Module 20: Troubleshooting Methodology
Sooner or later, everything stops working — a power supply, an amplifier, a project you built yourself, or a piece of equipment someone hands you. Troubleshooting is the skill of finding out why, quickly and without making things worse. It is not guesswork or luck: it is a method. This final module teaches that method and the techniques that support it, then puts them all to work on complete repairs of commercial equipment and on bringing up new home-built projects.
- Apply a systematic, most-likely-cause-first method to any fault
- Use half-split testing to find a fault in a long chain of stages
- Find dead and degraded stages with signal injection and signal tracing
- Use substitution correctly, as a test rather than a guess
- Predict and measure in-circuit voltages and currents safely
- Use an oscilloscope to find clipping, oscillation and power-related faults
- Diagnose common faults in power supplies, amplifiers and microcontroller projects
Module Overview
The first lesson sets out the systematic method that everything else in the module supports: observe, gather information, form a hypothesis, test, narrow, confirm, repair and document. The next five lessons are the techniques used inside that method — divide and conquer, signal injection, signal tracing, substitution, and in-circuit voltage and current measurement.
The scope lesson extends signal tracing to power amplifiers, RF and fast signals, where waveform shape tells you more than any meter reading. The common faults catalog then gives you a ranked starting list for the symptoms you will meet most often.
The module ends with two lessons of complete worked examples: four repairs of everyday equipment, and four home-built workbench accessories brought up from their first power-on, showing how the techniques combine into fast, confident diagnoses.
Lessons
Systematic Fault Finding
Systematic Fault Finding
The eight-step method, most-likely-cause-first, troubleshooting tools, safety, keeping a log, and a worked example.
Divide and Conquer
Divide and Conquer
Half-split testing in about log2(N) steps, choosing split points, power supply chains, and its limitations.
Signal Injection
Signal Injection
Injecting a test signal and working backward from the output, injector tools, signal choice, and a worked example.
Signal Tracing
Signal Tracing
Following a real signal forward, knowing what correct looks like, reading clues, and an amplifier example.
Substitution Method
Substitution Method
Component, cable, module and unit substitution, rules for valid swaps, the device-or-connections test, and dangers.
Voltage and Current Measurements In-Circuit
Voltage and Current Measurements In-Circuit
Predict then measure, voltage fault patterns, current without breaking the circuit, and live-circuit safety.
Using a Scope to Trace Signals
Using a Scope to Trace Signals
Protecting the scope, bandwidth and probe loading, the two-tone envelope test, and spotting parasitic oscillation.
Common Faults and Symptoms
Common Faults and Symptoms
A ranked catalog of faults in power supplies, amplifiers, microcontroller projects and equipment, with quick tests.
Repair Worked Examples
Repair Worked Examples
Four complete repairs: an amplifier, a bench supply, a powered speaker and a microcontroller project.
Building Workbench Accessories: Worked Examples
Building Workbench Accessories: Worked Examples
Four new builds brought up: a load bank, a current-limit box, an LED tester and a continuity tester.