Transcript Circuit Analysis And Troubleshooting PowerPoint

Circuit Analysis and
Troubleshooting
A Six Step Procedure
Created by Jimmie Fouts
Houston County Career Academy
for
Essential Question
• How can a standardized approach toward
electronic equipment troubleshooting save
many hours of equipment downtime and
costly repairs?
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!
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
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, meters…smoke!
• Look for degraded performance as well; degraded
performance often leads to equipment failure
• Know your equipment!
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?
• 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!
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
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
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
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?
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!
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
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.
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
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
– Don’t 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.
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 burnout of system components
– Excessive current usage causing defective fuses
– Intermittent faults that cause random failure
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!
Symptom
Recognition
Symptom
Elaboration
Listing of
Probable
Faulty
Functions
Localizing
the Faulty
Function
Localizing
Trouble to
the Circuit
Failure
Analysis