Intermittent faults in electronic equipment are some of the most challenging to resolve.

I’ve written this FAQ for all technicians, the good, the bad, and the ugly, because intermittent faults can be difficult to find and fix. This is because:

• They are not always present, appearing and disappearing, sometimes unpredictably
• They may be modulated by ‘triggers’ like temperature, voltage, signal level and humidity
• They can be difficult to trigger, and the harder to trigger, the harder to find and fix
• When not present or reliably triggerable, they are essentially untraceable

Causes

• Solder joints degrade over time and may become electrically resistive and intermittent
• Capacitors and resistors change as they age and as they warm up during operation
• Customer equipment set-up may cause or trigger intermittent faults
• Transistors and diodes may develop leakage, causing gain changes and noise such as popping, rushing, crackling and whistling, or silence
• Semiconductor faults often cause DC offsets, which may trip protection circuits.
• Mechanical signal path contacts can oxidise and degrade, most commonly in switches, potentiometers and relays

Transistors are most likely to cause intermittent faults, with some types especially prone. Electronic parts don’t generally show visual signs of deterioration, so they must be tested. This is best done under dynamic conditions, as static testing often fails to reveal intermittent transistor issues.

Good technicians always want to find, understand and eliminate a problem. This is essentially trend analysis, which builds knowledge and saves time later. Recapping rarely solves intermittent faults and never leads to an understanding of which part caused a problem.

Fixes

Resolving intermittent faults can be challenging, and equipment will occasionally require more than one visit to eliminate the most problematic intermittent faults. Whilst painful, these faults are also extremely satisfying to fix. Some of my best repairs involve resolving intermittent faults, like with this Technics SE-A5 power amplifier.

Just remember that the problematic nature of these faults is no more your technician’s fault than it is yours. I’ve occasionally had customers get upset with me for not finding/fixing a fault that never presented itself to me, and that’s as silly as getting upset with me about the weather!

These faults are what they are, a quirk of complex electronics, and whilst good technicians will be able to resolve most of these faults, customers need to work with their technicians when dealing with them.