principle of troubleshooting. topic problem solving analysis circuit faults testing basic components...

Principle of Troubleshooting

Topic Problem solving analysis Circuit faults Testing basic components

Troubleshooting methods Voltage measurement

Amperage measurement Resistance measurement Substitution Bridging Heat Freezing Signal tracing & injection Component testers & test lamps Resoldering Adjusting Bypassing

Problem solving analysis

Servicing a device has 3 phases:1) Situational analysis2) Problem solving3) Decision making

1) Situational analysis Asking questions and observations as follows:

Discuss the defect with the owner or operator Compare the problem with others from past

experiences Perhaps there is no problem at all, and it is an

operating error Identify the existing state of operation with the desired

state Make an overall observation of the situation, noting

symptoms and relevant changes.

2) Problem solving Get organized:

Describe the problem

Compare the problem situation with known operating conditions prior to the breakdown

Describe all known differences such as the symptoms, noises, and smells noticed when defect occurred

Compare the ‘what is’ with the ‘what is not’. Which components are okay and which are not, and to what degree are the components defective?

Analyze differences through testing by paying close attention to obscure and indirect relationships. For example, slight tolerance changes in components or physical color changes can signal causation.

3) Decision making Examining various solutions or repair

alternatives and selecting the best option

Consider all the advantages and disadvantages for each alternative along with contingency planning

Contingency planning: future changes in the overall system such as expected life, operating conditions and model changes.

Circuit Faults Basic causes of electrical or electronic breakdowns:

1. Heat Increases the resistance of circuits

Increases the current Causes the materials to expand, dry out, crack, blister, and wear

down much more quickly

2. Moisture Causes circuits to draw more current Causes expansion, warping, quicker wear, and abnormal current

flow (short circuits).

3. Dirt and contaminants (fumes, vapors, abrasives, soot, grease, and oils) Causes devices to ‘clog’ or ‘gum’ up and operate abnormally until

they finally break down

4. Abnormal or excessive movement Vibrations and physical abuse can lead to breakdowns

5. Poor installation Unqualified installer, careless and rushing installation

Failure to tighten a bolt Failure to properly solder a wire connection

6. Manufacturing defect

7. Animals and rodents

Circuit Faults (cont..)

4 most common causes of circuit faults:1. Short circuit

Draw more current because resistance decreases and results in voltage decreases.

Typical signs of short circuits are blown fuse, increased heat, low voltage, high amperage, smoke

2. Open circuit Infinite resistance and zero current Typical signs are infinite resistance, zero amperage, and

completely inoperable device


3. Ground Wires with poor insulation, pinched wires or misplaced

components. Typical signs are abnormal amperage, voltage and

resistance reading, shocks, abnormal circuit performance, tripped ground-fault interrupters, and periodic blown fuses or circuit breakers

4. Mechanical fault Too much friction, wear, abuse, or vibration

Broken belts, worn bearings, loose bolts, damaged chasis etc Typical signs are noisy operation, abnormal operation, visual

clues, and circuit failure


Troubleshooting methods1. Voltage measurements

Use voltmeter or oscilloscope, in parallel with the circuit A zero voltage may identify an open circuit, a low voltage may

indicate a short circuit.

Amperage measurements Use ammeter or a ‘clamp-on’ ammeter in series with the

circuit. Indicates and locates common circuit faults such as short

circuit, open circuit and grounds.

Resistance measurements Use ohmmeter. Always shut off the power before measure

resistance. Locates short circuit, open circuit and grounds.

4. Substitution Replacing a suspected faulty component with a

known good component.

5. Bridging ‘jumps’ or placing a known good component across

the suspected faulty component in a circuit. Limited to open-circuited components. Bridging a

short-circuited components may have no effect or may cause damage to the new component

Troubleshooting methods

6. Heat Usually by using a hot blower Applied to a suspected ‘intermittent’ component. Thermally

intermittent component breaks down under heat.

7. Freezing Use of cold air from a fan or a chemical coolant. Cools the suspected thermally intermittent component, thus

temporarily restore the component to normal operation.

8. Signal tracing & injection Most often used in servicing radio receivers. A signal is injected into various points of a process (stage) in

order to locate the specific inoperable stage.


9. Component testers, test lamps Instruments used to test the quality of a component Megohmmeters, capacitor checkers, test lamps, transistor or

diode testers, cathode-ray-tube (CRT) checkers, IC testers etc.

10. Re-soldering, adjusting and aligning. Poor electric solder connection (cold solder joint)

11. Bypassing To locate a suspected problem. Requires unplugging one of several circuits


Testing basic components Most common defects of resistors are physical –

cracking and charring. Excessive current and heat tend to increase the resistance.

Ohmmeter – measure continuity or resistance in resistors or other components. Component having continuity has a resistance near

zero Component having no continuity has infinite

resistance.

Continuity measurement: (fuse, wires, cables or cords) A good fuse, wire, cable or cord will have continuity (0

ohm) A blown fuse or broken wire, cable or cord will have

no continuity (infinite resistance). Gently bend the wire at various points especially

along common faults such as near connections.

Testing basic components

Continuity measurement: (switch)A single pole, single throw switch should have

continuity when closed and no continuity when opened.

Gently rock the switching mechanism to identify potential intermittent circuit faults.


Potentiometer 1 lead of the ohmmeter placed on the center terminal,

and the other lead on one of the end terminals. The potentiometer should vary the resistance

accordingly when turned. Another way to test a potentiometer is to turn the

potentiometer while it is in the circuit. If a scratchy, rough sound is heard in the speaker, the potentiometer needs cleaning or replacing.


BatteriesVoltage or amperage testingAn excellent battery should exceed its rated

value. For example, a new dry cell rated at 1.5 V should measure 1.5 V to 1.6 V. Old and weak battery will read less than 1.5 V


SpeakersRattles and heavy vibration are often signs of

a defective speaker.Visually inspect for cracks, dirt, and other

faults.Substitution is the best testing technique.

Replace with a speaker that have the same impedance and power ratings.


Speakers (cont..)Defective due to a bad voice coil, connection:

gently pressing on the speaker cone may operate the speaker.

Place an ohmmeter across the voice coil terminal

Listen and watch for a small ‘pop’ sound and movement of the speaker cone. A defective speaker will show no movement or popping sound.


Speakers (cont..)Phasing 2 or more speakers:

Place the ohmmeter on the voice coil terminal and note whether the cone moves in or out. Reversing the polarity will reverse the movement. Mark the positive side of each cone when it is in the out position. Then connect each speaker to the audio amplifier while observing the correct polarity.


Capacitors Techniques to test capacitors:

Resistance measurement (ohmmeter)1) Make sure the capacitor has discharged2) Place the ohmmeter on a high scale such as 10,000 ohm3) Place the leads of the ohmmeter across the leads of capacitor4) The needle should deflect upward and then slowly drop back

down to near zero Failure to deflect : open capacitor Failure to drop down: short circuited capacitor

Capacitance measurement (capacitor checker) To check capacitance, leakage and opens.



Spark test1. Momentarily (1 sec) connect the capacitor across the

voltage source. Make sure the voltage does not exceed the voltage rating specified on the capacitor.

2. Short its terminals together using a screwdriver or a similar device with an isolating handle.

3. A good capacitor will show a spark



Bridging Suspected defective capacitor is bridged (jumped) with

a known good capacitor within +10% of the rated value. Substitution

Replaced with a capacitor of the same rating/specifications


Inductor

It can be tested using meter ohm analog, meter ohm digital and RCL meter

Condition Meter Ohm Meter RCL Good 10Ω, 50Ω, 100Ω Reading

Broken ∞ (open loop) No reading

Fuse

Use ohm meter for testing Good fuse: reading must be between 0 –

10 ohm Broken fuse: reading infiniti

Diode Use meter ohm

Forward bias Reverse bias-Probe +ve is connected to anode -probe –ve is connected to cathode Good diode: reading is low resistance

-Probe +ve is connected to cathode -probe –ve is connected to anodeGood diode: reading is infinity

Transistor

transistor is two back-to-back diodes in one package as shown.

The letters C, B, E stand for COLLECTOR, BASE, EMITTER which are the names of the three leads which come out of a transistor.

Transistor (cont)

Assuming you know if the transistor is NPN or PNP, and assuming you know where B, C, and E are, then just test the B-C junction and the B-E junction as if they were standard diodes. if one of those junctions is a "bad diode", then the transistor is bad.

Also, check the resistance from C to E using a higher Ohms scale.

If the transistor is good, you should get an open-circuit reading from collector to emitter.

Transistors (cont)

USING METER TO SEPARATE NPN FROM PNP If you have a transistor but you don't know if it is NPN or PNP, then you can find out which it

is using Ohm-meter. Assuming C, B, and E are known on the transistor, do the following: - Connect the positive

lead of your Ohm-meter to the base. - Touch the other lead of your meter to the collector. If you get a reading, the transistor is NPN.- To verify, move the lead from the collector to the emitter and you should still get a reading.

If your meter reads open-circuit, then connect the negative lead to the base and touch the positive lead to the collector. If you get a reading, then the transistor is PNP. Verify by measuring from base to emitter.

THANK YOU

principle of troubleshooting. topic problem solving analysis circuit faults testing basic components...

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