Cursitor Doom wrote:
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When inspecting a board for the likely cause of an intermittent fault
believed to be induced by warming up over time from switch-on,


** If the problem appears after a time delay an warming - it ain't a ****ing intermittent.

FYI:

I was presented with a Yamaha digital reverb some years ago ( model R1000) that worked fine until it got a bit hot. Then it broke into a very loud, harsh noise - bit like pink noise.

The only thing I could find that triggered the noise was heating the micro-controller with my soldering iron - so I ordered a new one ( not cheap) and fitted it. Made no ****ing difference.

So I rang the Australian agent and described the problem to one of their staff service people - with an Asian accent (his not mine) - he went off and checked the files for relevant service bulletins.

Came back with one entitled "Big Noise".

" If the unit emits a loud noise when operating in a high ambient temp replace ICs 1,2 3, 4 ,5 ,6 ... "

The problem was a damn design fault in the first 10,000 sold !!!

The fix was to replace all the regular CMOS data selectors with high speed ( HC ) ones. Once carried out, the problem vanished.

Seems the CMOS logic used had a timing issue, exacerbated by high temps.

More BS than this little Koala can bear ...


..... Phil