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

Why

Intermittent faults can arise for various reasons:

• Solder joints degrade over time and may become electrically or thermally intermittent
• Capacitors and resistors change both as they age and as they warm up during operation, altering their performance
• Transistors and diodes may develop internal leakage, causing gain changes and noise. This may appear as popping, rushing, crackling and whistling sounds, or even silence, which can be hard to trace. These faults may cause DC offsets, tripping equipment protection circuits.
• Electronic parts don’t generally show obvious signs of deterioration as they age. They must be tested, often under dynamic conditions, to establish functionality and health. There may be hundreds of electronic parts in a piece of equipment…

Which

Transistors are most likely to cause tedious intermittent faults and some types are more prone to doing so, a list of which I keep both electronically and in my brain! 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 approach 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 the cause of the problem and eliminate it.

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