fashion. A practical, systematic approach is the key. There are several troubleshooting methods, but any troubleshooting method is a combination of all or most of the following basic techniques:

• Thorough knowledge of the system and operation of the components.
• Visual inspection and simple operational tests without tools.
• Comparison of operation with another properly operating system.
• Circuit analysis using schematics and test equipment.
• The halving principle: localizing the fault within a few components by the process of successive elimination.
• Substitution of easily replaced components.
• Use of troubleshooting records (or log) of past difficulties and how they have been overcome.

Basic tips

Observe the system and establish what it does or does not do. This will usually pinpoint which specific circuit is faulty.

Keep the most current set of the schematic diagrams available for use. Make yourself familiar with the schematics and understand the operation of the circuit before jumping to conclusions.

Use  troubleshooting reference charts provided in your OEM maintenance manual to identify and correct common problems associated with the machinery provided.

When checking continuity of a circuit, remember that the voltage on both sides of the closed contact should be the same. However, both sides of an open contact may also be at the same voltage (if another contact bypasses it).

Cataloging Faults

Faults can be catalogued into one of two categories:

1. A function that does not occur due to a discontinuity in the electrical system. Causes may include the following:

• loose wire
• bad contact
• defective coil or coil lead
• blown fuse

2. A function is performed the wrong way. This is due to the insertion of incorrect components or connections such as:

• wires touching each other
• broken down insulation due to dirt or foreign objects
• time delay setting is either too short or too long
• faulty field device giving the wrong information to the logic
• the possibility of a frozen contact also has to be considered, although it is very remote with modern relays

Although preventive maintenance reduces the probability of failures, it does not eliminate them completely. Shutdowns may also occur for other reasons than equipment failure. Jams, emergency stops, and other similar situations will initiate shutdowns. When this happens, the system must be returned to normal operation with as little delay as possible.

For more information on electrical troubleshooting, contact your Valmet representative for training options.