Introduction To Line Telecommunications

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17. Fault Finding And Troubleshooting


17. - Fault Finding And Troubleshooting


17.1 - Verification Of The Fault


17.2 - Guidelines To Resolving A Fault

17.3 - Reporting A Fault To The Manufacturer

17.4 - Little Green Men And Other Gremlins

17.2 - Guidelines To Resolving A Fault

In the majority of cases the inspection above will reveal the cause and hence the action required to resolve the fault.

There will be occasions when this inspection will reveal nothing and the fault cannot be reproduced to order. This is usually the result of an intermittent fault or a fault whose cause is external to the system. These are the most difficult faults to resolve and require the investigation to taken further.

Assume that the fault exists until it has been established that the occurrence was an isolated incident and that the system is functioning correctly.

17.2.1 - Determine Possible Causes

At this stage in the investigation process time should be taken to consider the results obtained so far. It may be necessary to recheck some findings and repeat some tests.

Look at the environment in which the system is installed. Pay attention to the physical layout, nearby machinery or equipment which may be having an effect on the system or its components. Consider each possibility in isolation and in conjunction with the others. ‘Nearby’ will include adjacent buildings and possibly the premises of neighbouring people.

It will also be useful to seek the advice of colleagues and question the customer further regarding the reported fault and its circumstances.

17.2.2 - Eliminate Possible Causes

Examine the possible causes that have been identified and asses each for its effect on the system. In the case of equipment this should be switched on and used in its normal manner to determine if there is any detrimental effect to the system. If there are multiple pieces of machinery or equipment listed as possible causes then try varying combinations.

If the precise source cannot be determined then prioritise the candidates in order from most probable to least probable, leaving out any that have been eliminated.

Should this lead to a specific source of the fault being identified then work can begin to eliminate its effect. With an intermittent equipment fault the affected units can be replaced or if the source is external then shielding and screening may be required.

17.2.3 - Substitution of Equipment

If the cause is still not apparent, but the fault persists then the equipment should be assumed suspect and substituted piece by piece in an attempt to remove, by elimination, the defective component.

Before starting, use the fault report to list by probability, all the connected equipment. Use this list to swap out the most likely candidates first. Since this will usually involve the system to be powered down for central items consideration must be shown to the customer and a convenient time decided upon. Should there only be a single opportunity to power down the system then all components which need this to be swapped must be swapped together. Bear in mind that this may affect the accuracy of the final diagnosis.

If the entire system as been replaced and the fault is still present the cause is almost certainly external and the list of probable causes will need re-assessment.

17.2.4 - Has The Fault Been Resolved By The Manufacturer

When a fault defies the investigation, check with the equipment manufacturer to see if they are aware of the type of fault and its possible causes. Do they have it under investigation ? Do they have a solution ? What advice can they give regarding possible causes ?

The engineering staff will have experienced a wide range of problems and it is wise to seek their advice as this can save a great deal of time and money.

If the fault is new then the manufacturer will usually begin their own investigation.



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Extracted from

Introduction To Line Telecommunications
Copyright Panasonic Business Systems UK Ltd 2000