about fault finding techniques

3. Learning aim B:
Examine fault finding techniques and test plans used
when measuring and testing electronic circuits.
B.P2 Explain two suitable techniques for testing faults in given
analogue and digital circuits.

4. Learning Objective :
After end of the session trainees will be able to
understand Visual fault finding technique
• Definition of Fault finding
• Visual Examination technique.
• What is the visual inspection method and how it is useful for fault finding.
• Types of faults
• Visual inspection method using oscilloscope.

5. Definition of the Fault
Fault finding means the testing of the operation
of electrical equipment to determine if that
electrical equipment is safe and working correctly
as per the given circuit diagram.

6. Visual Inspection technique:
• Visual Inspection, or Visual Testing (VT), is the oldest and most basic method
of inspection.
• It is the process of looking over an electronic circuit using the naked eye to look
for flaws.
• It requires no equipment except the naked eye of a trained inspector.
• It is most important test you will conduct and should be undertaken before any
power supply to the board. In this technique many faults can identified.
• Basic aids: Magnifier and oscilloscope
• The main purpose of the Visual Inspection method is
• Burnt ,damaged or broken
• All components are present
• At correct location
• Placed in the correct orientation
• Have good solder joints

7. In case of PCB boards Visual Inspection method need to be performed on both
side of the PCB.

8. Types of faults identified with Visual
Inspection.
•Short circuit faults
•Open circuit faults
•Component polarity
•Component value

9. Short circuit faults
• Short circuit fault is an electrical connection between two or more points
these points can either be components pins or tracks on PCB.
• These short circuit connections because of wrong soldering by the
manufacture or designer. These faults can be identified visually also used
suitable measuring equipment's like DMM and Oscilloscope and Logic probe.
• The following figures shows the short circuit it can be found visual
inspection. Short circuit in the tracks of the PCB board or bread board.

10. Open circuit faults
• The open circuit two points which should be connected or not.
• These fault can be identified visually with help of schematic and
routing diagram or using electrical tests also used suitable measuring
instrument like DMM, Oscilloscope and logic probe.
• Switch is the example of open circuit or closed circuit.

11. Components polarity
• Component polarity faults are where a
polarity sensitive components has been
placed in the wrong orientation
• Example
• LED placed backward
• These type of faults are can be identified
using visual inspection methods along
with comparing with datasheet and
placement diagram.

12. Component values
• A component value fault is where the correct
type if component has been used. But the value
sis wrong.
• Example
• 10K resistor is used instead of 330R
• 1uF us used instead of 1nF
• These faults can identified visually and With help
of magnifier .
• A magnifying glass can only help us to identify
errors in connection of devices, implementation
of design, and in model number of devices.
• If this type of error exists it can be removed by
making changes in device connection, model
number, and reimplementation of design.

13. Oscilloscope
• Oscilloscope provides a detailed and in-
depth visual examination of waveform and
its properties.
• Using this oscilloscope, we will analyze
voltage waveform at each node of the
circuit like transformers’ primary and
secondary, bridge diodes, capacitor filters,
voltage regulator and output terminals to
make sure properties of voltage waveform
is as per the required output at each node.
• If the properties of the waveform do not
meet our requirement then we will make
necessary changes in the circuit.