Lesson 74 - Troubleshooting

Troubleshooting is the art of finding a problem, isolating it down to the source, so that you can replace the faulty component and restore proper operation of a circuit.

Whether you are designing a new piece of electronics equipment, or repairing that old tube radio you found at a garage sale, you will need to use some basic troubleshooting concepts.

The basics of troubleshooting is to create an organized plan to aid you in repairing faulty electronic equipment more rapidly and reliably. The time tested method I discuss here has been used for hundreds of years on all sorts of mechanical and electronic equipment, and been found to be the best method for determining and resovling a problem. No matter what piece of equipment you have, there are certain methods that work to aid you in finding a fault faster and more reliably. Those methods can be broken down into 7 steps

A) Determine Symptom(s)
B) Sectionalize
C) Localize
D) Isolate
E) Repair
F) Bench Test

A) Determining Symptom. Look at the equipment. What is it doing that it shouldn't be? What isn't it doing that it should be? In order to determine what needs fixed, you must first determine what is wrong. This means you need a basic understanding of what the equipment is supposed to do and how it works under normal conditions. Lets assume for a this discussion that we are repairing a radio receiver. You turn it on, and the lights come on, but there is no sound coming out of the speaker. You turn the tuning knob, switch radio bands, nothing. The symptom in this case is: Power but not audio. Write that down.

The symptom lets you know what is wrong with the equipment, so you can determine what you need to check. You have to analyze the symptom as to how it affects the proper operation of the equipment. The symptom will always provide clues that show you where to look (and where not to look) for the trouble, saving precious time.

B) Sectionalize. Once you recognize the symptom,the next step is to break the equipment down into sections in your mind. In the case of our radio, we have a Power Supply section, a tuner section, a mixer section, a local oscillator section, and an audio section. Sectionalizing means determining which section the problem is in. This requires some knowledge of how the equipment works, at least at a block diagram level. In this case, the lights come on, indicating that the power supply is at least partially functional. You may want to break out a multimeter at this time and make sure the power supply is putting out all the proper voltages, as a faulty power supply can cause any number of problems, but if the meter shows that it has the right voltages coming out, then you have at least eliminated that section.

This is how troubleshooting works. You use a divide and conquor method to solve the problem. Split the equipment up in your mind. Is the problem in the power supply, or somewhere after it? Power is good, we move on. Now we break out some other piece of test equipment. An oscilloscope works wonders to find out if the RF, IF, and Local Oscillators are working properly. Usually, if you get a signal at all out of them, they are good. Granted - if the symptom was "receiving off frequency" you might want to check out these areas in more detail, making sure the L.O. is on proper frequency, etc, but in this case, they are all working, and we move on to the Audio section. We have successfully Sectionalized the problem.

C. Localize. After you have located the faulty section (in this case the Audio section), the next step is to localize the problem to a particular circuit or stage. Check the input with our scope. Do we have audio going into the first amplifier? Do we have audio coming out of the last amplifier? Is the audio coming out larger than the audio going in? If the answer is no, then we examine the circuit closer. Each transistor is an amplifying stage - with multiple components in the circuit required to make the transistor work. It has noise suppression filter capacitors and biasing resistors. If one resistor is bad, the whole amplifier doesn't work. So by localizing the problem to a given transistor, we can then move on to isolating it to the exact component (resistor for instance) that is causing the transistor not to be biased, and therefore not to amplify. Oddly we find that our final amplifier has all kinds of sound coming out of it. The outgoing signal on the oscilloscope is much larger in amplitude than the incoming signal. So why do we hear no sound?

D. Isolate. We have localized the problem. We know that there is audio coming out of the final amplifier, but still no sound at the speaker. It is time to isolate the problem to the exact component that is causing the headaches.

Often, this can be done by a simple visual inspection. Is the capacitor bloated with the heat shrink melted down? Is there a burned up resistor. Use all your senses. A burned up transformer has a very distinct smell. Sometimes you can detect a bad IC by feeling it. Turn off the lights and check for arcing. Many times I have found problems in extremely high tech equipment using only the test equipment I was provided at birth - Eyes, Ears, Nose, etc. In this case, I'll need something more.

I use my scope and find that there is no audio at the speaker. I do have audio at the amplifier. The problem must be somewhere inbetween. I follow the wires and find that there is a headphone jack between the two. The jack is old, and there is some debris/corrosion on it. That corrosion is causing the connectors to not make proper contact, and the jack thinks I have my headphones plugged in, which of course turns off the speaker.

E Repair: I can either clean the jack, or replace it. Each has its good points and bad points. Replacing costs more, but is more reliable in the long run.

F Check for proper operation. After soldering in the jack, I put headphones in, and they work fine. I remove them, and the speaker works. I check the volume control in several positions, and change frequencies. I go completely through the equipment to see if there may be other problems in it that were not reported.    
Previous
Next Post »
My photo

Hi, I`m Sostenes, Electrical Technician and PLC`S Programmer.
Everyday I`m exploring the world of Electrical to find better solution for Automation. I believe everyday can become a Electrician with the right learning materials.
My goal with BLOG is to help you learn Electrical.
Related Posts Plugin for WordPress, Blogger...

Label

KITAIFA NEWS KIMATAIFA MICHEZO BURUDANI SIASA TECHNICAL ARTICLES f HAPA KAZI TU. LEKULE TV EDITORIALS ARTICLES DC DIGITAL ROBOTICS SEMICONDUCTORS MAKALA GENERATOR GALLERY AC EXPERIMENTS MANUFACTURING-ENGINEERING MAGAZETI REFERENCE IOT FUNDAMENTAL OF ELECTRICITY ELECTRONICS ELECTRICAL ENGINEER MEASUREMENT VIDEO ZANZIBAR YETU TRANSDUCER & SENSOR MITINDO ARDUINO RENEWABLE ENERGY AUTOMOBILE SYNCHRONOUS GENERATOR ELECTRICAL DISTRIBUTION CABLES DIGITAL ELECTRONICS AUTOMOTIVE PROTECTION SOLAR TEARDOWN DIODE AND CIRCUITS BASIC ELECTRICAL ELECTRONICS MOTOR SWITCHES CIRCUIT BREAKERS MICROCONTROLLER CIRCUITS THEORY PANEL BUILDING ELECTRONICS DEVICES MIRACLES SWITCHGEAR ANALOG MOBILE DEVICES CAMERA TECHNOLOGY GENERATION WEARABLES BATTERIES COMMUNICATION FREE CIRCUITS INDUSTRIAL AUTOMATION SPECIAL MACHINES ELECTRICAL SAFETY ENERGY EFFIDIENCY-BUILDING DRONE NUCLEAR ENERGY CONTROL SYSTEM FILTER`S SMATRPHONE BIOGAS POWER TANZIA BELT CONVEYOR MATERIAL HANDLING RELAY ELECTRICAL INSTRUMENTS PLC`S TRANSFORMER AC CIRCUITS CIRCUIT SCHEMATIC SYMBOLS DDISCRETE SEMICONDUCTOR CIRCUITS WIND POWER C.B DEVICES DC CIRCUITS DIODES AND RECTIFIERS FUSE SPECIAL TRANSFORMER THERMAL POWER PLANT cartoon CELL CHEMISTRY EARTHING SYSTEM ELECTRIC LAMP ENERGY SOURCE FUNDAMENTAL OF ELECTRICITY 2 BIPOLAR JUNCTION TRANSISTOR 555 TIMER CIRCUITS AUTOCAD C PROGRAMMING HYDRO POWER LOGIC GATES OPERATIONAL AMPLIFIER`S SOLID-STATE DEVICE THEORRY DEFECE & MILITARY FLUORESCENT LAMP HOME AUTOMATION INDUSTRIAL ROBOTICS ANDROID COMPUTER ELECTRICAL DRIVES GROUNDING SYSTEM BLUETOOTH CALCULUS REFERENCE DC METERING CIRCUITS DC NETWORK ANALYSIS ELECTRICAL SAFETY TIPS ELECTRICIAN SCHOOL ELECTRON TUBES FUNDAMENTAL OF ELECTRICITY 1 INDUCTION MACHINES INSULATIONS ALGEBRA REFERENCE HMI[Human Interface Machines] INDUCTION MOTOR KARNAUGH MAPPING USEUL EQUIATIONS AND CONVERSION FACTOR ANALOG INTEGRATED CIRCUITS BASIC CONCEPTS AND TEST EQUIPMENTS DIGITAL COMMUNICATION DIGITAL-ANALOG CONVERSION ELECTRICAL SOFTWARE GAS TURBINE ILLUMINATION OHM`S LAW POWER ELECTRONICS THYRISTOR USB AUDIO BOOLEAN ALGEBRA DIGITAL INTEGRATED CIRCUITS FUNDAMENTAL OF ELECTRICITY 3 PHYSICS OF CONDUCTORS AND INSULATORS SPECIAL MOTOR STEAM POWER PLANTS TESTING TRANSMISION LINE C-BISCUIT CAPACITORS COMBINATION LOGIC FUNCTION COMPLEX NUMBERS ELECTRICAL LAWS HMI[HUMANI INTERFACE MACHINES INVERTER LADDER DIAGRAM MULTIVIBRATORS RC AND L/R TIME CONSTANTS SCADA SERIES AND PARALLEL CIRCUITS USING THE SPICE CIRCUIT SIMULATION PROGRAM AMPLIFIERS AND ACTIVE DEVICES BASIC CONCEPTS OF ELECTRICITY CONDUCTOR AND INSULATORS TABLES CONDUITS FITTING AND SUPPORTS CONTROL MOTION ELECTRICAL INSTRUMENTATION SIGNALS ELECTRICAL TOOLS INDUCTORS LiDAR MAGNETISM AND ELECTROMAGNETISM PLYPHASE AC CIRCUITS RECLOSER SAFE LIVING WITH GAS AND LPG SAFETY CLOTHING STEPPER MOTOR SYNCHRONOUS MOTOR AC METRING CIRCUITS APPS & SOFTWARE BASIC AC THEORY BECOME AN ELECTRICIAN BINARY ARITHMETIC BUSHING DIGITAL STORAGE MEMROY ELECTRICIAN JOBS HEAT ENGINES HOME THEATER INPECTIONS LIGHT SABER MOSFET NUMERATION SYSTEM POWER FACTORS REACTANCE AND IMPEDANCE INDUCTIVE RESONANCE SCIENTIFIC NOTATION AND METRIC PREFIXES SULFURIC ACID TROUBLESHOOTING TROUBLESHOOTING-THEORY & PRACTICE 12C BUS APPLE BATTERIES AND POWER SYSTEMS ELECTROMECHANICAL RELAYS ENERGY EFFICIENCY-LIGHT INDUSTRIAL SAFETY EQUIPMENTS MEGGER MXED-FREQUENCY AC SIGNALS PRINCIPLE OF DIGITAL COMPUTING QUESTIONS REACTANCE AND IMPEDANCE-CAPATIVE RECTIFIER AND CONVERTERS SEQUENTIAL CIRCUITS SERRIES-PARALLEL COMBINATION CIRCUITS SHIFT REGISTERS BUILDING SERVICES COMPRESSOR CRANES DC MOTOR DRIVES DIVIDER CIRCUIT AND KIRCHHOFF`S LAW ELECTRICAL DISTRIBUTION EQUIPMENTS 1 ELECTRICAL DISTRIBUTION EQUIPMENTS B ELECTRICAL TOOL KIT ELECTRICIAN JOB DESCRIPTION LAPTOP THERMOCOUPLE TRIGONOMENTRY REFERENCE UART WIRELESS BIOMASS CONTACTOR ELECTRIC ILLUMINATION ELECTRICAL SAFETY TRAINING FILTER DESIGN HARDWARE INDUSTRIAL DRIVES JUNCTION FIELD-EFFECT TRANSISTORS NASA NUCLEAR POWER SCIENCE VALVE WWE oscilloscope 3D TECHNOLOGIES COLOR CODES ELECTRIC TRACTION FEATURED FLEXIBLE ELECTRONICS FLUKE GEARMOTORS INTRODUCTION LASSER MATERIAL PID PUMP SEAL ELECTRICIAN CAREER ELECTRICITY SUPPLY AND DISTRIBUTION MUSIC NEUTRAL PERIODIC TABLES OF THE ELEMENTS POLYPHASE AC CIRCUITS PROJECTS REATORS SATELLITE STAR DELTA VIBRATION WATERPROOF