Circuit Analysis and Troubleshooting

1
Circuit Analysis and Troubleshooting

• A Six Step Procedure
• Created by Jimmie Fouts
• Houston County Career Academyfor

2
Essential Question

• How can a standardized approach toward electronic
  equipment troubleshooting save many hours of
  equipment downtime and costly repairs?

3
A Six Step Procedure?

• A standardized approach toward electronic
  troubleshooting and maintenance
• Prevents equipment down time
• Saves time needed for repairs when required
• Ensures operation to design standards
• Saves money!

4
The SIX-STEP Procedure

• Use of a six-step procedure will provide a
  logical approach to trouble analysis
• The six-step procedure is as follows
• 1. Symptom recognition
• 2. Symptom elaboration
• 3. Listing of probable faulty functions
• 4. Localizing the faulty function
• 5. Localizing trouble to the circuit
• 6. Failure analysis

5
1. Symptom Recognition

• Determine if the equipment is functioning as
  designed. Is it normal or abnormal?
• A trouble symptom is a sign or indicator of a
  malfunction
• Use your senses of sight and hearing! Indicator
  lights, speakers, meterssmoke!
• Look for degraded performance as well degraded
  performance often leads to equipment failure
• Know your equipment!

6
2. System Elaboration

• Observe any built-in indicators for more
  detailed information on symptoms
• Obtain a detailed description of any trouble
  symptoms
• Similar symptoms can be caused by similar faults!
• Check front panel switches and control settings
• What fault is probably causing the specific
  symptoms in question?

7

• Symptom elaboration requires an evaluation of all
  observed displays
• Indications must be evaluated in relation to each
  other as well as the overall operation
• Record information observed! For example How did
  each control affect an associated meter or other
  indicator?
• Think about the information before jumping to a
  conclusion!

8
3. List Probable Faulty Functions

• Many equipments have more than one functional
  area or unit
• Where can the trouble logically be in order to
  produce the information gathered?
• For example Your computer contains RAM, a
  motherboard, a processor, a power supply, a hard
  drive.. What functional area might be at fault?
• Dividing the equipment into functional areas can
  save numerous trouble shooting steps

9
Functional Block Diagram!

• Useful in the isolation of a fault!
• Example
• Microphone Converts sound energy into electrical
  energy at an audio frequency
• Modulator Amplifies the audio signal and sends
  it to the transmitter to change the carrier
  signal to be modified
• Transmitter Provides an amplified radio
  frequency (RF) signal to the antenna assembly
• Antenna Assembly Converts the electrical RF
  signal into an electromagnetic energy for
  transmission. It also receives electromagnetic
  energy and converts it into an RF signal for the
  Receiver Unit
• Receiver Unit Converts received RF signal into
  sound
• Power Supply Converts alternating (AC) voltage
  into suitable direct current (DC) for operation
  of the various units

10
4. Localizing the Faulty Function

• Up to this point, no test equipment has been
  required only the equipment controls and
  indicators have been used
• You can probably make a decision on where the
  most probable area for the malfunction is
• Knowledge, skill, and proper test equipment
  should now be used to isolate the faulty
  functional area

11
Consider the Following Factors!

• Which functional unit will give the best
  information for eliminating other units?
• Which test points are more easily accessible?
• What past experience and history do you have
  concerning similar faults with this particular
  equipment?
• Are there other external units that may prevent
  proper operation of this unit?

12
5. Localizing Trouble to the Circuit

• More extensive troubleshooting is now required
  within the identified faulty unit
• Isolate circuits within the faulty unit
• Circuits and stages in circuit groups perform
  basic sub-function vital tasks
• Look for improper voltages, improper waveforms,
  obvious component overheating
• Isolate the defective circuit group!

13
6. Failure Analysis

• Steps 1 and 2 were used to recognize, verify, and
  obtain descriptive information
• Step 3 allowed you to make a logical selection of
  the logical faulty unit
• Step 4 provided for simple input-output tests and
  localized the faulty functions
• Step 5 localized the fault to the circuit within
  the faulty unit
• Step 6 will involve the actual replacement or
  repair of faulty circuit components

14
Schematic Diagrams

• Illustrate the detailed circuit arrangement of
  electronic parts that make up complete circuits
• Parts are represented symbolically
• Show what is inside the blocks of the block
  diagram
• Often provide voltage and resistance charts
• Actual faults can generally be traced to one or
  several individual parts resistors, capacitor,
  transistors, etc.

15
Complete, Degraded, Intermittent

• Complete or abnormal performance of a component
  usually results in equipment failure
• Degraded performance is the result of equipment
  not operating as designed or to design
  specifications
• An intermittent part malfunction refers to
  something that stops operating, then begins
  operating again

16
Isolation of Faulty Parts

• Observe the output signal of the circuit group
• Voltage, duration, waveform shape
• Conduct a visual inspection of parts and leads in
  the circuit
• Look for burned parts or defective connections
• Perform resistance checks
• Ensure ALL power sources are OFF to the unit
• Dont expect identical readings to the schematic.
  Tolerances of as much as 20 may be acceptable.
• Some equipments may require specialized test
  equipment. Refer to the Maintenance Manual.

17
BE AWARE of MULTIPLE FAULTS!

• Often active components fail because of other
  components within the circuit
• Common causes of failures may include
• Biasing resistor value changes causing a
  defective transistor
• Defective capacitors failing to block DC current
• Power surges from a power supply may cause
  burn-out of system components
• Excessive current usage causing defective fuses
• Intermittent faults that cause random failure

18
Return of Equipment to Operation

• After replacing the faulty part or components
  always recheck equipment for proper operation!
• Record your actions.they may be needed for
  future repairs!