What

Intermittent faults are the most annoying type of faults one comes across when working on electronics. They are commonly found in the domain of electronics and can be a royal pain in the ar$e

Intermittent faults are best described as faults that:

• Come, go and are not always present
• Can be difficult to trigger or replicate
• Are modulated by triggers like temperature, voltage and humidity

Why

Intermittent faults can arise for various reasons:

• Solder joints degrade over time and may become electrically resistive and thermally intermittent
• Capacitors and resistors change as they age and as they warm up during operation, altering their performance
• Customer equipment set-up and use patterns may cause intermittent faults that are related to another piece of equipment, a cable, etc.
• Transistors and diodes may develop internal leakage, causing gain changes and noise. This may present as popping, rushing, crackling and whistling sounds, or even silence, which can be hard to trace. Semiconductor faults often cause variable DC offsets, tripping equipment protection circuits.
• Electronic parts don’t generally show obvious signs of deterioration as they age. They must be tested, usually under dynamic conditions, to establish functionality and health.

Which

Transistors are most likely to cause tedious intermittent faults, and some types are more prone to doing so. You don’t want to replace every transistor in the hope of resolving something like this. That’s a costly, wasteful process that may change the sonic character of the equipment and cause other issues when carelessly done, as it often is.

With the component-level repair necessary when working on older hi-fi equipment, one should always find the culprit/s and replace them, and others like them, where necessary. In other words, we always want to find and eliminate the cause of the problem. This is not the domain of recappers…

Paradoxically, even reworking dry joints associated with a bad transistor can sometimes ‘cure’ it for days or weeks, only for the problem to reappear, making finding them even harder. Fixing these problems is where we earn our money and lose our hair.

Fixes

Resolving these faults can be technically challenging, especially if the fault disappears as they do. There are ways and means of coaxing these faults out of hiding, but equipment will occasionally need a couple of visits for problematic intermittent faults to be exterminated.

Whilst intermittent faults are tedious, they are also extremely satisfying to resolve. Some of my best repairs have been when resolving intermittent faults, like with this Technics SE-A5 power amplifier.

Just remember this, though, before you go nuts at your technician for not fixing an intermittent fault: These are tricky faults to find, and their intermittent nature is no more my fault than it is yours, or your mum’s! Customers need to work with their repairer to deal with the worst of these faults, so patience may be required sometimes.