12 years in field service, you pick up a few tricks.

Intermittent overspeed fault on a servo motor. Cycle the power, fault clears, runs fine for a few days, then it's back. Drive replaced. Motor replaced. Wiring "checked". When someone says they checked the wiring, it's usually a visual check. Doesn't catch this. My trick: run a long wire to the pin at the motor plug, continuity test from the far end, measure resistance on each wire individually. Should be around 1 ohm. Pink wire came back at 70 ohms. That's not a wire fault, that's a connection fault. Pin wasn't properly seated in the plug. Faults like this get power-cycled away for years without ever getting fixed. The drive and motor were never the problem.

Electrical troubleshooting
Industrial maintenance
FST Life
Field Service Technician