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 burn-out 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