Evidence-Based Diagnostic Method
Canonical Definition
An evidence-based diagnostic method defines the symptom and operating state, identifies the affected signal or power path, ranks plausible causes, performs safe discriminating tests, records the result, and verifies the final repair without introducing untracked changes.
Symptom Is Not Cause
| Observation | Possible causes | Useful next distinction |
|---|---|---|
| RPM-related whine | shield current, charging ripple, switching pickup, source reference | signal-side versus power-side isolation |
| Amplifier protects on bass | supply loss, low load, short, heat, internal fault | load disconnected plus terminal-voltage capture |
| One channel silent | source, routing, cable, amplifier, wiring, driver | single-boundary channel swap |
| Turn-on pop | source step, DSP unlock, mute order, remote timing, amplifier transient | common-time-base capture |
The Diagnostic Loop
- Make it observable: describe what changes, where, and when.
- Reproduce it: confirm the original condition safely.
- Freeze the baseline: record controls, routing, voltage, load, temperature, and source state.
- Form a hypothesis: name one mechanism that could explain the evidence.
- Predict both outcomes: write what pass and fail mean before testing.
- Change one variable: run the smallest safe discriminating test.
- Narrow the boundary: keep the last known-good and first known-bad points.
- Repair the confirmed cause: do not replace unrelated parts.
- Verify: repeat the original failure condition and nearby conditions.
Required State Record
- vehicle, key, engine, charger, stop-start, and sleep state
- source, file, connection, preset, volume, and controls
- channels, crossovers, loads, gains, remotes, and protection indicators
- battery and device-terminal voltage
- ambient and component temperature
- motion, vibration, road condition, and time to failure
Stop-Now Conditions
Stop testing for smoke, burning odor, melted insulation, arcing, repeated fuse operation, sustained DC, unstable high-current terminals, or unexpected full-level output.
Preserve the evidence, de-energize safely, and inspect before continuing.