Technician Procedures
Knowing the theory is half the job; the other half is a systematic method for finding and fixing faults. This is what separates a technician from a parts-swapper. The Associate CET exam tests whether you can troubleshoot logically rather than by guesswork — this guide covers the standard methods.
Effective troubleshooting is narrowing the possibilities efficiently. Every measurement you take should cut the number of suspects roughly in half, not just confirm what you already believe. The goal is to locate the fault with the fewest tests, then verify the fix actually solved the reported problem — and didn't create a new one.
- Identify the symptom. Get a clear, specific description of what's wrong. "It doesn't work" isn't a symptom; "no audio output but the power LED is on" is.
- Gather information. What changed? Recent repairs, a power surge, dropped unit? Check the obvious first — power, fuses, connections, settings.
- Form a hypothesis. Based on the symptom and how the circuit works, list the stages that could produce it. Use the block diagram.
- Localize the fault by dividing the system — test at the midpoint to cut the suspect area in half (the half-split method, below).
- Isolate to the component. Within the bad stage, measure to find the specific failed part.
- Repair using correct procedures and replacement parts.
- Verify & test. Confirm the original symptom is gone, the unit works fully, and no new fault was introduced.
When a signal passes through a chain of stages, half-splittingiHalf-split (binary search): test in the middle of the chain. If the signal is good there, the fault is downstream; if bad, it's upstream. Each test halves the remaining suspects — far faster than checking stage by stage. is the fastest way to find the dead stage. Instead of testing every stage from the input, you test in the middle first. The result tells you which half the fault is in, and you repeat — each measurement halves what's left.
Signal tracing
Start with a known-good signal at the input and follow it stage by stage with a scope or probe until it disappears — the fault is at that stage. "Following the signal forward."
Signal injection
Inject a test signal at successive stages, working back from the output, until you get output. "Working backward from the speaker/screen."
Both home in on the same answer from opposite ends. The half-split method tells you where to start tracing or injecting so you reach the fault faster.
| Symptom clue | Points toward |
|---|---|
| Completely dead | Power supply, fuse, power connection |
| Intermittent | Cracked solder joint, loose connector, thermal fault |
| Works then fails when warm | A component drifting with temperature |
| Distorted output | Bias error, failing stage, overdriven input |
| Hum in audio | Power-supply filter capacitor |
Trustworthy troubleshooting depends on trustworthy measurements: set the meter to the correct function and a range above the expected value, observe polarity on DC, account for meter loading on high-impedance nodes, and always compare against the expected value from the schematic or service data. A reading only means something relative to what it should be.