Troubleshoot 'no signal' by tracing from source to output; troubleshoot 'unwanted signal' by tracing from output to source

Systematic signal tracing follows two opposing directions depending on the symptom. For absence of signal: verify the source, then trace forward (source → cable → first processing stage → next cable → …) until signal reappears — the stage after the last confirmed signal is the fault. For unwanted signals (hum, noise, buzz, distortion): start at the amplifier output and work backward (disconnect amplifier input — if noise remains, amp is the source; if noise disappears, source is upstream). At each stage, disconnect the input cable and either measure signal or substitute a known-good source. Make changes one at a time. Systematic elimination prevents chasing false leads and allows confident diagnosis. Intuition and experience complement but never replace the logical trace.

Examples

No sound from a monitor speaker: check that the monitor console is powered, channel is assigned and unmuted, amp is on, speaker cable is connected. Substitute the monitor console output cable with a known-good cable. Substitute the amp. Substitute the speaker. Fault found = amp.

Assessment

A system has persistent 60 Hz hum. You disconnect the power amplifier input and the hum disappears. What does this tell you about the source of the hum? What is your next step?