Page 68 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Power supplies-troubleshooting

Objectives: At the end of this lesson you shall be able to
• list the initial activities involved in troubleshooting
• list the three general steps involved in troubleshooting
• list and explain the two popular methods of troubleshooting
• list the possible defects in a power supply.

Introduction
Troubleshooting in any equipment or in a circuit involves the following activities:

– To identify the exact nature of the problem.
– To identify the section causing the problem.
– To isolate and arrive at the exact cause(s).
– To confirm the causes by necessary tests.

– To replace the problem-causing parts.
– To re-test and confirm the satisfactory working.
The following are the general steps involved in troubleshooting.
i Physical and sensory tests
– Look for the most common physical faults, such as broken wires, cracked circuit boards, dry solders and
burnt out components.
– Smell for hot or burning components.
– Feel with the fingers for unduly hot components.

ii Symptom diagnosis
Learn the operation of the system to be repaired with the help of its block diagram and its input and output
specifications.

Observe the symptoms produced by the defective system, and determine which section or function would produce
the symptoms.
iii Testing and replacing defective components

When the probable defective section has been diagnosed, check the probable components in that section of the
circuit that are most likely to go defective in the order given below:
Components should be checked in the order given below because that is the order in which they fall in most
cases.
– Active high power components: For example, components such as transistors, ICs, and diodes. High
power devices are physically large in size and are used for handling the high power, generally in output
circuits.

– Active low power components: These are the same as in (a) but are physically small and can handle smaller
amounts of power.
– High voltage/power passive components: Such components are resistors, capacitors, transformers, coils,
etc. which handle large amounts of voltage/power. They are found in power supplies and output circuits.
– Low power passive components: These are the same as in (c) but are physically smaller and handle
comparatively less power and are low in value (ohm, microfarad, microhenry, etc.)

Note: This procedure may not turn out to be true always. Hence, do not attempt to replace common
sense and meter measurements with the procedure.

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CITS : Power - Electrician & Wireman - Lesson 60-69