First read AG post.
First visual inspection burned part, bulging caps, broken leads/wires...
Any bad smell like a leaking cap or burned part
Reseat all plug connectors to renew the contact area, vibration and contacts are not a good mix.
One of the first things I look at with a system with a speaker and a PCB amp(s)(guitar/bass amps powered speakers etc) are the solder connections at the PCB at the devices that have the most mass(power supply caps inductors etc). Mass and vibration can stress and cause the connection to fail or be intermittent. Also look at the PBC traces for breaks look around the middle on the most unsupported area that area often flexes the most.
After that look at the circuit and check if it is from a companies parts app. Say it is a IC based one look up the IC and find the app note. The circuit might be right from the app note or very close.
Then you can start testing devices with meters and checking the circuit with a DMM and a scope etc.
Standard troubleshooting stuff
